Characterisation of open-door electrical cabinet fires in compartments

Nuclear Engineering and Design 286 (2015) 104–115

Contents lists available at ScienceDirect

Nuclear Engineering and Design journal homepage: www.elsevier.com/locate/nucengdes

Characterisation of open-door electrical cabinet fires in compartments M. Coutin ∗ , W. Plumecocq, P. Zavaleta, L. Audouin Institut de Radioprotection et de Sûreté Nucléaire (IRSN), BP n◦ 3, St Paul-Lez-Durance Cedex 13115, France

h i g h l i g h t s • Heat release rate of electrical cabinet fire source in a vitiated atmosphere. • Experimental database for proper validation the combustible modelling, taking into account the oxygen depletion in an enclosure. • New model for complex fire source.

a r t i c l e

i n f o

Article history: Received 17 July 2014 Received in revised form 27 January 2015 Accepted 29 January 2015

a b s t r a c t The study of electrical fires is a major concern for fire safety in the industry and more particularly for fire safety in nuclear facilities. To investigate this topic, IRSN conducted a large number of real-scale experiments involving open-door electrical cabinets burning firstly under a calorimetric hood and then inside a mechanically-ventilated compartment. The main challenges are to determine accurately the heat release rate of such a complex fire source in a vitiated atmosphere and to provide an experimental database for validating properly the combustible modelling, taking into account the oxygen depletion in an enclosure. After providing a detailed description of the fire scenarios and of the experimental apparatus, this paper focuses on the characteristic stages of the cabinet fire development, essentially based on the heat release rate time evolution of the fire. The effects of the confinement, of the outlet branch location, of the ventilation management and of the fire barrier on the fire source were then investigated. The reproducibility of electrical cabinet fires is also studied. A new model for complex fire source (applied in this study for open-door electrical cabinet fires) was then developed. This model was introduced in the zone code SYLVIA and the major features of the compartment fire experiments, such as characteristic heat release rate with effect of oxygen depletion and over-pressure peak were then calculated with a rather good agreement for this complex fire source (i.e. electrical cabinet). © 2015 Elsevier B.V. All rights reserved.

1. Introduction The study of electrical fires is a major concern for fire safety in the industry and more particularly for fire safety in Nuclear Power Plants (NPP) and in Nuclear Reprocessing Plants (NRP). In NPP’s, the fire hazard could cause severe consequences on safety functions inside the fire compartment and furthermore could lead to the loss of one or several compartments (switchgear room, room for electrical control equipment, battery room, etc.). The fire consequences could also involve structural damage on NPP until significant impact on safety trains (Werner et al., 2009) and then on the control of the reactor. In NRP’s, the main concerns are to avoid the release of radioactive materials inside and outside of the

∗ Corresponding author. Tel.: +33 442 199 480; fax: +33 442 199 163. E-mail address: [email protected] (M. Coutin). http://dx.doi.org/10.1016/j.nucengdes.2015.01.017 0029-5493/© 2015 Elsevier B.V. All rights reserved.

NRP due to a fire event. From the OECD FIRE Database (Werner et al., 2009, 2011), a majority of the fire ignition is due to electrical sources (close to 50%), as seen in Fig. 1. More specifically, a significant contributor to this electrical fire hazard is attributed to electrical or electronic cabinets, with an occurrence of more than 10% of all fire events (i.e., 344 events, see Fig. 1), including all types of electrical cabinet (low, medium and high voltage), as shown in Fig. 2. The handling of such fire sources in fire safety applications (i.e., performing calculations of fire scenarios for instance) is not obvious, however. The first reason for the difficulty encountered in this area lies in the complexity of this type of fire source:

• the heterogeneous composition of the fire source, with many types of plastic materials (for instance, thermoplastics and thermoset polymers),

M. Coutin et al. / Nuclear Engineering and Design 286 (2015) 104–115

105

Nomenclature Acronyms C soot CH4 methane CO carbon monoxide CO2 carbon dioxide water vapour H2 O HRR heat release rate MLR mass loss rate oxygen O2 PXA3 PICSEL A.3.1 PXA3b PICSEL A.3.2 PXR3 PICSEL R.3 PXR3b PICSEL R.3bis PICSEL V.1 PXV1 PXV2 PICSEL V.2 PXS0 PICSEL S.0 PICSEL S.1 PXS1 PICSEL S.2 PXS2 Symbols duration [s] d ˙∞ mass loss rate [kg s−1 ] m Q˙ heat release rate [W] time [s] t X volume fraction [–] Greek letters Hc effective heat of combustion [J kg−1 ] Hc∞ effective heat of combustion under well ventilated conditions [J kg−1 ] heat released by oxygen consumption [J kg−1 ] HO2 ˇ correction factor [–] oxygen-limiting law [–]   coefficient of the reaction of combustion [–] rate [%]  Subscripts ∞ ambient Incub incubation stage

Fig. 1. Ignition sources/mechanisms (Werner et al., 2009).

(Melis and Audouin, 2008; Suard et al., 2011) is necessary to consider the decrease of HRR and the related mass loss rate as the oxygen concentration decreases within the fire compartment (eventually until the fire becomes extinguished due to excessively low oxygen concentration). During fire experiments in compartments, the challenge is mainly to determine the full scale heat release rate of complex fire sources in a vitiated atmosphere (Babrauskas and Grayson, 1996; Hamins et al., 2008) and to provide an experimental database for validating the fire source modelling properly, taking into account the oxygen depletion in an enclosure. This question is the main topic of this study and is supported by a series of real-scale experiments involving open-door electrical cabinets burning firstly under a calorimetric hood and then inside a mechanically-ventilated compartment. The facility and the fire tests are described in detail, and the main results are discussed. A model for describing a complex fire source (see Paragraph 4) is developed, applied for open-door electrical cabinet fires and used to perform calculations with SYLVIA code for fire scenarios carried out in confined/ventilated compartments. This paper complements the paper published previously (Plumecocq et al., 2011) on the characterisation of closed-door electrical cabinet fires in compartments. 2. Literature review

• the nature itself of each plastic material (it could be composed of different polymers that may include additives such as halogen or free-halogen flame retardant and whose composition may be uncertain), • the spatial distribution of materials inside the electrical cabinet, as seen in Fig. 3, which varies from one electrical cabinet to another. Characterising the combustion of electrical cabinets under a calorimetric hood has, however, been attempted, in order to cope with this problem (Mangs et al., 2003) and to provide useful input data (mass loss rates, heat release rates, chemical reactions, soot production, etc.) needed to simulate fire scenarios properly for computer modelling. Since the issue of fire simulation in a compartment in which atmosphere air vitiation due to combustion products from fire is very often found (Le Saux et al., 2008; Melis and Audouin, 2008; Peatross and Beyler, 1997), a second difficulty arises when taking into account the influence of oxygen depletion on the electrical cabinet combustion. For that purpose, the Heat Release Rate (HRR) measured under a calorimetric hood can then be used directly as an input value in the calculation methods, but additional modelling

The investigation of electrical or electronic cabinet fires has been scarce up to now and has been concerned exclusively with the nuclear industry. Most of the experimental data was published in internal reports (Chavez, 1987, 1988; Mangs and Keski-Rahkonen,

Fig. 2. Components where the fire occurred (Werner et al., 2009).

106

M. Coutin et al. / Nuclear Engineering and Design 286 (2015) 104–115

Recently, IRSN (Plumecocq et al., 2011) conducted experiments on closed-door electrical cabinets burning under a calorimetric hood and inside a mechanically-ventilated compartment. An analytical approach was used to investigate the effects of materials (PMMA, mixtures of polymers), of cabinet vents (sizes and locations), steel walls of the cabinet and oxygen depletion inside a cabinet on the HRR. This programme aimed at providing a response to safety concerns regarding the consequences of an electrical cabinet fire in a nuclear facility. Moreover, it also supplied an experimental database (in particular the HRR), in order to provide input data for fire codes and to assess fire scenarios concerning nuclear facilities and involving electrical cabinets as a fire source. 3. Characterisation of electrical cabinet fires

Fig. 3. Picture of an electrical cabinet used as a fire source.

1994, 1996). However, this topic is likely to be of wider interest for many engineering applications. The first experiments were carried out in the United States during the 1980s, at SANDIA National Laboratories (Chavez, 1987, 1988) using various cabinet geometries, ventilation openings and ignition conditions. The fire load within the cabinet consisted of cables either passing the IEEE-383 fire qualification test or not. The conclusions of this experimental programme showed the fire hazard posed by such electrical materials with a HRR peak of up to 175 kW for closed-door cabinets and 955 kW for open-door cabinets. Even though the fire propagation to adjacent cabinets was judged to be unlikely (Chavez, 1987), it was demonstrated that full involvement of the fire load within the cabinet could always be reached, depending on the ignition conditions. The influence of the closed-door electrical cabinet fires on the enclosure environment was also investigated in a 1400 m3 enclosure and revealed a large amount of smoke release, along with a limited gas temperature increase up to 100 ◦ C under the ceiling. Calorimetric experiments were conducted by VTT during the 1990s (Mangs et al., 2003; Mangs and Keski-Rahkonen, 1994, 1996) using electrical and electronic components as fire load within closed-door cabinets. The maximum HRR were measured in the 100–400 kW range. The influences of the cabinet size and the surface of the vents were investigated. The size of the openings was shown to be of prime importance for the fire growth and consequently for HRR. Assuming that the ventilation within the cabinet is driven by buoyancy and that the fire is ventilation-controlled, Mangs and Keski-Rahkonen (1994) developed a simple correlation giving the maximum HRR released by the cabinet. Avidor et al. (2003) from the University of Maryland have reported experimental simulations of a cabinet fire (about 40 tests), based on propane and heptane combustibles as a fire load. With the purpose of generating data to be used for the validation of an analytical model, this study has provided measurements of the thermal conditions inside a cabinet as a function of changing vent openings, fire sizes and fire locations. Considering the cabinet as a perfectly stirred reactor surrounded by a thermally thin steel wall, they were able to calculate the oxygen consumption and temperature within the cabinet using a one-zone model.

Nine experiments were performed in the frame of the PICSEL research programme carried out by IRSN in collaboration with AREVA NC, to characterise fires in electrical cabinets with open doors. The first two tests consisted in determining the behaviour of an electrical cabinet fire in a free atmosphere. This fire source was then implemented in a confined and mechanically ventilated multi-room to perform the next four tests. These tests aimed at understanding and quantifying the behaviour of the fire under different situations such as the impact on the fire room condition (confined situation, ventilation network, adjacent compartments and fire barrier). The three last tests were aimed at studying the effect of fire barriers on the development of the electrical cabinet fire in a confined and ventilated environment. 3.1. Description of fire tests 3.1.1. Electrical cabinet fire source The electrical cabinet used as a fire source in the experiments was an electro-technical cabinet with two modules. Both doors were left open to consider the most critical fire scenario, i.e., the highest possible heat release rate during the electrical cabinet fire. The electrical cabinet with steel walls measured 1.2 m × 0.6 m × 2 m (width × depth × height). The main electrical components were transformers, circuit breakers, trunking, cables, relays, terminal blocks, switches and contactors. The locations of the various components are shown in Fig. 3. The total fuel load was estimated at 44 kg and consisted of approximately 32% polyethylene vinyl acetate, 30% polyvinyl chloride, 26% polyamide, 9% polyethylene and 3% other compounds. Because the ignition due to hot shorts was not the purpose in this study, the electrical cabinet was not electrically powered (see Section 3.1.5 for the ignition of electrical cabinet fire source). 3.1.2. Saturne and DIVA facilities Two IRSN facilities were used, since the electrical cabinet fire is characterised both in a free atmosphere and in a confined environment. For the two fire experiments performed in a free atmosphere, the electrical cabinet was located in a large well-ventilated enclosure, SATURNE, which was designed as a large-scale calorimeter. Above the electrical cabinet, a 3 m diameter hood collected all of the combustion products (gas, soot) for filtering and analysis (see Fig. 4). For the seven tests performed in a confined and mechanically ventilated environment, fire tests were conducted in the multi-room large-scale fire test facility, DIVA. This test facility (shown in Fig. 5) consists of five rooms: 3 rooms of identical size (6 m × 5 m × 4 m) arranged in a row (referred to as Rooms 1, 2 and 3) and a corridor of 156 m3 (15.6 m × 2.5 m × 4 m) in volume (Room 0). Moreover, an upper room of 176 m3 (8.8 m × 5 m × 4 m) in volume (Room 4) is located above Room 3 and part of the adjacent

M. Coutin et al. / Nuclear Engineering and Design 286 (2015) 104–115

107

Fig. 4. Pictures of the SATURNE facility.

corridor. Nevertheless, Room 4 was not used for this study. The various rooms can be connected via doors, simple openings and calibrated leak passages (to simulate leaks through an actual closed door and/or through a transfer grid between two rooms). They can also be connected with a ventilation network, with one inlet duct and one exhaust duct per compartment. The ventilation system of the DIVA test facility consists of two separate circuits (one for inlet and one for outlet), each equipped with fans. 3.1.3. Configurations of fire tests In the SATURNE facility, the electrical cabinet was located under the large-scale calorimeter, as shown in Fig. 4. The experimental procedure consisted in igniting the electrical cabinet using a gas burner located at its base (see Section 3.1.5) and to record the evolution of the fire by means of 157 sensors (temperature, gas analysers, weighting system, etc.). Some main measurements are described in more detail in (Coutin, 2007). Two tests, named PXA3 and PXA3b, were performed, the second test for reproducibility. In the DIVA facility, the initial study configuration, which is similar for the seven tests performed during the experimental programme, is shown in Fig. 6 and described below. The four rooms were linked together through the ventilation network and by two circular calibrated leaks of 62 mm in diameter between Rooms 0 and 2, and Rooms 0 and 3. A larger circular calibrated leak of 68 mm

Fig. 5. Schematic drawing of the DIVA facility.

in diameter was used between Rooms 0 and 1. The same ventilation regime before fire ignition was applied for all fire scenarios in the DIVA facility. Indeed, the inlet renewal rates were of 2 h−1 for the four rooms and the outlet renewal rates were of 2.5 h−1 for Rooms 1, 2 and 3, and 0.8 h−1 for Room 0 (see corresponding flow rates in Table 1). This means that an air flow rate of 60 m3 h−1 was supplied to Rooms 1 to 3 from the corridor (Room 0). The initial relative pressures were −80 Pa in Room 0, −100 Pa in Room 1 and −120 Pa in Rooms 2 and 3. These pressure values respect a pressure loss cascade, as usually required in Nuclear Reprocessing Plants (NRP). The inlet branches were located in the upper part of all four rooms and the opening sides were directed towards the west walls for Rooms 1, 2 and 3, and towards the north wall for Room 0. The outlet branches were positioned in the upper part for Rooms 0 and 1, in the upper or lower part for Room 2 and in the lower part for Room 3. The opening sides of the outlet branch were directed towards the east walls for Rooms 1, 2 and 3, and towards the north wall for Room 0. The ventilation system of the four rooms was maintained throughout all of the fire tests. In order to prevent concrete failure due to the thermal stress from fire, the ceiling, the four side walls (only 1.2 m below the ceiling) and the west wall (in its centre on 2.6 m wide and over the entire height of the fire room) were insulated with 5 cm thick Rockwool panels (THERMIPAN® ). These

Fig. 6. Initial configuration of the DIVA facility with ventilation regime common to the fire tests performed in a confined environment.

108

M. Coutin et al. / Nuclear Engineering and Design 286 (2015) 104–115

Table 1 Initial pressure and renewal rate in the rooms before fire ignition and branch location in the rooms of the DIVA facility. Room

Room 0 Room 1 Room 2 Room 3

Nominal pressure (Pa)

−80 −100 −120 −120

Nominal renewal rate (h−1 )

Branch location

Inlet

Outlet

Inlet

Outlet

2 (300 m3 h−1 ) 2 (240 m3 h−1 ) 2 (240 m3 h−1 ) 2 (240 m3 h−1 )

0.8 (120 m3 h−1 ) 2.5 (300 m3 h−1 ) 2.5 (300 m3 h−1 ) 2.5 (300 m3 h−1 )

Upper part Upper part Upper part Upper part

Upper part Upper part Upper or lower part Lower part

panels were attached to metallic frames screwed directly onto the concrete. The electrical cabinet was located at 10 cm from the west wall of Room 2, in its centre, and the cabinet opening was directed towards the east wall of the room. For each of the seven tests performed in the DIVA facility, the number of sensors varied from 647 to 733. Some of these measurements, together with the uncertainties of the sensors, are described in more detail in (Coutin et al., 2012). Among these, the cabinet side wall temperature, the mass loss rate of the cabinet, the volume flow rate through the ducts and leaks, the pressure in the fire room, the heat flux through the walls of the fire room and the gas temperature in the fire room are shown in (Coutin et al., 2012) for the PXV1 test. 3.1.4. Description of fire scenarios The features of the seven tests performed in the DIVA facility are summarised in Table 2 and are described below. In this study, only one parameter is considered to change (except for the reproducibility test) from the previous fire test to the next fire test. 3.1.4.1. PXR3 test. Indeed, the scenario of the first test, PXR3, was the common configuration described previously (see Fig. 6), with the outlet branch located in the lower part of the fire room. 3.1.4.2. PXR3b test. The reproducibility of the PXR3 fire test was investigated during the PXR3b test, so the experimental configurations were identical for both tests.

the ignition of a propane burner, see Section 3.1.5). Except for this fire damper, the experimental configuration of the PXS1 test was the same as that for the PXS0 test. 3.1.4.7. PXS2 test. Compared to the PXS1 test, an additional fire damper was placed in the outlet branch of the fire room for the last test, PXS2. As previously, the objective of this test was to investigate the effect on fire development of a fire damper closure (ALDES VRFI 2.15) located in the ventilation inlet and outlet of the fire room. For the PXS2 test, the fire damper located in the inlet was shut down at 3 min after the beginning of the fire (as for the PXS1 test), whereas the damper placed in the outlet was shut down about 8 min after the fire beginning, because the fire was fully developed inside the cabinet. 3.1.5. Experimental procedure For tests performed in the DIVA multi-room facility, an underpressure cascade is performed prior to fire ignition, according to the initial conditions, as defined in Fig. 6. The ignition of the electrical cabinet was remotely activated. A linear propane burner ignited the fuel load at the base of the cabinet, along its entire width. The average heat release rate generated by the gas burner was 9 kW and the burner was switched off after 3 min. After that, the fire was allowed to develop freely until selfextinction. The inlet and outlet fans of the ventilation network were maintained throughout the duration of the test. 3.2. Main results and discussion

3.1.4.3. PXV1 test. The third test, PXV1, was performed with the objective of studying the influence of the outlet branch location in the fire room on the fire growth. The configuration of this fire test was the same as that for PXR3b test, but with the outlet branch placed in the upper part of the fire room. 3.1.4.4. PXV2 test. The objective of the fourth test, named PXV2, was to study the influence of changing the ventilation regime during the test. For this test, the configuration was similar to that of the PXV1 test, except that the ventilation flow rates were reduced by half at 20 min after the ignition of the fire source, this duration of 20 min being representative of an average time to modify ventilation regime in case of true fire in nuclear facilities. 3.1.4.5. PXS0 test. The next test, PXS0, proposed a new fire scenario consisting in replacing the calibrated leak between Rooms 2 and 3 by a fire door, as a fire barrier. The objective was to study the impact of the presence of a fire door on fire development. The fire door used for this test was an SMSL type door with the following technical features: single leaf, metal door, unit without vision panel, 2 h fire rating, 2.04 m height, 0.93 m width, direction of opening from Room 2 to Room 3. 3.1.4.6. PXS1 test. The objective of the sixth test, PXS1, was to study the influence on fire development following a closure of a fire damper located in the inlet of the fire room. An ALDES VRFI 2.15 fire damper was thus placed in the inlet of Room 2 and was shut down just 3 min after the start of the fire (starting corresponds to

3.2.1. Characteristic stages of the cabinet fire development The electrical cabinet fire source is characterised by the evolution of the heat release rate, which expresses the quantity of heat released by the combustion process per unit time. As previously emphasised by Babrauskas and Peacock (1992), the heat release rate is the main parameter for assessing and understanding the consequences of a fire. Different methods can be used to determine the heat release rate: the “mechanical” method (Babrauskas and Grayson, 1996), based on the measure of mass loss rate, the “chemical” method (Babrauskas and Grayson, 1996; Coutin, 2007), based mainly on the measure of oxygen consumption by the fire source, or the “thermal” method (Hamins et al., 2008; Coutin et al., 2012) based on the thermal balance inside the fire compartment. In the free atmosphere, the heat release rate of the electrical cabinet fire was obtained by the “chemical” method (Coutin, 2007), whereas in the confined environment the “thermal” method was found to be the most adequate method to determine the heat release rate of the electrical cabinet fire (Coutin et al., 2012). The combustion of the electrical cabinet follows a typical evolution of the heat release rate of the fire, composed of three successive stages: an incubation stage, a fast spreading stage and a decay stage until the extinction of the fire. 3.2.1.1. Incubation stage. The incubation stage corresponds to the propagation of the flame along the fuel and to the heating of the cabinet walls. The duration of this stage varies between 6 and 12 min for all tests performed in a free atmosphere or in a confined and

M. Coutin et al. / Nuclear Engineering and Design 286 (2015) 104–115

109

Table 2 Parameters of the seven tests performed in the multi-room DIVA facility. Test name

PXR3 PXR3b PXV1 PXV2 PXS0 PXS1 PXS2

Room 2

Transfer between Rooms 2 and 3

Fan operation

Inlet

Outlet

Damper

Damper

Branch location

Calibrated leak

Fire door

No No No No No Yes Yes

No No No No No No Yes

Lower part Lower part Upper part Upper part Upper part Upper part Upper part

Yes Yes Yes Yes No No No

No No No No Yes Yes Yes

No No No Yes No No No

Table 3 Instantaneous heat release rates and global magnitude of the fire. Test name

dfire (min)

 fuel mass loss (%)

Q˙ end incub (kW)

Q˙ max (kW)

D(MJ)

Hc (MJ kg

PXA3 PXA3b PXR3 PXR3b PXV1 PXV2 PXS0 PXS1 PXS2

120 132 97 72 99 75 97 90 50

100 99 61 45 49 40 44 42 38

110 101 90 72 85 61 87 69 48

1636 1174 951 539 594 610 400 500 680

1206 1115 379 247 266 220 221 265 202

27.4 25.3 14.1 12.6 12.3 12.4 11.4 14.2 12.1

3.2.1.2. Fast spreading stage. During the fast spreading stage, the fire growth rate increases very fast and the flame spreads quickly over all of the materials available inside the cabinet. The duration and the levels of the heat release rate depend essentially on the oxygen concentration near the fire. This fast spreading stage lasts approximately 4 times longer for fires in a free atmosphere (PXA3 and PXA3b) than for those performed in a confined compartment under the experimental conditions of the PICSEL tests (see Table 4). Lengthening the duration of this stage in a free atmosphere induces fuel consumption about three times higher than in enclosure. Except for the PXR3 test, the duration and the mass of fuel consumed during the fast spread stage are equivalent, respectively of about 10 min and 30% (see Table 4) for all of the tests performed in a confined environment. This result highlights that fire growth mainly depends on the initial amount of oxygen available for the combustion. This also shows that the fire growth is slightly affected by the modification of the ventilation conditions performed between the tests (location of the outlet branch, presence of fire barrier devices), or during the tests (ventilation operation, shutdown of fire barrier devices). For the PXR3 test, the flame propagates differently in the cabinet, involving some accumulation of pyrolysis gases (excess pyrolysate (Pagni and Shih, 1977) not burned in the flame) under the ceiling of the fire room. The combustion of flammable gases generates a peak in the heat release rate of about 950 kW for the PXR3 test (see Fig. 8), much higher than the maximum heat release rates ranging from 400 to 700 kW observed during the other tests performed in the DIVA facility (see Table 3). This additional combustion of excess pyrolysate induces a faster consumption of the oxygen available in the fire room (see Fig. 9). Consequently, the duration of the fast spread

)

stage for the PXR3 test is about 30% shorter in comparison with the other tests performed in a confined compartment.

3.2.1.3. Decay stage. The decay stage of the combustion corresponds to the falling of a significant part of the fuel load down onto the floor of the cabinet. Thus, the pyrolysis of the fuel is reduced substantially, due to the reduction of the exchange area between the fuel and the hot gases. In a confined environment, the durations of this decay stage, as well as the mass of the consumed fuel, are very different from one test to the next, respectively from 34 to 82 min and from 5% to 29% (see Table 4). During this stage, this variability in regard to the fire results comes from two opposite effects: • the oxygen concentration increasing in the fire room, due to the inflow of fresh air by the ventilation, which can keep the fire burning thus avoiding fire extinction, • the decrease in the fuel pyrolysis, due to the cooling of the fuel, which is favourable to the fire extinction.

2 x10 1.0

0.9 0.8

PXA3

0.7

MLR (g s-1)

mechanically ventilated compartment (see Table 4). This duration is strongly dependent on the fire propagation along the electrical components at the beginning of the fire. Furthermore, the flame spread is also strongly influenced by the fall of burning electrical components. Despite the random character of the flame propagation, the mass of fuel consumed during this stage remains of the same order of magnitude and less than 5%. The acceleration of the combustion at the end of the incubation stage takes place for heat release rates of about 100 kW (see Table 3).

−1

PXA3b

0.6 0.5 0.4 0.3 0.2 0.1 0.0 0.0

0.5

1.0

1.5

2.0 Time (s)

2.5

3.0

3.5 x10

Fig. 7. Time evolution of the mass loss rate for the PXA3 and PXA3b tests.

3

110

M. Coutin et al. / Nuclear Engineering and Design 286 (2015) 104–115

Table 4 Duration and fuel mass loss for each fire stage. Test name

 fuel mass loss (%)

dfire (min)

PXA3 PXA3b PXR3 PXR3b PXV1 PXV2 PXS0 PXS1 PXS2

Incubation stage

Fast spread stage

Decay stage

Incubation stage

Fast spread stage

Decay stage

9 10 8 9 10 8 12 9 6

45 37 7 11 11 12 10 10 9

66 85 82 52 78 56 75 71 34

5 5 4 3 3 2 5 4 2

88 87 28 31 30 31 30 31 31

7 7 29 11 16 7 9 7 5

During this stage, the HRR is less than 100 kW in both the free and confined environments, as illustrated in Fig. 8 for the PXR3 and PXR3b fire tests and in Fig. 11 for the PXV1 fire test. Nevertheless, a low HRR peak of 250 kW was observed for the PXR3 test (see Fig. 8). At the end of cabinet fire, fire extinction occurs in a free atmosphere due to the lack of fuel while, in a confined environment, it is often due to oxygen depletion inside the fire room and due to the cooling of the fuel. Indeed, the mass of burned fuel at the end of the fire is only between 38% and 61% of the initial combustible mass (see Table 3). 3.2.2. Reproducibility of electrical cabinet fires In a free atmosphere, flame propagation along the electrical components takes place differently between the PXA3 and PXA3b fire tests. This difference in flame spread is due to the fall of a tray filled with electrical components, as observed in the PXA3b test, during the incubation stage. This fall is not observed during the PXA3 test. This movement of electrical components down to the cabinet involves a wide space between the upper and lower combustible materials in the right module of the cabinet and, consequently, stops the fire propagation on this cabinet side. The flame propagates at first from the left module of the cabinet then spreads laterally towards the right module. Because of this specific flame spread throughout both modules of the cabinet, the strong intensity and short-duration phase of the HRR obtained during the PXA3 test (1.6 MW for 2 min, see Fig. 7) is replaced by a phase of lesser intensity but longer duration of the HRR for the PXA3b test (1.2 MW for 7 min, see Fig. 7). Nevertheless, the PXA3 and PXA3b tests show similar fire duration of about 2 h (see Table 3). The time integration of physical quantities (HRR, YCO2 , YCO , Ysoot ) during the fire duration is also comparable for both tests, with in particular: • a quasi-complete combustion of fuel,

• an effective combustion heat between 25.3 and 27.4 MJ kg−1 , • mean production rates (defined as the combustion product mass to pyrolysed fuel mass ratio) of CO, CO2 and soot of 12.4 ± 0.7%, 174.7 ± 1.8% and 1.7 ± 0.2% respectively. These global quantities are equivalent, despite the difference in the flame propagation observed during the PXA3 and PXA3b tests. The propagation of the flame along the electrical components during the incubation stage is strongly influenced by the falling of electrical materials down into the cabinet. These stochastic events modify the development of the fire, which makes a large variability for electrical cabinet fires in terms of instantaneous physical quantities. Nevertheless, at the same time, the quantities integrated for the fire duration, for the electrical cabinet in a free atmosphere (PXA3 and PXA3b) are, on the other hand, reproducible (see Table 3, fuel mass loss and total energy release). In a ventilated confined environment, the behaviour of the cabinet fire shows satisfactory similarities from one test to the next, during all fire tests (see Table 3 and Table 4), like the heat release rate at the end of the incubation stage, the partial combustion of the available fuel, the fire duration during the fast spreading stage, the lower effective heat of combustion of about 50% compared to that in the free atmosphere (see also Coutin et al., 2012). Following the example of a cabinet fire in a free open atmosphere, the complex and random nature of the flame propagation on the elements of the cabinet can create an important statistical dispersion in terms of reproducibility (see Fig. 8, the HRR time evolution, Fig. 8 of PXR3 and PXR3b tests) in a ventilated confined environment. 3.2.3. Effect of the confinement Due to a low air renewal rate during the tests performed in the DIVA facility, the fire growth in a confined environment mainly

22 3 x10 1.0

20

0.9

18

0.8

PXR3 16

PXR3b

X_O2 (%)

HRR (kW )

0.7 0.6 0.5

14

12

PXR3

0.4

0.2

8

0.1

6 0.0

0.0 0.0

PXR3b

10

0.3

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Time (s)

4.5

5.0

5.5

6.0

6.5

7.0 x10

Fig. 8. Time evolution of the heat release rate for the PXR3 and PXR3b tests.

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Time (s)

4.0

4.5

5.0

5.5

6.0

6.5

7.0 x10

3

3

Fig. 9. Time evolution of the volume fraction of oxygen in the upper part of the fire room for the PXR3 and PXR3b tests.

M. Coutin et al. / Nuclear Engineering and Design 286 (2015) 104–115

depends on the initial amount of oxygen inside the room. When comparing the fire tests (see Table 3) performed in free and confined atmospheres, the oxygen depletion lead to a significant reduction in the fire duration (up to about 60%), in the maximum heat release rate (up to about 75%), in the combustion heat (up to about 60%) and in the radiative heat transfer in front of the cabinet, due to low HRR and smoke attenuation. 3.2.4. Effect of the outlet branch location Gas extraction in the upper part of the fire room promotes the evacuation of smoke accumulated under the ceiling, favours room oxygenation. Consequently, the fire duration increases about 37% (see PXV1 versus PXR3b in Table 3) compared to the case where the extraction is located in the lower part of the room. The extraction in the upper part also reduces the vitiation of the gaseous atmosphere in the lower part of the room and leads to a lower attenuation by soot of the radiation emitted directly by the fire source. But, no significant effect of the location of the fire room extraction (see Fig. 12) is observed on the maximum heat release rate of the fire, on the maximum pressure peak and on the maximal mean temperature of the gases in the fire room, or even on the production of smoke and its transfer towards the neighbouring rooms. 3.2.5. Effect of the ventilation operation The change in the ventilation half-regime 20 min after the ignition of the electrical cabinet has no effect on the heat release rate of the fire, the pressure and the temperature of gases in the fire room, because these maximal values are reached before the change of the ventilation flow rate. Also, the ventilation half-regime transition has no significant influence on the production and transfer of smoke to the neighbouring rooms under the experimental conditions of the PICSEL tests. The ventilation half-regime transition, performed at the beginning of the fire decay stage, leads to a decrease in the room oxygenation kinetics, which shortens the fire duration. Moreover, it increases the gaseous atmosphere vitiation by smoke involving a significant decrease of radiative heat transfer from the flames in front of the cabinet. 3.2.6. Effect of the fire barrier Tests implementing a fire door and fire dampers show that the fire modifies the airflow behaviour of both fire barrier devices by increasing the airflow resistances of the door and the fire dampers. The consequence of this increase in airflow resistance is in particular a significant reduced transfer of smoke through the leaks of the fire door, at the end of the fast spreading stage. The airflow resistance of the fire dampers is also observed to depend on the direction of the airflow. Although the fire barrier tests lead to heat release rate peaks of various intensities, the fire barrier elements do not have a significant influence on the heat release rate of the fire. The various heat release rate peaks during fire tests are mainly attributed to variations in propagation of the flame over the fuel and to the falling of electrical materials. When closing the admission and maintaining the extraction of gases of the fire room (PXS1 test), the ventilation creates a breath of air, having as consequence an increase in the rates of leaks entering the fire room. According to the position of the leaks, their airflow resistance and the level of ventilation in the extraction, a new and limited heat release rate increase of the fire can take place during the test (random phenomenon), which impacts the fire duration. So, a new increase in the fire heat release rate occurred during the PXS1 test, but was less significant (of the order of 50 kW). This leads to an increase in the pressure in the room, which quickly limits the inflow of oxygen through the leaks in the fire room. Of course, the closure

111

of the damper at the extraction leads to a reduction in the fire heat release rate, since oxygen transfer to the fire room is stopped. The closure of the fire dampers involves an increase in the pressure in the room. However, this increase is limited due to the significant leak rate of the fire door. The tightness of this door was reached only at the end of the spreading stage. The fire damper closure also has weak influence on the average temperature of the gases in the fire room, because the heat is mainly transferred to the walls of the room. The growth of the fire is little affected when closing the admission and maintaining the extraction of gases from the fire room (PXS1 test). On the other hand, the closure of the fire damper at the extraction (PXS2 test) enhances the smoke transfer towards the neighbouring rooms through leaks, because of the increase in the pressure in the fire room. 4. Open-door electrical cabinet fire modelling As discussed previously, the combustion of an electrical cabinet is a very complex issue, even more so when it burns under well-confined and low ventilated conditions involving vitiated atmosphere. Fuel characteristics are not perfectly known and may vary over time, depending on the fire spread over the various materials inside the cabinet. Current knowledge of this type of fire source does not allow an accurate mode of the fire growth to be developed, all the more since some of these were observed to be weakly reproducible. Therefore, the developed modelling approach for this complex fire type was kept robust and simplifying, i.e., using the mass loss rate of the fuel under well ventilated conditions as an input of the model and some additional assumptions discussed hereafter. Finally, the fire source is characterised by its MLR, its HRR and a combustion reaction. 4.1. Heat release rate The heat release rate of a burning open-door electrical cabinet can be defined as: ˙ ∞ (XO2 )Hc Q˙ = m

(1)

Fuel characteristics are complex, due to the diversity of materials and their locations inside the cabinet. From this proposed modelling, the fuel is assumed to be homogeneous and average properties over the fire duration are used in the model. By considering an average value for the effective heat of combustion (see Table 3 for Hc experimentally determined), it is assumed that combustible materials participate in the combustion at a constant ratio, although fuel properties vary over time. The mass loss rate ˙ ∞ , is determined experimenunder well ventilated conditions, m tally. This parameter is estimated from the combustion of the electrical cabinet under a large-scale calorimeter (Coutin, 2007), as carried out in this study (PXA3 and PXA3b, see Sections 3.2.1 and 3.2.2). One difficulty in assessing the mass loss rate is linked to weakly reproducibility phenomena, as shown in Fig. 7 for two similar tests of the PICSEL programme, performed under a calorimetric hood. Indeed, for this type of fuel, the pyrolysis surface changes over time, depending on the fire spread over the components inside the cabinet, as well as the falling of materials to the bottom of the cabinet during the fast spreading stage of the fire, due to their vertical arrangement within the cabinet. For simulating the PICSEL experiments, the mass loss rate of the PXA3 fire test (see Fig. 7) has been used as input in the SYLVIA fire modelling (Audouin et al., 2011), because the HRR peak was found to be higher than in the PXA3b experiment, assuming likely higher fire consequences in compartments. Fires in confined and ventilated compartments, like in the PICSEL fire tests, often lead to a significant decrease in the mass loss

112

M. Coutin et al. / Nuclear Engineering and Design 286 (2015) 104–115 2 x10 6

1.0 0.9

Peatross and Beyler law (1997) 5

HTP high inlet

0.8

PXV1 Experiment

TBP/HTP low inlet

0.6

HTP low inlet

PXV1 Model

4

HRR (kW )

Dimensionless MLR (-)

Oil high inlet 0.7

0.5

3

0.4 2

0.3 1

0.2 0.1

0

0.0 10

11

12

13

14

15

16

17

18

19

20

21

22

0.0

0.5

Fig. 10. Evolution of the steady-state fuel mass loss rate with oxygen (Melis and Audouin, 2008).

rate (and thus in the HRR) compared to the one obtained in a free atmosphere. This decrease is mainly due to oxygen depletion in the fire room, because the air renewal rate can be quite low compared to the fire power (Melis and Audouin, 2008). In order to take into account this phenomenon, a limiting-oxygen law, (XO2 ), is applied to the mass loss rate of the fuel, as shown in Eq. (1). PICSEL experiment simulations have been performed using the oxygen-limiting correlation proposed by Peatross and Beyler (1997). This correlation is a linear function of the mass loss rate of the fuel according to the oxygen volume fraction available for combustion close to the combustible (see Fig. 10 from Melis and Audouin (2008)). The PICSEL experiments showed that up to 30% of the HRR is retained inside the cabinet by the pyrolysis of the fuel, and by the walls of the cabinet (Coutin et al., 2012). These phenomena are explicitly taken into account in the fire source model. The external walls of the cabinet are consequently modelled and these ones thermally exchange with the surrounding gases (inside and outside the cabinet), by convective and radiative heat transfers. 4.2. Combustion reaction Chemical reactions occurring during the burning of an electrical cabinet are complex, due to the diversity of materials inside the cabinet. Current knowledge on the combustion of such a fire source does not allow detailed chemical reactions to be taken into account. Thus, a simplified chemical reaction (one step, irreversible) expressed in terms of mass is used as: 1 kg of fuel + O2 O2 → CO2 CO2 + CO CO + H2 O H2 O + C C

(2)

In Eq. (2), it is assumed that the fuel is homogeneous and that chemical reactions occur simultaneously with the same kinetics, although they vary over time. This equation does not take into account the release of hydrocarbons, as well as other species, such as hydrogen chloride or hydrogen cyanide, in the absence of available experimental data. The values of the reaction coefficients averaged over the fire duration are used in this study, although these could change depending on the oxygen content in the fire room. Coefficients are deduced experimentally from the mass of chemical species and the pyrolysed mass of fuel (mass ratio). Oxygen consumption is given by: O2

Hc = HO2

1.0

1.5

2.0

2.5

Time (s)

O2 near flame base (%vol)

(3)

where HO2 is the heat released by the oxygen consumption, set to 13.1 MJ kg−1 (Huggett, 1980).

3.0

3.5

4.0 x10

3

Fig. 11. Comparison model/experiment of the HRR time evolution for the PXV1 test.

Since the amount of water vapour was not evaluated experimentally, the water vapour coefficient is determined by the mass balance of the chemical reaction. The fuel database of the SYLVIA code is provided with data obtained from well ventilated conditions. In order to use this data for the simulation of confined fires, a correction is applied to the combustion reaction coefficients, to account for a decrease in the efficiency of the reaction with the decrease of oxygen, resulting in an increase in the amount of unburned gases. A correction factor, ˇ, is then introduced to account for the efficiency of the reaction: ˇ=

Hc Hc∞

(4)

where Hc∞ is the effective combustion heat of the cabinet under well ventilated conditions. A mean value of 18 MJ kg−1 (from the PICSEL A fire tests) was obtained during the fast spreading stage of the cabinet observed under calorimeter. Thus, Eq. (4) is used in Eq. (3) for the assessment of the oxygen consumption under a confined atmosphere. For combustion products, the following relations, based on the PICSEL results, are used in a first approximation: CO2 = ˇCO2 ∞

(5)

CO = 2CO∞

(6)

C = 2C∞

(7)

No matter which PICSEL test was performed, the effect of the air vitiation remains nearly the same in terms of the production of carbon monoxide and soot species. These species are mainly produced during the decay stage of the cabinet fire, when materials are relocated in the lower part of the cabinet. Consequently, in order to take into account this air vitiation effect (see Eqs. (6) and (7)), two times the values of CO and soot obtained from a cabinet fire test in a free atmosphere, as measured during the fire tests in DIVA compartments, are assumed. A typical value for ˇ is 0.67 for the combustion of an electrical cabinet in a 120 m3 fire room, with a low air renewal rate. Nevertheless, due to the combustion of excess pyrolysate observed in the PXR3 test (see Section 3.2.1), the simulation consists in this case of using a combustion reaction efficiency of 0.8. 4.3. Model application to the PICSEL experiments The model was implemented in the SYLVIA code (Audouin et al., 2011), developed by IRSN for the simulation of phenomena dealing with ventilation networks, fires in a confined atmosphere and transport of contamination within nuclear plants. This fire code

M. Coutin et al. / Nuclear Engineering and Design 286 (2015) 104–115

113

Fig. 12. Comparison of the simulation results against experiments: (a) maximum MLR, (b) maximum HRR, (c) maximum pressure in the fire room, (d) maximum value of the mean gas temperature in the fire room, (e) minimum value of the mean oxygen concentration in the fire room, (f) maximum value of the mean carbon dioxide concentration in the fire room.

adopts a zone type approach. The fire room is divided into two zones: the lower zone modelling fresh gases and the upper zone modelling the combustion gases, as well as fresh gases dragged by plume. The plume supplies the upper zone with gases, whose volume increases, leading to a lowering of the gas interface between the two zones.

The model was applied to the PICSEL experiments involving open-door electrical cabinets burning inside a mechanicallyventilated compartment. The comparison of the predicted time evolution of the HRR with experimental data is reported in Fig. 11 for the PXV1 test and deviations from the experimental data of a few predicted quantities are reported in Fig. 12 for all of the tests.

114

M. Coutin et al. / Nuclear Engineering and Design 286 (2015) 104–115

The PICSEL experiments led to different durations of the incubation stage of the fire, because the fire spreading inside the cabinet is weakly reproducible. The use of a mass loss rate of the fuel under well ventilated conditions as an input for the model enforces the scenario of the flame propagation over the fuel obtained in an open atmosphere, as well as the relocation of materials inside the cabinet. This choice of input leads to an underestimation of the fire stage duration by nearly 30% for the PXV1 test, as shown in Fig. 11. Differences concerning the durations of the incubation stage are also observed for other tests, in the range of 5% for PXS2 and 40% for PXS0. Also observed in Figs. 11 and 12b is the maximum value of the predicted HRR, which is lower than the experimental one. In addition to uncertainties linked to non-reproducible phenomena, another difficulty in the prediction of the HRR when using a zone code is linked to the estimation of the oxygen available for combustion, since no gas stratification is considered inside each control volume (use of averaged values). The Peatross and Beyler correlation is applied here to various solid fuels with vertical geometries. This correlation overestimates the oxygen available for combustion, as shown in Fig. 12e. Amazingly, the predicted mass loss rate of the fuel is underestimated for all of the PICSEL tests performed in a confined atmosphere (see Fig. 12a). This behaviour could be explained by thermal effects coming from hot gases and soot in the fire room, which would increase the pyrolysis of materials inside the cabinet. Another reason could be the validity of the Peatross and Beyler correlation, which works well for some liquid pool fires (Le Saux et al., 2008; Melis and Audouin, 2008), but could be unsatisfactory for such a complex solid fire source, Investigations are under progress at IRSN to find a more appropriate law for complex solid fire sources. Finally, the decreasing stage of the fire, resulting from the decrease in oxygen content in the fire room and from the reduced pyrolysis surface of the fuel, induced by relocated materials in the bottom of the cabinet, is satisfactorily assessed by the model (see Fig. 11 for PXV1). Though simulations were performed using a constant combustion reaction that does not allow the air vitiation effect on the production of species to be taken into account, the latter led to quite good predictions of the mean species concentrations in the fire room, as shown in Fig. 12f for carbon dioxide. The same trends were obtained for other species used in the combustion reaction defined by Eq. (2). At the beginning of a confined enclosure fire, an over-pressure peak is experienced in the fire room. This over-pressure is a potential mechanical threat to some ventilation devices, such as filters, dampers or fire doors. An over-pressure peak is one of the most difficult quantities to predict properly (see Fig. 12c), because it is very sensitive to both the characteristics of the ventilation network, the heat transfer to the walls and the fire source (Pretrel et al., 2012). Deviations from experimental data can be attributed to various parameters: modelling errors (for instance, error in the modelling of the ignition behaviour of the fire source), error in the predicted fuel mass loss rate, error in the heat exchange between gas and walls, and so on. For PICSEL experiments, the mean gas temperatures in the fire room are quite well calculated by the SYLVIA code (see Fig. 12d), although some discrepancies compared with experimental data are observed in the calculated heat release rates (see Fig. 12b).

5. Conclusion The properties of electrical cabinet fires obtained from a large-scale calorimeter were produced by a series of real-scale experiments involving open-door electrical cabinets burning both under a hood and inside a confined and mechanically-ventilated compartment. Whatever the fire scenario (including air renewal

rate, outlet branch location, ventilation management or fire barriers) for this study, the main results concerning the cabinet combustion showed three characteristic steps for HRR evolution: • An incubation stage with HRR increasing up to about 100 kW, with a duration ranging between 6 and 12 min and with a fuel mass loss of between 2% and 5% of initial mass of the combustible materials (i.e., less than 2.1 kg). • A fast fire propagation depending mainly on the initial oxygen content available in the fire room. Due to oxygen depletion in the fire room, the maximum HRR of the cabinet were of about 50%, compared with an open atmosphere. Furthermore, the fire durations were observed to be approximately 4 times longer and the fuel consumptions to be 3 times higher in a free atmosphere versus a confined environment. Finally, the durations and the mass ratio of the fuel consumed were almost constant, of about 10 min and 30% (i.e., 13 kg of the initial mass) respectively in a confined compartment. • A decay period up until fire extinction, in which the HRR measured were less than 100 kW, in both a free and a confined environment. For this last stage, the fire durations, as well as the mass of the consumed fuel obtained, during fire tests in the confined environment were very scattered, from 34 to 82 min and from 5% (i.e., 2.2 kg) and 29% (i.e., 13 kg) respectively. Moreover, the fire extinctions were often driven both by the oxygen depletion inside the fire room and by the cooling of the fuel. The average effective combustion heats ranged from 25.3 to 27.4 MJ kg−1 of fuel in a free atmosphere, while they were measured at between 11.4 and 14.1 MJ kg−1 in the case of a confined environment, that is, about 50% lower. A complex fire source model applied in this study for open-door electrical cabinet fires is then developed, based on the experimental data obtained under large-scale calorimeter. Up to now, accurate and detailed knowledge about each single material constituting this fire source does not allow a predictive fire cabinet model to be developed properly, due to the complex location of electrical components and the various types of materials (polyethylene, polyvinyl chloride, polyamide, etc.) constituting electrical components. Consequently, this complex fire source showed only an overall reproducibility (combustion heat, production rates of combustion gases, etc.) but a relatively weak reproducibility concerning the time evolution of mass loss rate (MLR) and the heat release rate (HRR) especially. Nevertheless, based on the usual practice concerning complex fire sources in fire safety engineering, the fire source fire properties are determined under a large-scale calorimeter in an open atmosphere. Then, with some additional assumptions discussed previously (see Section 4.1), the experimental MLR evolution (also combustion heat, chemical reaction, etc.) can be introduced as input parameters in the fire code to predict the consequences of a real cabinet fire scenario in compartments, which must be modelled taking into account the air vitiation. Thanks to this engineering approach, 7 fire scenarios consisting in a fire cabinet within confined and ventilated rooms were simulated by means of a two-zone fire code (SYLVIA). The major outcome of this study is that, both fire characterisation of cabinet in open atmosphere and modelling of oxygen depletion inside the fire room allow us to predict with rather good agreement the fire scenarios performed in this study (in the worst case, the order of magnitude is still preserved). More generally, for any electrical cabinet available in NRP or NPP facilities, it will be necessary to determine its fire properties (heat release rate, chemical species, etc.) under large scale calorimeter. Nevertheless, some issue concerning the validity of the Peatross and Beyler correlation for such a fire source (i.e., an

M. Coutin et al. / Nuclear Engineering and Design 286 (2015) 104–115

electrical cabinet and, more widely, the complex fire sources) will need further investigations. Acknowledgement This work was performed within the framework of the PICSEL experimental programme, a joint research programme carried out by IRSN with the support of AREVA NC. References Audouin, L., Chandra, L., Consalvi, J.-L., Gay, L., Gorza, E., Hohm, V., Hostikka, S., Ito, T., Klein-Hessling, W., Lallemand, C., Magnusson, T., Noterman, N., Park, J.S., Peco, J., Rigollet, L., Suard, S., Van-Hees, P., 2011. Quantifying differences between computational results and measurements in the case of a large-scale well-confined fire scenario. Nucl. Eng. Des. 241, 18–31. Avidor, E., Joglar-Billoch, F.J., Mowrer, F.W., Modarres, M., 2003. Hazard assessment of fire in electrical cabinets. Nucl. Technol. 144, 337–357. Babrauskas, V., Grayson, S.J., 1996. Heat Release Rate in Fires. Chapman & Hall Ed, ISBN-0-419-161007. Babrauskas, V., Peacock, R.D., 1992. Heat release rate: the single most important variable in fire hazard. Fire Saf. J. 18, 255–272. Chavez, J.M., 1987. An experimental investigation of internally ignited fires in nuclear power plant control cabinets, Part I: Cabinet effects tests. NUREG/CR4527, SAND86-0336, vol. 1. Sandia National Laboratories. Chavez, J.M., 1988. An experimental investigation of internally ignited fires in nuclear power plant control cabinets, Part II: Room effects tests. NUREG/CR4527, SAND86-0336, vol. 2. Sandia National Laboratories. Coutin, M., 2007. Phenomenological description of actual electrical cabinet fires in a free atmosphere. In: 11th International Fire Science and Engineering Conference, Interflam, London (UK), pp. 725–730. Coutin, M., Plumecocq, W., Melis, S., Audouin, L., 2012. Energy balance in a confined fire compartment to assess the heat release rate of an electrical cabinet fire. Fire Saf. J. 52, 34–45. Hamins, A., Johnsson, E., Donnelly, M., Maranghides, A., 2008. Energy balance in a large compartment fire. Fire Saf. J. 43, 180–188.

115

Huggett, C., 1980. Estimation of rate of heat release by means of oxygen consumption measurements. Fire Mater. 4 (2), 61–65. Le Saux, W., Pretrel, H., Lucchesi, C., Guillou, P., 2008. Experimental study of the fire mass loss rate in confined and mechanically ventilated multi-room scenarios. In: Fire Safety Science-Proceedings of the 9th International Symposium, Karlsruhe (Germany), pp. 943–954. Mangs, J., Keski-Rahkonen, O., 1994. Full scale fire experiments on electronic cabinets. VTT publications, 186. Technical Research Centre of Finland. Mangs, J., Keski-Rahkonen, O., 1996. Full scale fire experiments on electronic cabinets II. VTT publications, 269. Technical Research Centre of Finland. Mangs, J., Paananen, J., Keski-Rahkonen, O., 2003. Calorimetric fire experiments on electronic cabinets. Fire Saf. J. 38 (165–186). Melis, S., Audouin, L., 2008. Effects of vitiation on the heat release rate in mechanically-ventilated compartment fires. In: Fire Safety Science-Proceedings of the 9th International Symposium, Karlsruhe (Germany), pp. 931–942. Pagni, P.J., Shih, T.M., 1977. Excess pyrolysate. In: 16th Symposium (International) on Combustion, Massachusetts (USA), pp. 1329–1343. Peatross, M.J., Beyler, C.L., 1997. Ventilation effect on compartment fire characterization. In: Fire Safety Science-Proceedings of the 5th International Symposium, Melbourne (Australia), pp. 403–414. Plumecocq, W., Coutin, M., Melis, S., Rigollet, L., 2011. Characterization of closeddoors electrical cabinet fires in compartments. Fire Saf. J. 46, 243–253. Pretrel, H., Le Saux, W., Audouin, L., 2012. Pressure variations induced by a pool fire in a well-confined and force-ventilated compartment. Fire Saf. J. 52, 11–24. Suard, S., Nasr, A., Melis, S., Garo, J.-P., El-Rabii, H., Gay, L., Rigollet, L., Audouin, L., 2011. Analytical approach for predicting effects of vitiated air on the mass loss rate of large pool fire in confined compartments. In: Fire Safety Science-Proceedings of the 10th International Symposium, Maryland (USA), pp. 1513–1524. Werner, W., Angner, A., Röwekamp, M., Gauvain, J., 2009. The OECD fire database – conclusions from phase 2 and outlook. In: 20th International Conference on SMIRT, 11th International Post Conference Seminar on Fire Safety in Nuclear Power Plants and Installations, Helsinki (Finland). Werner, W., Hyslop, J.S., Melly, N., Bertrand, R., Röwekamp, M., Huerta, A., 2011. Enhancements in the OECD fire database – fire frequencies and severity of events. In: 21th International Conference on SMIRT, 12th International PreConference Seminar on Fire Safety in Nuclear Power Plants and Installations, Munich (Germany).