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The King's Cross fire: A correlation of eyewitness accounts and results of the scientific investigation
Fire Safety Journal 18 (1992) 105-121
The King's Cross Fire: A Correlation of Eyewitness Accounts and Results of the Scientific Investigation* A. F. Roberts~ Health and Safety Executive, Buxton, Derbyshire, SK17 9JN, UK
ABSTRACT During the 15-rain period, or thereabouts, between the first observation of the fire and its fatal eruption into the ticket hall, the fire at King's Cross Underground Station was observed by many witnesses. Naturally, their descriptions differed appreciably in points of detail, but, overall, they led to a reasonably consistent picture of the fire's development. This picture provided a vital frame of reference against which scientific description of possible sequences of fire development could be tested, particularly with respect to the last 1 or 2 rain prior to fire spread into the ticket hall. This paper presents the frame of reference provided by eyewitness accounts and the correlation with the outcome of the scientific investigation. 1 INTRODUCTION On Wednesday 18 November 1987, at approximately 19.30, the presence of a small fire on escalator No. 4 at the King's Cross Underground station was first reported. This fire developed relatively slowly for over 10min, but, shortly before 19.45, it began to develop much more quickly. At approximately 19.45, flames spread with cvasiderable rapidity into the ticket hall at the top of the escalator and * Paper presented at the I. Mech. E. seminar 'The King's Cross Underground Fire: Fire Dynamics and the Organisation of Safety', 1st June 1989. ~Present address: Nuclear Safety Research Management Unit, Health and Safety Executive, Broad Lane, Sheltield, S3 7HQ, UK.
105 (~) 1991 Crown Copyright.
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large quantities of thick, black smoke developed, spreading along all the passageways leading to street level exits. Scores of people had to flee for their lives through this smoke, and 31 people died as a result of the fire. The Public Investigation under Mr Desmond Fennell QC ~ heard evidence from many eyewitnesses of the different stages of the development of the fire. As with any body of eyewitness evidence, there were differences of emphasis and description and some anomalies, but there was also sufficient consensus for a reasonably reliable and detailed description of the fire's behaviour to emerge. The logs of the control centres of London Fire Brigade and British Transport Police and records of train movements on the London Underground system and at British Rail's St Pancras were used to provide time estimates for eyewitness evidence. Therefore, it was possible to construct not only a qualitative description but also a reasonably consistent chronology for the sequence of events. This detailed chronology provided an essential reference framework for the scientific investigation, in particular with respect to the rapidity of the fire's development at the time of entry of flames into the ticket hall. In comparing the eyewitness evidence with the findings of the scientific investigation, three areas of interest will be considered:
(1) (2) (3)
the initiation of the fire; the growth of the fire above the escalator, up to flashover; and smoke production and movement.
However, in order to put these comparisons into a context, some problems relating to eyewitness evidence will be considered and brief details of the station given. 2 PROBLEMS WITH EYEWITNESS EVIDENCE Apart from the normal problems with eyewitness evidence, deriving from the variability of human perception and recall of events, there were some additional complicating features at the King's Cross fire. The affected escalator was essentially a trench some 1.2m wide, 0.8 m deep and 40 m long, inclined at 30* to the horizontal. When viewing from either end, it was possible to make a reliable estimate of position in the nearer half of the escalator, but perspective effects make such estimates unreliable in the further half of the escalator; also eyewitnesses' perception of flames and smoke was substantially affected by viewing position. In particular, as it transpired, an eyewitness on
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escalator No. 6, looking across the escalator shaft, could only see the top of the trench of escalator No. 4. Low-lying flames within the escalator trench were obscured from view and attention was concentrated on flames emerging from the escalator trench. Eyewitnesses of the entry of flame into the ticket hail experienced a rapidly developing sequence of events. Initial descriptions differed appreciably as one witness concentrated on one 'frame' in the sequence and another on a different frame. Not surprisingly, not one witness was able to give a continuous and coherent account of the sequence of events, but the cumulative effect of their evidence gave a reasonably consistent picture.
3 STA'FION LAYOUT A full description of the station layout is given in the report of the Investigation ~ and a summary account is given in the papers by Moodie 2 and Crossland; 3 therefore, details are not reported here.
4 VENTILATION ARRANGEMENTS AT THE STATION The main source of ventilation at King's Cross station was air movements caused by the movement of trains. An Underground train fills an appreciable fraction of the cross-section of the running tunnels and causes a piston effect. The approach of a train drives air into the station and the departure sucks air out. This clearly gives rise to rapid fluctuations in air velocity throughout the station complex. The requirement is for four air changes per hour, with air velocities not exceeding 6.7 m/s on escalators aad stairways and 4.5 m/s in ticket halls. At King's Cross station there were two exhaust-fan ventilation shafts and two draught-relief shafts; details of these are given in Appendix I of the report of the Investigation. ~ A computation of the air velocities in the Piccadilly line escalator shaft and in the Victoria line escalator shaft for the period 19.30-19.50 on the night of the fire is shown in Fig. 1. This computation was based on the known layout of the station and the logged train movements in that period; it took no account of possible interfering effects of the developing fire. The cross-sectional areas of both escalator shafts are the same so that the algebraic sum of the two velocities gives a velocity proportional to
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3
A W
l :I
II .o_ 13
PICCADILLY LINE ESCALATOR SHAFT
2 1 0 -1 -2 -3
VICTORIA LINE ESCALATOR SHAFT
I:
÷ J~ E
NET AIR FLOW INTO TICKET HALL FROM ESCALATOR SHAFTS
>o ?-
-2 -3
19,30 19,32 19.34 19.36 19.35 19.40 19.42 19.44 19.46 19.48 19.50 Time
Fig. 1. Computed air velocities. NB The computation neglects the buoyancy effects of the fire, which would become dominant after 19.45. (See Fig. 17 of Ref. 1).
the net air flow from the two shafts into the ticket hall; this net velocity is also shown on Fig. 1. 5 THE INITIATION OF THE FIRE At about 19.30, several passengers travelling upwards on escalator No. 4 towards the ticket hall observed signs of fire beneath the escalator. Within the next 2-3 min the escalator was stopped, station staff were informed and a member of the British Transport Police (BTP), who happened to be in the ticket hall at the time, sent a radio message to the BTP control room requesting attendance by London Fire Brigade (logged at 19.33). The general experience of passengers travelling up escalator No. 4 while it was still moving, was that the signs of fire began about half way up on the right-hand side (looking up). Witnesses variously reported experiencing hot air or smoke above the escalator or seeing signs of flames or glowing beneath the escalator, via minor gaps between steps or between the moving steps and the stationary side of the escalator. Several witnesses spoke of seeing flames or sparks at more than one place beneath the escalator, possibly moving with the escalator.
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After escalator No. 4 was shut down, several other witnesses using escalator Nos 5 or 6 saw smoke or flames at more than one location. For example, at about 19.40, a witness walking up escalator No. 6 recalled seeing the reflections of flames half way up escalator No. 4 and again about three-quarters of the way up. The detailed examination of the scene of the fire, reported by Moodie, 2 showed that the lowest point of fire damage was on the right-hand running track of escalator No. 4 at a point adjacent to step 48 (counting from the bottom of the escalator, which had 101 steps visible). Ignition tests and the in-situ fire test showed the ease with which the layer of grease and detritus on the running track of the escalator could be ignited by a small flame, such as that on a burning match, to give an effect similar to that reported by eyewitnesses? The eyewitness evidence and the scientific evidence, therefore, agree on the initiation of the fire being beneath the escalator, at a point about half-way up on the right-hand side. There was no direct material evidence for the existence of more than one point of initiation, but there is strong eyewitness evidence for the establishment of a second seat of fire about three-quarters of the way up the escalator. Such multiple seats of fire are known from previous escalator fires and have been attributed to the spread of fire by burning material on the escalator chain, prior to the stopping of the escalator. This explanation is consistent with some eyewitness accounts. In the in-situ fire test the escalator was stationary, and in the actual fire conclusive material evidence of a second seat of initiation above step 48 would have been destroyed, so the lack of material evidence is not surprising.
6 THE GROWTH OF THE FIRE
6.1 19.30-19.43 At 19.32, a BTP policeman and a London Underground employee went down the stationary escalator No. 4 to inspect the fire. At that time, flames were just beginning to emerge from the gap between the stairs and the sides of the escalator over a length of about one step; this compares with the state of the in-situ fire test at about the 6-7 min stage, suggesting an ignition time of about 19.25. At 19.38, two further BTP policemen looked down escalator No. 4 from the ticket hall. They observed the fire as mainly on one side and stretching about half-way across the width of the escalator over one or
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two steps. The fire was clean burning, flames were about handrail height and the position of the fire was estimated at about half-way down.
In the period up to 19.43, other witnesses made somewhat similar observations, suggesting that the fire was established but developing rather slowly, in a manner consistent with the Health and Safety Executive (HSE) trials on a six-step section of escalator. Figure 1 shows that in the period 19.34-19.43, the air flow in this escalator shaft was either very low or was in a downwards direction. Therefore, it was not assisting the growth of the fire; if anything, it was restricting it. 6.2 19.43-19.46
In this period, it may be helpful to put estimated times to the nearest 15 s. These estimates are based on logged times of radio messages, estimates of travelling times from one point to another, etc. They are not highly accurate, but they do serve to give a feeling of the time-scale of a rapidly developing sequence of events. 19.42.45 Two fire appliances arrive and park in Pancras Road. Station Officer Townsley and Temporary Sub-Officer Bell enter station. 19.43.30 Townsley and Bell arrive at top of escalator No. 4 and confer. Townsley remains in charge in ticket hall, Bell descends escalator No. 6 to take charge below. 19.44.30 Bell arrives at bottom of escalator. 19.45.15 Mr Bates, a passenger, arrives in ticket hail. Mr Bates, PC Hanson and many others are suddenly exposed to smoke and flames. 19.46.00 PC Hanson is led to safety by PC Dixon at Euston Road (south) access point. There were, of course, many other observations complementary to these; they are broadly consistent with the above framework. On entering the ticket hall, Bell found it somewhat hot and smoky but not seriously so (19.43.30). On descending escalator No. 6, he looked across to escalator No. 4 and saw flames above the level of the handrail, bright and clear burning, comparable to those produced by the burning of a large cardboard box (19.44.15). On reaching the bottom of the escalator and looking up escalator No. 4, he saw flames on the hoarding on the left-hand side of the escalator shaft, having spread from the trench of escalator No. 4 (19.44.30).
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Three firemen looked down escalator No. 4 shortly after Bell left the ticket hall and reported seeing flames across the escalator, about 4 ft high and about one-third of the way down. They reported that there was not very much smoke from the fire (19.44.00). Three passengers, who were turned away from the foot of escalator No. 4 by Bell, reported seeing flames hallway up escalator No. 4, 5-6 ft high and 4-5 yards long, with flames shooting from both sides of the escaiator. (19.44.30). Bates entered the ticket hall from the Victoria line escalator at 19.45.15. He saw a relatively small flame at the top of escalator No. 4, between floor level and about 3 ft above the floor; he continued to make his escape across the ticket hall, but within a few seconds he experienced flames sweeping across the ticket hall towards him, accompanied shortly afterwards by thick, black smoke. PC Hanson, at about the same time, saw a jet of flame emerge from the top of escalator No. 4 and strike the ticket-hall ceiling. On the escalator side of the jet of flame, he could see unburnt ceiling; as the jet hit the ceiling, it turned into a layer of flame that rapidly spread outwards beneath the ceiling. Very shortly afterwards, massive quantities of clark smoke began to appear. Other eyewitnesses, mainly near the top of the Victoria line escalators, gave similar descriptions of a layer of flame spreading beneath the ceiling, hitting the side wall near the Victoria line escalator and being deflected downwards, filling in between the original layer and the floor, and the more or less simultaneous appearance of thick, black smoke. The 'best guess' is that a period of about 45 s elapsed between the fire beginning to develop strongly on the escalator (19.44.30) and flames entering the ticket hall (19.45.15). The eyewitness accounts show that even as the flames entered, there was relatively little smoke in the ticket hall---the massive flow of smoke came a few seconds after the entry of flame. The scientific investigation and the..',aking of statements began immediately after the fire, but much of the above details only began to emerge in cross examination. Essentially, a coherent eyewitness account was not available until March 1988, when the very short time interval of 45 s referred to ia the previous paragraph began to seem likely. Two schools of thought were apparent at that time--those who propounded flame spread predominantly on the escalator, and those who propounded rapid flame spread along the painted ceiling. The eyewitness evidence of Bates and Hanson strongly favoured the former,
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but no scientific witness at that time could produce a convincing explanation to meet the 45 s requirement. The Harwel! computations (presented in June 1988), experiments at Edinburgh University (July 1988) and the HSE model tests (carried out in July and August 1988) did provide the required convincing explanation. As the paper by Moodie and Jagger 5 shows, the 'trench effect' evident in the Harwell computations becomes established when flames involve both sides and the steps of the escalator trench; a fire that is involving a length of perhaps only two steps then begins to increase in length at a more or less exponential rate. As stated earlier, it seems likely that two independent seats of burning developed on escalator No. 4, the lower one near step 48 (about half-way up) and the other about three-quarters of the way up. In the ~3-scale model tests, once the trench effect had developed, the flame front spread from the half-way height to the ticket hall in 30-45 s. As fac as one can judge at this stage, the time-scale for flame spread in tl" models is not a function of linear scale, i.e. it can be related to a dimensionless distance scale. If this is so, then either position for the main seat of the fire, i.e. the one where the trench effect first developed, provides a satisfactory explanation of the 45-s interval before flames spread into the ticket hall. The trench effect provides a good explanation of the rate at which the flame spread in the upper part of the escalator. It also provides three additional points of agreement with eyewitness evidence.
(1)
(2)
The model tests showed a sequence of events as the flames entered the ticket hall that bears a close resemblance to the 'frames' from the sequence described by Bates, Hanson and others. The fire on the woodwork of the escalator burnt with very little smoke. Even when this fire was well developed, little smoke entered the model ticket hall, as appeared to be the case on the
night.
(3) The fire in the model kept very low and it was hard to assess its full dimensions from any one viewing point~ From the side, most of it was obscured by the sides of the escalator, and, from normal viewing positions at the ends of the trench, perspective effects limited the impression of size. Therefore, many puzzling aspects of the fire--its rate of spread, the relative lack of smoke before flashover, the lack of alarm in many of those witnessing it--stem from the trench effect. The interaction between the growth of the fire and the imposed
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ventilation is of interest. Figure 1 indicates that the air flow was downwards in the Piccadilly line escalator shaft from 19.40.30 to 19.43.30, thereby restricting the rate of growth of the fire. At 19.43.30, the flow switched to the upwards direction, reaching 2.9m/s by 19.44.30. This is the period during which the fire began its rapid accelertion up the escalator shaft. It may be that the change in air-flow condi~:ions from 19.43 onwards facilitated the development of the trench effect by removing an effect that was tending to keep the flames upright and substituting an effect that was tending to deflect the flames down into the escalator trench. Once the fire had begun to develop rapidly, its buoyancy effects would dominate the air flow pattern, and, from 19.45 onwards, the flow of air in the Piccadilly line escalator shaft was consistently upwards. On approaching the throat of the escalator shaft, as it enters the ticket hall, flames from the escalator trench spilled out to involve the whole cross-section of the shaft. This immediately exposed additional materials to fire attack--rubber, plastic, paint. The early stages of this attack may have been observed by some witnesses at the edge of the ticket hall who observed an increase in smoke flow, with changing sequence of colours, prior to the main smoke flow. It seems likely that the main smoke flow derived from the painted ceiling in the escalator shaft and in the ticket hail, as large surface areas of paint were suddenly exposed to a large heat source. The study of the painted ceiling in the escalator shaft was restricted by the complexity of the paint system. Accurate simulation of it was impossible. Only relatively small amounts of the actual paint system could be removed, adhered to its substrate, for examination. The indications from this examination were that, although fire was capable of spreading across the surface much more rapidly than if the paint had adhered to the substrate properly, the development of the ceiling fire was not rapid enough to make any major contribution to the sudden growth of the fire. It would appear that the trench effect is sufficient to account for the speed of development. On the other hand, it did appear likely that this paint system and other painted areas could have accounted for the sudden production of smoke. The deterioration in fire performance was shown to derive from the application of a modern, high-build paint system (six coats) to old paint, giving about 20 layers in total. Solvent from the most recently applied system was trapped to some extent in the old layers; the application of heat from the fire created solvent vapours, which blew large blisters in the upper paint layers.
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This delamination of the upper layers made the paint much more vulnerable to burning and created the increase in rate of flame spread that was observed in the tests. 6.3 19.46 onwards From 19.46 onwards, the fire was fully established in the Piccadilly line escalator shaft, where approximately 3.2 tonnes of material (mainly wood) burned in the main seat of the fire. Approximately 0.75 tonnes of material (mainly wood) burned in the ticket hail. In this phase, the fire burned as one would expect, with a large quantity of wood in an inclined shaft. The search-and-rescue operation and the fire-control operation of the London Fire Brigade dominated this period, and these are comprehensively described in Chapter 11 of the report of the Investigation. 1
7 SMOKE PRODUCTION AND MOVEMENT 7.1 An equivalent ventilation circuit for the station In order to gain an understanding of the movement of smoke during the fire, it is necessary to consider a representative ventilation circuit for the station; a full description would be very complex, but the main features of such a circuit are represented in Fig. 2. This schematic representation shows the six main levels of the station, using street level as a reference plane. Distance below street level (m) • approx. 6
Regl smoke 19 r
L
STREET LEVEL TUBE TICKET HALL LEVEL METROPOLITAN/CIRCLELINE LEVEL
0 4 7
SEAT OF FIRE
13
VICTORIA LINE LEVEL
16
PICCADILLY LINE LEVEL
21
NORTHERN LINE LEVEL
27
Fig. 2. An equivalent ventilation circuit (exhaust-fan shafts, draft-relief shafts and cross-passages omitted). Nodes 1-21 represent the junctions of airways; nodes 22-24 the actual and hypothetical seats of fire; 13-14, 15-16 and 17-18 the escalator shafts; and 6-19-20-21 the passageway to King's Cross Thameslink station.
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The five access points to street level from the ticket halls are denoted by nodes 1-5 (representing Euston Road (south), Euston Road (north), Pancras Road, St Pancras BR station and King's Cross BR station, respectively). A sixth access point to street level (node 6) was in the King's Cross Thameslink station. NodesT-10 represent the passageways leaving the tube ticket hall for the street-level access points. The passageway from 7 served access points 1 and 2, and a side passage (11) led to the Metropolitan/Circle line ticket hall at 12. The escalator shaft between the Victoria line and the ticket hall is represented by 13-14; the escalator shaft between the Piccadilly line and the ticket hall is represented by 15-16; and the escalator shaft between the Northern line and the Piccadilly line is represented by 17-18. The independent passageway from the tube platforms to King's Cross Thameslink Station is represented by 6-19-20-21. Other passageways, exhaust-fan shafts and draught-relief shafts are omitted for the sake of simplicity. The fire started at node 22 in escalator shaft 15-16, at approximately 12 m below street level. As stated in section 4, the driving force for the ventilation in normal circumstances was mainly provided by the movement of trains along the various lines, providing fluctuating air velocities throughout the station with some net air exchange between the station and the external atmosphere. When the fire started it remained relatively small until 19.43. However, as it rapidly grew from 19.43 onwards, it began to develop significant buoyancy forces in the escalator shaft 15-16. With the site of the fire 12 m below street level, the developed fire would have had a dominating effect on air movements, with a strong updraught in 15-16, lateral spread in the ticket hall (7-8-9-10), some downwards recirculation of air from the ticket hall into 13-14, and strong outflows in the passages between the ticket hall arid street level.
7.2 Smoke production and movement, 19.30-19.43 There was relatively little smoke production in this period. Some eyewitnesses reported discomfort or panic from the presence of smoke, but most reported no more than traces of smoke. As early as 19.35, a London Underground technician experienced smoke at the foot of the Victoria escalator (14); the route for this smoke movement is likely to have been up 15-16 and down 13-14, via
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the ticket hall. Figure 1 shows that, between 19.32 and 19.34, the air flow was up the Piccadifiy escalator shaft and down the Victoria escalator shaft, which is consistent with this view. At 19.37, two BTP policemen entered the station at the Euston Road (north) entrance (node 2 on Fig. 2) and observed white smoke issuing at this point. Figure 1 shows that, between 19.32 and 19.37, the air flow was either upwards or virtually stationary within the Picadilly escalator shaft and that there was a continuous outflow of air from the ticket hall to the street-level access I~ints. This is consistent with the observations by the policemen of an ou~ow of smoke at 19.37. At 19.42, Fire Brigade personnel entered the station from Pancras Road. They did not observe any smoke at this access point and, therefore, made a preliminary reconnaissance visit before setting out th~ir jets. At first sight, ~his is inconsistent with the BTP policemen's observations--if smoke had been observed then the Fire Brigade sequence of actions would probably have been different. However, Fig. 1 provides an explanation of this apparent inconsistency. Between 19.37 and 19.43, there was a continuous inflow of air from street level into the ticket hail. This would have purged the bulk of the smoke from the access points and proba~y most of the passageways and the ticket hall. From 19.41 to 19.43, air was flowing from the ticket hall down the Piccadilly escalator shaft, so that no additional smoke was entering the ticket hall. Therefore, the Fire Brigade personnel were entering along a fresh air current into a ticket h~l largely purged of smoke and with no smoke entering. Their observations of only traces of smoke were therefore understandable. During this period, BTP policemen were in control of station evacuation. They began an evacuation of the station via the Victoria line escalator towards the end of this period when the air flow was upwards in this shaft, and therefore smoke free, and the ticket hall was relatively smoke free.
7.3 Smoke production and movement, 19.43 onwards At about 19.43, conditions in the ticket hall began to deteriorate rapidly, as the atmosphere became hotter and more smoke-laden and the urgency of the evacuation procedure increased. Figure 1 shows that, at 19.43, the air flow in the Piccadilly escalator shaft switched from downwards to upwards, which would have had the effect of forcing smoke into the ticket hall; the flow in the Victoria
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escalator shaft switched to the downwards direction so that smoke was recirculated down this shaft; there was still a net inflow of fresh air into the ticket hall. Thus, the evacuation route up the Victoria escalator into the ticket hall became smoke contaminated. At 19.44, the situation changed to one in which there was a net outflow of air from the ticket hall towards street level; therefore, the linking passageways became smoke contaminated. Thus, conditions for evacuation by this route deteriorated rapidly. The above analysis is based on the prediction of Fig. 1; in fact, from 19.43-19.45, the fire was developing in size and beginning to dominate the ventilation pattern. However, this effect was in phase with the predictions of Fig. 1, since it served to increase the flow up the Piccadilly escalator shaft. Qualitatively, therefore, the combined effect would still have been a rapidly increasing air flow up this shaft. Eyewitnesses at the junction of the passageway from St Pancras Station and the ticket hall observed a rapidly changing sequence of events at about 19.44. Initially, they saw a smoky haze in the ticket hall. Conditions then became clearer but hotter for a short while, then a flow of smoke into the ticket hall began. This was a pronounced but not catastrophic flow that changed via brown, white and black in colour and oily and greasy in smell. The witnesses then turned and hurried along the passageway and were overtaken by the catastrophic flow of black smoke about half a minute later. These observations are consistent with the switch in air flow direction in the Piccadilly escalator shaft, purging the shaft of accumulated hot gases and smoke produced from different materials, such as rubber, wood, grease and plastics, and leading to the large upwards flow of smoke as the fire increased in size. At 19.45, the 'flashover' occurred and the catastrophic flow of smoke and hot gases began. This smoke flow passed along all of the passageways linking the ticket hall with street level; the actual times at which smoke flows ceased were not recorded. Within the station, the flow of smoke along passageways 1-7 soon affected the Metropolitan/Circle line platforms, which became heavily contaminated by smoke by 19.52. Trains continued to run on this line and their movement carried the smoke at least as far as Euston Square station, causing that station to be closed. Smoke also descended the Victoria line escalators (13-14) in appreciable quantities and caused serious contamination on the Victoria line platform at about 19.46 while evacuation by train was in progress.
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8 LESSONS TO BE LEARNED 8.1 Perceptions of the fire in progress As ordinary members of society, we have certain cultural perceptions of fire and the dangers associated with it. These perceptions are based on observations of controlled fires, such as bonfires or stubble burning, and on observations of accidental fires, either directly or on TV, such as warehouse fires or oil-rig fires. From these perceptions we develop an awareness of danger based on certain signs, such as large billowing flames or copious smoke emission, and a tolerance of fire situations from which such signs are absent. Clearly, these perceptions of danger differ widely between individuals. The King's Cross fire exemplifies this point. Some witnesses stopped and watched the fire shortly before flashover; one witness saw the initial entry of flame into the ticket hall and, dismissing it as a sign of immediate danger, proceeded on his way; some witnesses ran from the station at a much earlier stage, because of the presence of relatively light smoke, but felt obliged to apologise for doing so. The King's Cross fire had been burning for 15 min or so and then, within a period of 30 s or so, conditions within the ticket hall went from being somewhat hot and smoky but free from flame, to being engulfed in flames and thick, black smoke; the smoke swept through the passages to the street-level access points causing scores of people to flee for their lives. This failure to perceive the fire as a genuine threat to life, rather than a passing inconvenience, and the absence of an escape route free fron~ exposure to the smoke and fumes from the fire combined to create the conditions for a major loss of life. 8.2 The trench effect The aerodynamic effect that concentrated the fire products in the escalator trench and resulted in the rapid flame spread up the escalator came to be known as the 'trench effect'. It was an important outcome of the scientific investigation, as it demonstrated the possibility of greatly enhanced flame spread rates in some situations. Three factors combined to give this trench effect--the slope of the escalator (30°), the trench profile which affected the lateral movement of air and hot products and the presence of flammable materials on the floor and sides of this trench.
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The relative contributions of these three factors is a matter for further scientific investigation. Such questions as the effect of angle of slope on fire growth rate, the behaviour of a fire in a trench with flammable materials on the floor but not on the sides and the behaviour of materials other than wood all need to be addressed. HSE has started an investigation of some of these features, but it believes that other organisations need to consider possible situations within their areas of responsibility where the 'trench effect' might have an influence on fire growth rate and to identify research actions that might be necessary.
8.3 The behaviour of painted surfaces A crucial point to emerge in relation to the behaviour of painted surfaces in fires was the unpredictable response of paint when applied over many layers of existing paint. For Building Regulation purposes, the surface spread of flame is assessed by BS476 Pt 76 for systems to be used as internal finishes. The system comprises the substrate, e.g. plasterboard, and the decorative finish, if any, e.g. paint, and obviously tests for approval purposes are carried out on new samples. A paint can not achieve a BS476 Pt 7 classification in isolation; it must be assessed as part of a system, because its response to fire is critically dependent on its adhesion to the substrate and the properties of the substrate. The King's Cross fire concentrated attention on the behaviour of a 'real' paint system--a modern paint applied to existing paint consisting of up to 20 layers. As described in section 6.2, the trapping of solvent from the new paint had an adverse effect on the flame spread characteristics of the paint layer. This is an important point of general applicability. Fire certification requires certain standards of performance in the linings of newly constructed buildings and adherence to that standard throughout the life of the building. Maintenance of the building by painting the linings may, after some years, adversely affect flame spread properties without that effect being apparent at periodic inspections. Inspection of maintenance records, or in-situ testing of cumulative thickness of paint layers and response of sample areas of the paint to applied heat are possible responses to this problem, but more guidance on the significance of this problem in older buildings seems desirable.
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8.4 The production and movement of smoke in a complex building The King's Cross fire illustrated the speed with which smoke can be circulated in complex buildings, including recirculation into areas not necessarily in the main direction of flow of ventilation. It illustrated the confusion caused by fluctuating ventilation directions by concealing the location, or indeed the existence, of a fire from Fire Brigade personnel on arrival. The paramount importance of supplying detailed and reliable information to the Fire Brigade immediately on arrival was underlined. Above all, the fire illustrated once more the supreme importance of the provision of smoke-free routes. Most of the fatalities were caused by exposure to smoke; many survivors had to flee for their lives through hot, dense smoke. There are two complementary approaches to this problem--the reduction of smoke emission in the event of a fire, and the isolation of escape routes from any smoke that is produced in a fire (and, of course, for life safety, that includes isolation from exposure to carbon monoxide and other toxic gases). Assessment of materials must take account not only of flammability characteristics but also of smoke-producing characteristics. Continuing attention to smoke production potential of materials is vital. The regions of the station affected by smoke once flashover had occurred are illustrated in Fig. 2. Some recirculation of smoke occurred to levels lower than the seat of the fire, e.g. the Victoria line platforms. All levels above the seat of the fire in the main line of flow were smoke logged, including the Metropolitan/Circle line. Many people were evacuated via Victoria line trains, and the passageway 6-19-20-21 to King's Cross Thameslink station remained smoke-free throughout (it was not used for evacuation initially because all access gates were locked). However, it was not physically isolated by smoke-control doors; it remained smoke-free because of its position in the ventilation circuit, as shown in Fig. 2. If the fire had occurred towards the bottom of the Piccadilly escalator, at node 23 say, then the flow of smoke on to the Victoria line platforms would have been greater, and it is then likely that smoke flow along the platform from 14 to 19 would have affected this passageway as well If the fire had occurred on the similar (though shorter) escalator from the Northern line platforms (17-18), at node 24, say, then the Victoria line and Piccadilly line platforms would have been heavily contaminated by smoke, as would the passageway to King's Cross Thameslink. It
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is possible that the Northern line platforms would have been contaminated as well, which would have left the entire station smoke contaminated and with no smoke-free escape routes. The King's Cross fire re-emphasised the necessity, when considering emergency plans for evacuation from complex buildings in the event of a fire, to have a clear idea of likely smoke flow routes and their effect on means of escape. One needs some equivalent ventilation circuit to predict these routes, or alternative means of predicting smoke flows.
REFERENCES 1. Fenneli, D., Investigation into the King's Cross Fire. HMSO, London, UK, 1988. 2. Moodie, K., The King's Cross Fire: Damage assessment and overview of the technical investigation. Fire Safety J., 18(1) (1992) 13-33. 3. Crossland, B., The King's Cross Fire and the setting up of the investigation. Fire Safety J., 18(1) (1992) 3-11. 4. Wharton, R. K., Studies relating to ignition of the fire at King's Cross Underground Station. Fire Safety J., 18(1) (1992) 35-47. 5. Moodie, K. & Jagger, S. F., The King's Cross Fire: Results and analysis from the scale model tests. Fire Safety J., 18(1) (1992) 83-103. 6. British Standard Institution, BS476 Pt 7. Method for classification of the surface spread of flame of products, 1987.
The King's Cross Fire: A Correlation of Eyewitness Accounts and Results of the Scientific Investigation* A. F. Roberts~ Health and Safety Executive, Buxton, Derbyshire, SK17 9JN, UK
ABSTRACT During the 15-rain period, or thereabouts, between the first observation of the fire and its fatal eruption into the ticket hall, the fire at King's Cross Underground Station was observed by many witnesses. Naturally, their descriptions differed appreciably in points of detail, but, overall, they led to a reasonably consistent picture of the fire's development. This picture provided a vital frame of reference against which scientific description of possible sequences of fire development could be tested, particularly with respect to the last 1 or 2 rain prior to fire spread into the ticket hall. This paper presents the frame of reference provided by eyewitness accounts and the correlation with the outcome of the scientific investigation. 1 INTRODUCTION On Wednesday 18 November 1987, at approximately 19.30, the presence of a small fire on escalator No. 4 at the King's Cross Underground station was first reported. This fire developed relatively slowly for over 10min, but, shortly before 19.45, it began to develop much more quickly. At approximately 19.45, flames spread with cvasiderable rapidity into the ticket hall at the top of the escalator and * Paper presented at the I. Mech. E. seminar 'The King's Cross Underground Fire: Fire Dynamics and the Organisation of Safety', 1st June 1989. ~Present address: Nuclear Safety Research Management Unit, Health and Safety Executive, Broad Lane, Sheltield, S3 7HQ, UK.
105 (~) 1991 Crown Copyright.
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large quantities of thick, black smoke developed, spreading along all the passageways leading to street level exits. Scores of people had to flee for their lives through this smoke, and 31 people died as a result of the fire. The Public Investigation under Mr Desmond Fennell QC ~ heard evidence from many eyewitnesses of the different stages of the development of the fire. As with any body of eyewitness evidence, there were differences of emphasis and description and some anomalies, but there was also sufficient consensus for a reasonably reliable and detailed description of the fire's behaviour to emerge. The logs of the control centres of London Fire Brigade and British Transport Police and records of train movements on the London Underground system and at British Rail's St Pancras were used to provide time estimates for eyewitness evidence. Therefore, it was possible to construct not only a qualitative description but also a reasonably consistent chronology for the sequence of events. This detailed chronology provided an essential reference framework for the scientific investigation, in particular with respect to the rapidity of the fire's development at the time of entry of flames into the ticket hall. In comparing the eyewitness evidence with the findings of the scientific investigation, three areas of interest will be considered:
(1) (2) (3)
the initiation of the fire; the growth of the fire above the escalator, up to flashover; and smoke production and movement.
However, in order to put these comparisons into a context, some problems relating to eyewitness evidence will be considered and brief details of the station given. 2 PROBLEMS WITH EYEWITNESS EVIDENCE Apart from the normal problems with eyewitness evidence, deriving from the variability of human perception and recall of events, there were some additional complicating features at the King's Cross fire. The affected escalator was essentially a trench some 1.2m wide, 0.8 m deep and 40 m long, inclined at 30* to the horizontal. When viewing from either end, it was possible to make a reliable estimate of position in the nearer half of the escalator, but perspective effects make such estimates unreliable in the further half of the escalator; also eyewitnesses' perception of flames and smoke was substantially affected by viewing position. In particular, as it transpired, an eyewitness on
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escalator No. 6, looking across the escalator shaft, could only see the top of the trench of escalator No. 4. Low-lying flames within the escalator trench were obscured from view and attention was concentrated on flames emerging from the escalator trench. Eyewitnesses of the entry of flame into the ticket hail experienced a rapidly developing sequence of events. Initial descriptions differed appreciably as one witness concentrated on one 'frame' in the sequence and another on a different frame. Not surprisingly, not one witness was able to give a continuous and coherent account of the sequence of events, but the cumulative effect of their evidence gave a reasonably consistent picture.
3 STA'FION LAYOUT A full description of the station layout is given in the report of the Investigation ~ and a summary account is given in the papers by Moodie 2 and Crossland; 3 therefore, details are not reported here.
4 VENTILATION ARRANGEMENTS AT THE STATION The main source of ventilation at King's Cross station was air movements caused by the movement of trains. An Underground train fills an appreciable fraction of the cross-section of the running tunnels and causes a piston effect. The approach of a train drives air into the station and the departure sucks air out. This clearly gives rise to rapid fluctuations in air velocity throughout the station complex. The requirement is for four air changes per hour, with air velocities not exceeding 6.7 m/s on escalators aad stairways and 4.5 m/s in ticket halls. At King's Cross station there were two exhaust-fan ventilation shafts and two draught-relief shafts; details of these are given in Appendix I of the report of the Investigation. ~ A computation of the air velocities in the Piccadilly line escalator shaft and in the Victoria line escalator shaft for the period 19.30-19.50 on the night of the fire is shown in Fig. 1. This computation was based on the known layout of the station and the logged train movements in that period; it took no account of possible interfering effects of the developing fire. The cross-sectional areas of both escalator shafts are the same so that the algebraic sum of the two velocities gives a velocity proportional to
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3
A W
l :I
II .o_ 13
PICCADILLY LINE ESCALATOR SHAFT
2 1 0 -1 -2 -3
VICTORIA LINE ESCALATOR SHAFT
I:
÷ J~ E
NET AIR FLOW INTO TICKET HALL FROM ESCALATOR SHAFTS
>o ?-
-2 -3
19,30 19,32 19.34 19.36 19.35 19.40 19.42 19.44 19.46 19.48 19.50 Time
Fig. 1. Computed air velocities. NB The computation neglects the buoyancy effects of the fire, which would become dominant after 19.45. (See Fig. 17 of Ref. 1).
the net air flow from the two shafts into the ticket hall; this net velocity is also shown on Fig. 1. 5 THE INITIATION OF THE FIRE At about 19.30, several passengers travelling upwards on escalator No. 4 towards the ticket hall observed signs of fire beneath the escalator. Within the next 2-3 min the escalator was stopped, station staff were informed and a member of the British Transport Police (BTP), who happened to be in the ticket hall at the time, sent a radio message to the BTP control room requesting attendance by London Fire Brigade (logged at 19.33). The general experience of passengers travelling up escalator No. 4 while it was still moving, was that the signs of fire began about half way up on the right-hand side (looking up). Witnesses variously reported experiencing hot air or smoke above the escalator or seeing signs of flames or glowing beneath the escalator, via minor gaps between steps or between the moving steps and the stationary side of the escalator. Several witnesses spoke of seeing flames or sparks at more than one place beneath the escalator, possibly moving with the escalator.
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After escalator No. 4 was shut down, several other witnesses using escalator Nos 5 or 6 saw smoke or flames at more than one location. For example, at about 19.40, a witness walking up escalator No. 6 recalled seeing the reflections of flames half way up escalator No. 4 and again about three-quarters of the way up. The detailed examination of the scene of the fire, reported by Moodie, 2 showed that the lowest point of fire damage was on the right-hand running track of escalator No. 4 at a point adjacent to step 48 (counting from the bottom of the escalator, which had 101 steps visible). Ignition tests and the in-situ fire test showed the ease with which the layer of grease and detritus on the running track of the escalator could be ignited by a small flame, such as that on a burning match, to give an effect similar to that reported by eyewitnesses? The eyewitness evidence and the scientific evidence, therefore, agree on the initiation of the fire being beneath the escalator, at a point about half-way up on the right-hand side. There was no direct material evidence for the existence of more than one point of initiation, but there is strong eyewitness evidence for the establishment of a second seat of fire about three-quarters of the way up the escalator. Such multiple seats of fire are known from previous escalator fires and have been attributed to the spread of fire by burning material on the escalator chain, prior to the stopping of the escalator. This explanation is consistent with some eyewitness accounts. In the in-situ fire test the escalator was stationary, and in the actual fire conclusive material evidence of a second seat of initiation above step 48 would have been destroyed, so the lack of material evidence is not surprising.
6 THE GROWTH OF THE FIRE
6.1 19.30-19.43 At 19.32, a BTP policeman and a London Underground employee went down the stationary escalator No. 4 to inspect the fire. At that time, flames were just beginning to emerge from the gap between the stairs and the sides of the escalator over a length of about one step; this compares with the state of the in-situ fire test at about the 6-7 min stage, suggesting an ignition time of about 19.25. At 19.38, two further BTP policemen looked down escalator No. 4 from the ticket hall. They observed the fire as mainly on one side and stretching about half-way across the width of the escalator over one or
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two steps. The fire was clean burning, flames were about handrail height and the position of the fire was estimated at about half-way down.
In the period up to 19.43, other witnesses made somewhat similar observations, suggesting that the fire was established but developing rather slowly, in a manner consistent with the Health and Safety Executive (HSE) trials on a six-step section of escalator. Figure 1 shows that in the period 19.34-19.43, the air flow in this escalator shaft was either very low or was in a downwards direction. Therefore, it was not assisting the growth of the fire; if anything, it was restricting it. 6.2 19.43-19.46
In this period, it may be helpful to put estimated times to the nearest 15 s. These estimates are based on logged times of radio messages, estimates of travelling times from one point to another, etc. They are not highly accurate, but they do serve to give a feeling of the time-scale of a rapidly developing sequence of events. 19.42.45 Two fire appliances arrive and park in Pancras Road. Station Officer Townsley and Temporary Sub-Officer Bell enter station. 19.43.30 Townsley and Bell arrive at top of escalator No. 4 and confer. Townsley remains in charge in ticket hall, Bell descends escalator No. 6 to take charge below. 19.44.30 Bell arrives at bottom of escalator. 19.45.15 Mr Bates, a passenger, arrives in ticket hail. Mr Bates, PC Hanson and many others are suddenly exposed to smoke and flames. 19.46.00 PC Hanson is led to safety by PC Dixon at Euston Road (south) access point. There were, of course, many other observations complementary to these; they are broadly consistent with the above framework. On entering the ticket hall, Bell found it somewhat hot and smoky but not seriously so (19.43.30). On descending escalator No. 6, he looked across to escalator No. 4 and saw flames above the level of the handrail, bright and clear burning, comparable to those produced by the burning of a large cardboard box (19.44.15). On reaching the bottom of the escalator and looking up escalator No. 4, he saw flames on the hoarding on the left-hand side of the escalator shaft, having spread from the trench of escalator No. 4 (19.44.30).
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Three firemen looked down escalator No. 4 shortly after Bell left the ticket hall and reported seeing flames across the escalator, about 4 ft high and about one-third of the way down. They reported that there was not very much smoke from the fire (19.44.00). Three passengers, who were turned away from the foot of escalator No. 4 by Bell, reported seeing flames hallway up escalator No. 4, 5-6 ft high and 4-5 yards long, with flames shooting from both sides of the escaiator. (19.44.30). Bates entered the ticket hall from the Victoria line escalator at 19.45.15. He saw a relatively small flame at the top of escalator No. 4, between floor level and about 3 ft above the floor; he continued to make his escape across the ticket hall, but within a few seconds he experienced flames sweeping across the ticket hall towards him, accompanied shortly afterwards by thick, black smoke. PC Hanson, at about the same time, saw a jet of flame emerge from the top of escalator No. 4 and strike the ticket-hall ceiling. On the escalator side of the jet of flame, he could see unburnt ceiling; as the jet hit the ceiling, it turned into a layer of flame that rapidly spread outwards beneath the ceiling. Very shortly afterwards, massive quantities of clark smoke began to appear. Other eyewitnesses, mainly near the top of the Victoria line escalators, gave similar descriptions of a layer of flame spreading beneath the ceiling, hitting the side wall near the Victoria line escalator and being deflected downwards, filling in between the original layer and the floor, and the more or less simultaneous appearance of thick, black smoke. The 'best guess' is that a period of about 45 s elapsed between the fire beginning to develop strongly on the escalator (19.44.30) and flames entering the ticket hall (19.45.15). The eyewitness accounts show that even as the flames entered, there was relatively little smoke in the ticket hall---the massive flow of smoke came a few seconds after the entry of flame. The scientific investigation and the..',aking of statements began immediately after the fire, but much of the above details only began to emerge in cross examination. Essentially, a coherent eyewitness account was not available until March 1988, when the very short time interval of 45 s referred to ia the previous paragraph began to seem likely. Two schools of thought were apparent at that time--those who propounded flame spread predominantly on the escalator, and those who propounded rapid flame spread along the painted ceiling. The eyewitness evidence of Bates and Hanson strongly favoured the former,
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but no scientific witness at that time could produce a convincing explanation to meet the 45 s requirement. The Harwel! computations (presented in June 1988), experiments at Edinburgh University (July 1988) and the HSE model tests (carried out in July and August 1988) did provide the required convincing explanation. As the paper by Moodie and Jagger 5 shows, the 'trench effect' evident in the Harwell computations becomes established when flames involve both sides and the steps of the escalator trench; a fire that is involving a length of perhaps only two steps then begins to increase in length at a more or less exponential rate. As stated earlier, it seems likely that two independent seats of burning developed on escalator No. 4, the lower one near step 48 (about half-way up) and the other about three-quarters of the way up. In the ~3-scale model tests, once the trench effect had developed, the flame front spread from the half-way height to the ticket hall in 30-45 s. As fac as one can judge at this stage, the time-scale for flame spread in tl" models is not a function of linear scale, i.e. it can be related to a dimensionless distance scale. If this is so, then either position for the main seat of the fire, i.e. the one where the trench effect first developed, provides a satisfactory explanation of the 45-s interval before flames spread into the ticket hall. The trench effect provides a good explanation of the rate at which the flame spread in the upper part of the escalator. It also provides three additional points of agreement with eyewitness evidence.
(1)
(2)
The model tests showed a sequence of events as the flames entered the ticket hall that bears a close resemblance to the 'frames' from the sequence described by Bates, Hanson and others. The fire on the woodwork of the escalator burnt with very little smoke. Even when this fire was well developed, little smoke entered the model ticket hall, as appeared to be the case on the
night.
(3) The fire in the model kept very low and it was hard to assess its full dimensions from any one viewing point~ From the side, most of it was obscured by the sides of the escalator, and, from normal viewing positions at the ends of the trench, perspective effects limited the impression of size. Therefore, many puzzling aspects of the fire--its rate of spread, the relative lack of smoke before flashover, the lack of alarm in many of those witnessing it--stem from the trench effect. The interaction between the growth of the fire and the imposed
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ventilation is of interest. Figure 1 indicates that the air flow was downwards in the Piccadilly line escalator shaft from 19.40.30 to 19.43.30, thereby restricting the rate of growth of the fire. At 19.43.30, the flow switched to the upwards direction, reaching 2.9m/s by 19.44.30. This is the period during which the fire began its rapid accelertion up the escalator shaft. It may be that the change in air-flow condi~:ions from 19.43 onwards facilitated the development of the trench effect by removing an effect that was tending to keep the flames upright and substituting an effect that was tending to deflect the flames down into the escalator trench. Once the fire had begun to develop rapidly, its buoyancy effects would dominate the air flow pattern, and, from 19.45 onwards, the flow of air in the Piccadilly line escalator shaft was consistently upwards. On approaching the throat of the escalator shaft, as it enters the ticket hall, flames from the escalator trench spilled out to involve the whole cross-section of the shaft. This immediately exposed additional materials to fire attack--rubber, plastic, paint. The early stages of this attack may have been observed by some witnesses at the edge of the ticket hall who observed an increase in smoke flow, with changing sequence of colours, prior to the main smoke flow. It seems likely that the main smoke flow derived from the painted ceiling in the escalator shaft and in the ticket hail, as large surface areas of paint were suddenly exposed to a large heat source. The study of the painted ceiling in the escalator shaft was restricted by the complexity of the paint system. Accurate simulation of it was impossible. Only relatively small amounts of the actual paint system could be removed, adhered to its substrate, for examination. The indications from this examination were that, although fire was capable of spreading across the surface much more rapidly than if the paint had adhered to the substrate properly, the development of the ceiling fire was not rapid enough to make any major contribution to the sudden growth of the fire. It would appear that the trench effect is sufficient to account for the speed of development. On the other hand, it did appear likely that this paint system and other painted areas could have accounted for the sudden production of smoke. The deterioration in fire performance was shown to derive from the application of a modern, high-build paint system (six coats) to old paint, giving about 20 layers in total. Solvent from the most recently applied system was trapped to some extent in the old layers; the application of heat from the fire created solvent vapours, which blew large blisters in the upper paint layers.
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This delamination of the upper layers made the paint much more vulnerable to burning and created the increase in rate of flame spread that was observed in the tests. 6.3 19.46 onwards From 19.46 onwards, the fire was fully established in the Piccadilly line escalator shaft, where approximately 3.2 tonnes of material (mainly wood) burned in the main seat of the fire. Approximately 0.75 tonnes of material (mainly wood) burned in the ticket hail. In this phase, the fire burned as one would expect, with a large quantity of wood in an inclined shaft. The search-and-rescue operation and the fire-control operation of the London Fire Brigade dominated this period, and these are comprehensively described in Chapter 11 of the report of the Investigation. 1
7 SMOKE PRODUCTION AND MOVEMENT 7.1 An equivalent ventilation circuit for the station In order to gain an understanding of the movement of smoke during the fire, it is necessary to consider a representative ventilation circuit for the station; a full description would be very complex, but the main features of such a circuit are represented in Fig. 2. This schematic representation shows the six main levels of the station, using street level as a reference plane. Distance below street level (m) • approx. 6
Regl smoke 19 r
L
STREET LEVEL TUBE TICKET HALL LEVEL METROPOLITAN/CIRCLELINE LEVEL
0 4 7
SEAT OF FIRE
13
VICTORIA LINE LEVEL
16
PICCADILLY LINE LEVEL
21
NORTHERN LINE LEVEL
27
Fig. 2. An equivalent ventilation circuit (exhaust-fan shafts, draft-relief shafts and cross-passages omitted). Nodes 1-21 represent the junctions of airways; nodes 22-24 the actual and hypothetical seats of fire; 13-14, 15-16 and 17-18 the escalator shafts; and 6-19-20-21 the passageway to King's Cross Thameslink station.
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The five access points to street level from the ticket halls are denoted by nodes 1-5 (representing Euston Road (south), Euston Road (north), Pancras Road, St Pancras BR station and King's Cross BR station, respectively). A sixth access point to street level (node 6) was in the King's Cross Thameslink station. NodesT-10 represent the passageways leaving the tube ticket hall for the street-level access points. The passageway from 7 served access points 1 and 2, and a side passage (11) led to the Metropolitan/Circle line ticket hall at 12. The escalator shaft between the Victoria line and the ticket hall is represented by 13-14; the escalator shaft between the Piccadilly line and the ticket hall is represented by 15-16; and the escalator shaft between the Northern line and the Piccadilly line is represented by 17-18. The independent passageway from the tube platforms to King's Cross Thameslink Station is represented by 6-19-20-21. Other passageways, exhaust-fan shafts and draught-relief shafts are omitted for the sake of simplicity. The fire started at node 22 in escalator shaft 15-16, at approximately 12 m below street level. As stated in section 4, the driving force for the ventilation in normal circumstances was mainly provided by the movement of trains along the various lines, providing fluctuating air velocities throughout the station with some net air exchange between the station and the external atmosphere. When the fire started it remained relatively small until 19.43. However, as it rapidly grew from 19.43 onwards, it began to develop significant buoyancy forces in the escalator shaft 15-16. With the site of the fire 12 m below street level, the developed fire would have had a dominating effect on air movements, with a strong updraught in 15-16, lateral spread in the ticket hall (7-8-9-10), some downwards recirculation of air from the ticket hall into 13-14, and strong outflows in the passages between the ticket hall arid street level.
7.2 Smoke production and movement, 19.30-19.43 There was relatively little smoke production in this period. Some eyewitnesses reported discomfort or panic from the presence of smoke, but most reported no more than traces of smoke. As early as 19.35, a London Underground technician experienced smoke at the foot of the Victoria escalator (14); the route for this smoke movement is likely to have been up 15-16 and down 13-14, via
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the ticket hall. Figure 1 shows that, between 19.32 and 19.34, the air flow was up the Piccadifiy escalator shaft and down the Victoria escalator shaft, which is consistent with this view. At 19.37, two BTP policemen entered the station at the Euston Road (north) entrance (node 2 on Fig. 2) and observed white smoke issuing at this point. Figure 1 shows that, between 19.32 and 19.37, the air flow was either upwards or virtually stationary within the Picadilly escalator shaft and that there was a continuous outflow of air from the ticket hall to the street-level access I~ints. This is consistent with the observations by the policemen of an ou~ow of smoke at 19.37. At 19.42, Fire Brigade personnel entered the station from Pancras Road. They did not observe any smoke at this access point and, therefore, made a preliminary reconnaissance visit before setting out th~ir jets. At first sight, ~his is inconsistent with the BTP policemen's observations--if smoke had been observed then the Fire Brigade sequence of actions would probably have been different. However, Fig. 1 provides an explanation of this apparent inconsistency. Between 19.37 and 19.43, there was a continuous inflow of air from street level into the ticket hail. This would have purged the bulk of the smoke from the access points and proba~y most of the passageways and the ticket hall. From 19.41 to 19.43, air was flowing from the ticket hall down the Piccadilly escalator shaft, so that no additional smoke was entering the ticket hall. Therefore, the Fire Brigade personnel were entering along a fresh air current into a ticket h~l largely purged of smoke and with no smoke entering. Their observations of only traces of smoke were therefore understandable. During this period, BTP policemen were in control of station evacuation. They began an evacuation of the station via the Victoria line escalator towards the end of this period when the air flow was upwards in this shaft, and therefore smoke free, and the ticket hall was relatively smoke free.
7.3 Smoke production and movement, 19.43 onwards At about 19.43, conditions in the ticket hall began to deteriorate rapidly, as the atmosphere became hotter and more smoke-laden and the urgency of the evacuation procedure increased. Figure 1 shows that, at 19.43, the air flow in the Piccadilly escalator shaft switched from downwards to upwards, which would have had the effect of forcing smoke into the ticket hall; the flow in the Victoria
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escalator shaft switched to the downwards direction so that smoke was recirculated down this shaft; there was still a net inflow of fresh air into the ticket hall. Thus, the evacuation route up the Victoria escalator into the ticket hall became smoke contaminated. At 19.44, the situation changed to one in which there was a net outflow of air from the ticket hall towards street level; therefore, the linking passageways became smoke contaminated. Thus, conditions for evacuation by this route deteriorated rapidly. The above analysis is based on the prediction of Fig. 1; in fact, from 19.43-19.45, the fire was developing in size and beginning to dominate the ventilation pattern. However, this effect was in phase with the predictions of Fig. 1, since it served to increase the flow up the Piccadilly escalator shaft. Qualitatively, therefore, the combined effect would still have been a rapidly increasing air flow up this shaft. Eyewitnesses at the junction of the passageway from St Pancras Station and the ticket hall observed a rapidly changing sequence of events at about 19.44. Initially, they saw a smoky haze in the ticket hall. Conditions then became clearer but hotter for a short while, then a flow of smoke into the ticket hall began. This was a pronounced but not catastrophic flow that changed via brown, white and black in colour and oily and greasy in smell. The witnesses then turned and hurried along the passageway and were overtaken by the catastrophic flow of black smoke about half a minute later. These observations are consistent with the switch in air flow direction in the Piccadilly escalator shaft, purging the shaft of accumulated hot gases and smoke produced from different materials, such as rubber, wood, grease and plastics, and leading to the large upwards flow of smoke as the fire increased in size. At 19.45, the 'flashover' occurred and the catastrophic flow of smoke and hot gases began. This smoke flow passed along all of the passageways linking the ticket hall with street level; the actual times at which smoke flows ceased were not recorded. Within the station, the flow of smoke along passageways 1-7 soon affected the Metropolitan/Circle line platforms, which became heavily contaminated by smoke by 19.52. Trains continued to run on this line and their movement carried the smoke at least as far as Euston Square station, causing that station to be closed. Smoke also descended the Victoria line escalators (13-14) in appreciable quantities and caused serious contamination on the Victoria line platform at about 19.46 while evacuation by train was in progress.
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8 LESSONS TO BE LEARNED 8.1 Perceptions of the fire in progress As ordinary members of society, we have certain cultural perceptions of fire and the dangers associated with it. These perceptions are based on observations of controlled fires, such as bonfires or stubble burning, and on observations of accidental fires, either directly or on TV, such as warehouse fires or oil-rig fires. From these perceptions we develop an awareness of danger based on certain signs, such as large billowing flames or copious smoke emission, and a tolerance of fire situations from which such signs are absent. Clearly, these perceptions of danger differ widely between individuals. The King's Cross fire exemplifies this point. Some witnesses stopped and watched the fire shortly before flashover; one witness saw the initial entry of flame into the ticket hall and, dismissing it as a sign of immediate danger, proceeded on his way; some witnesses ran from the station at a much earlier stage, because of the presence of relatively light smoke, but felt obliged to apologise for doing so. The King's Cross fire had been burning for 15 min or so and then, within a period of 30 s or so, conditions within the ticket hall went from being somewhat hot and smoky but free from flame, to being engulfed in flames and thick, black smoke; the smoke swept through the passages to the street-level access points causing scores of people to flee for their lives. This failure to perceive the fire as a genuine threat to life, rather than a passing inconvenience, and the absence of an escape route free fron~ exposure to the smoke and fumes from the fire combined to create the conditions for a major loss of life. 8.2 The trench effect The aerodynamic effect that concentrated the fire products in the escalator trench and resulted in the rapid flame spread up the escalator came to be known as the 'trench effect'. It was an important outcome of the scientific investigation, as it demonstrated the possibility of greatly enhanced flame spread rates in some situations. Three factors combined to give this trench effect--the slope of the escalator (30°), the trench profile which affected the lateral movement of air and hot products and the presence of flammable materials on the floor and sides of this trench.
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The relative contributions of these three factors is a matter for further scientific investigation. Such questions as the effect of angle of slope on fire growth rate, the behaviour of a fire in a trench with flammable materials on the floor but not on the sides and the behaviour of materials other than wood all need to be addressed. HSE has started an investigation of some of these features, but it believes that other organisations need to consider possible situations within their areas of responsibility where the 'trench effect' might have an influence on fire growth rate and to identify research actions that might be necessary.
8.3 The behaviour of painted surfaces A crucial point to emerge in relation to the behaviour of painted surfaces in fires was the unpredictable response of paint when applied over many layers of existing paint. For Building Regulation purposes, the surface spread of flame is assessed by BS476 Pt 76 for systems to be used as internal finishes. The system comprises the substrate, e.g. plasterboard, and the decorative finish, if any, e.g. paint, and obviously tests for approval purposes are carried out on new samples. A paint can not achieve a BS476 Pt 7 classification in isolation; it must be assessed as part of a system, because its response to fire is critically dependent on its adhesion to the substrate and the properties of the substrate. The King's Cross fire concentrated attention on the behaviour of a 'real' paint system--a modern paint applied to existing paint consisting of up to 20 layers. As described in section 6.2, the trapping of solvent from the new paint had an adverse effect on the flame spread characteristics of the paint layer. This is an important point of general applicability. Fire certification requires certain standards of performance in the linings of newly constructed buildings and adherence to that standard throughout the life of the building. Maintenance of the building by painting the linings may, after some years, adversely affect flame spread properties without that effect being apparent at periodic inspections. Inspection of maintenance records, or in-situ testing of cumulative thickness of paint layers and response of sample areas of the paint to applied heat are possible responses to this problem, but more guidance on the significance of this problem in older buildings seems desirable.
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8.4 The production and movement of smoke in a complex building The King's Cross fire illustrated the speed with which smoke can be circulated in complex buildings, including recirculation into areas not necessarily in the main direction of flow of ventilation. It illustrated the confusion caused by fluctuating ventilation directions by concealing the location, or indeed the existence, of a fire from Fire Brigade personnel on arrival. The paramount importance of supplying detailed and reliable information to the Fire Brigade immediately on arrival was underlined. Above all, the fire illustrated once more the supreme importance of the provision of smoke-free routes. Most of the fatalities were caused by exposure to smoke; many survivors had to flee for their lives through hot, dense smoke. There are two complementary approaches to this problem--the reduction of smoke emission in the event of a fire, and the isolation of escape routes from any smoke that is produced in a fire (and, of course, for life safety, that includes isolation from exposure to carbon monoxide and other toxic gases). Assessment of materials must take account not only of flammability characteristics but also of smoke-producing characteristics. Continuing attention to smoke production potential of materials is vital. The regions of the station affected by smoke once flashover had occurred are illustrated in Fig. 2. Some recirculation of smoke occurred to levels lower than the seat of the fire, e.g. the Victoria line platforms. All levels above the seat of the fire in the main line of flow were smoke logged, including the Metropolitan/Circle line. Many people were evacuated via Victoria line trains, and the passageway 6-19-20-21 to King's Cross Thameslink station remained smoke-free throughout (it was not used for evacuation initially because all access gates were locked). However, it was not physically isolated by smoke-control doors; it remained smoke-free because of its position in the ventilation circuit, as shown in Fig. 2. If the fire had occurred towards the bottom of the Piccadilly escalator, at node 23 say, then the flow of smoke on to the Victoria line platforms would have been greater, and it is then likely that smoke flow along the platform from 14 to 19 would have affected this passageway as well If the fire had occurred on the similar (though shorter) escalator from the Northern line platforms (17-18), at node 24, say, then the Victoria line and Piccadilly line platforms would have been heavily contaminated by smoke, as would the passageway to King's Cross Thameslink. It
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is possible that the Northern line platforms would have been contaminated as well, which would have left the entire station smoke contaminated and with no smoke-free escape routes. The King's Cross fire re-emphasised the necessity, when considering emergency plans for evacuation from complex buildings in the event of a fire, to have a clear idea of likely smoke flow routes and their effect on means of escape. One needs some equivalent ventilation circuit to predict these routes, or alternative means of predicting smoke flows.
REFERENCES 1. Fenneli, D., Investigation into the King's Cross Fire. HMSO, London, UK, 1988. 2. Moodie, K., The King's Cross Fire: Damage assessment and overview of the technical investigation. Fire Safety J., 18(1) (1992) 13-33. 3. Crossland, B., The King's Cross Fire and the setting up of the investigation. Fire Safety J., 18(1) (1992) 3-11. 4. Wharton, R. K., Studies relating to ignition of the fire at King's Cross Underground Station. Fire Safety J., 18(1) (1992) 35-47. 5. Moodie, K. & Jagger, S. F., The King's Cross Fire: Results and analysis from the scale model tests. Fire Safety J., 18(1) (1992) 83-103. 6. British Standard Institution, BS476 Pt 7. Method for classification of the surface spread of flame of products, 1987.