Journal
of Occupational
Elsevier
Science
THE DESIGN
E.M.
Accidents,
Publishers
B.V.,
8 (1986)
215
215-224
Amsterdam
-
Printed
OF HEAD PROTECTION
in The Netherlands
FOR TASKS
HICKLING
Institute
for Consumer
Loughborough,
Ergonomics,
Leicestershire,
Loughborough
LEll
3TU
University
of Technology,
(U.K.)
ABSTRACT Hickling, E.M., 1986. The Accidents, 8: 215-224.
design
of head
protection
for tasks.
Journal
of Occupational
An example of the importance of head protection design being related to the task of the wearer is given. The factors which determine the attributes of a task specific design are given and ways for measuring these factors are discussed. Examples of design specifications arising from these techniques are also presented.
INTRODUCTION
If, in the name of higher protection, it was suggested that the professional jockey should wear a motorcyclist’s full-face helmet, he would no doubt view the suggestion as absurd or misjudged. To win and be safe when racing, the jockey needs peripheral vision to gauge the distance laterally to adjacent horses. Additionally, he (or she) needs the ear uncovered in order to hear horses coming up behind and to judge the condition of the turf. Possibly he may wish to shout to spur his steed on still faster. The motorcyclist’s helmet would impede hearing, restrict vision and muffle even shouted speech. Additionally, when the jockey leaned forward out of the saddle, the greater mass of the motorcycle helmet would be at the least uncomfortable and probably produce uncontrollable nodding of the head with the jolting of the horse. This somewhat unlikely scenario is given to demonstrate that, in practice, the design of head protection should be a compromise between protection performance and functional performance for the wearer. A functionally designed item of protective headgear may be defined as one which minimizes impediment to the wearer’s activity and, where appropriate, facilitates the undertaking of the work by the inclusion of specific features. For more common jobs, the relationship between functional design of the head protection provided and the wearers’ needs may be less close than are the design of the jockey’s skull cap to BS 4472 [l] and the climbing helmet to BS 4423 [2]. In both of these instances, the nature of the tasks is well
0376-6349/86/$03.50
0 1986
Elsevier
Science
Publishers
B.V.
216
defined and users have been closely involved in the formulation of the designs and standards. For workers in industry, the nature of tasks in terms of the required protection performance and the functional helmet performance has been less clearly defined. This is perhaps the reason why there are only two types of head protection available in the U.K. for industrial use. These are BS 5240 131 and BS 4033 241. The two are differentiated by the difference in levels of protection performance and the concomitant difference in the mass of the helmets and the required clearance above the crown of the head. In general, for simplicity of issue, either protection of one type or the other tends to be issued at a particular industrial or construction operation. In industry, there is at least as much difference between the tasks contained in the very many different types of work as there is between the helmeted motor vehicle driver and the horse jockey. This paper briefly discusses techniques which may be used to establish differences between jobs in terms of head protection and provide a reasonable number of designs of protection to meet the majority of needs. Additionally, design specifications which have arisen from the use of these techniques in the construction industry are put forward. FACTORS DESIGN
WHICH
DIFFERENTIATE
JOBS IN TERMS
OF HEAD
PROTECTION
The factors which distin~ish jobs one from another are given in Table 1. The relationships between these factors and helmet design factors in general are drawn out in a separate paper, Hickling [ 51. Clearly, every job may at different times possess different levels and mixes of the factors given in Table 1. Likewise, different jobs may possess the same levels and mixes of these factors from time to time. Thus, for any particular job, a design must be a compromise to meet the range of conditions encountered in practice. However, this compromise does not necessarily become substantially greater for a design to match the requirements for a number of jobs. Should the number of jobs become too large, however, the risk of the design becoming inappropriate becomes greater. An adequate and successful design will, for a group of jobs, therefore be one which is suitable for use in each. The techniques for achieving this optimum are many. At one extreme is the inexpensive single opinion of the designer, which can be prone to bias, from prejudice, limited outlook and particular experiences. At the other extreme lies the more time-consuming survey of job ~quirements by observation and measurement of objective and subjective factors such as those discussed in Hickling [ 5] . Hickling [6] has established that a technique based upon a discussion among experts can lead to an economical technique less prone to bias and prejudice than that produced by a single designer’s or an expert opinion. By the systematic recording of discussion, details of a series of helmet specifications can be produced for a large number of jobs.
217 TABLE
1
Protection
and functional
considerations
Head hazard
Environment
Task
related
needs
TABLE
2
Choices
of feature
Design
feature
Helmet
shell
in the design
-
magnitude location of impact on the head likelihood of occurrence type, e.g. struck by, strike against
-
space in which work occurs climatic conditions hygiene conditions other hazards, e.g. noise, dust etc.
-
workload rate posture speech audition vision tool equipment use the use of the helmet cap lamp
given to the discussion Choices Omit
group
available
Omit
5 specifiable
Omit
Peak
Occipital or nape protection
Omit
Include
Gutter
Omit
Include
Nape strap
Omit
Shallow
Sweatband
Omit
Include
Omit
Include
Chinstrap
Omit
Include
Hearing Neck
protection
apron
Cap Augmented Anorak
ventilation
e.g. “carrier”
for a
specifications
Motorcycle
brim
Deep
Single
anchor
Omit
Goggle
l/zface visor
Omit
Ori-nasal
Full
Omit
Ear defenders
Ear plugs
Omit
Include
Omit
Skull
Omit
Include
Omit
Include
cap
type
areas Full
Draughtband
protection
for protection
Hemisphere
Peak
Eye protection
as a tool,
etc.
for specification
Localized shell strengthening
Respiratory
of head protection
face mask
Balaclava
Double Full
anchor
face visor
218 GROUPING
OF JOBS
For each of 178 jobs in the construction industry, safety and training officers specified a series of helmet and headgear design features based upon the wearer’s needs. This was done considering all the factors given in Table 1. These design features, which could be brought together to form specifications, are listed in Table 2. To aid the discussion, different features were displayed as required on a board, see Fig. 1. To analyse the information gained from the discussions, a simplified manual technique of cluster analysis was used. That is, a means of grouping jobs according to similarities and differences in helmet specifications. More formal statistical techniques of analysis are available as explained and discussed in Anderberg [7]. In 17 instances, the experts considered that one specification would suffice for a number of jobs. This left only 13 jobs with specifications unique to themselves. It was considered that 6 basic protection specifications would be the maximum which could be reasonably expected to be implemented in practice. Thus, the 6 specifications were identified as those which contained the largest numbers of jobs. Hence, the 6 largest groups of jobs were nominated as the core for each group. These 6 accounted for 94 of the 178 jobs. Each remaining specification and associated job(s) were then assigned to one of the 6 with the specification closest to it. In this manner each of the 6 core groups were enlarged to form 6 clusters of jobs. To examine the stability of these clusters, the above process was repeated,
Fig. 1. Head protection tion for each job.
design
features
as displayed
on a board
for building
a specifica-
219 TABLE
3
Groupings
obtained
by means
of manual
cluster
analysis
Group
1
All crane, banksman,
lift and derrick slinger, etc.
Group
2
On-site construction vehicle drivers - excluding Group 1.
Group
3 and 4
All personnel whose work layer, cable layer, etc. Exposed overhead workers, roofing workers, etc.
Group
Group
5
6
All indoor workers. Painters and decorators whilst on site.
-
operatives
and
is mainly e.g.
indoors
and
associated
self-propelled
associated
scaffolder,
personnel,
mobile
with
and outdoors.
All outdoor workers not mentioned in Groups trades, general operatives, and site equipment
machinery
trenches,
steeplejack,
Road
e.g.
steel
vehicle
e.g. pipe erector,
drivers
1 to 5 including skilled maintenance personnel.
in turn, using the specifications associated with the 5 largest groups and the 7 largest groups of jobs. Using 5 core groups, 2 of the previous clusters merged leaving the other 4 unchanged, i.e. the 4 clusters remained stable. Using 7 core groups, all the previously recognized clusters disintegrated to form 7 unrecognizable clusters. Six job groups were therefore constituted. Unexpectedly, and quite fortuitously, the characteristics of each group could be easily described as given in Table 3. Groups number 3 and 4 were the two which merged upon reducing the number of allowable clusters to 5. HELMET
SPECIFICATIONS
As a result of the process of job grouping and its subsequent validation and elaboration in a study performed by observation and questionnaire on 29 construction sites, specifications for helmets were drawn up. These are shown in Table 4. Table 4 shows that certain features are required irrespective of which group of jobs is being considered. For example, the requirement for high retention and a chinstrap reflect the universal existence of provocations to helmet retention. The reason for the differences specified are not all readily apparent. For example, trench and overhead workers require a visor, due to the critical need for better peripheral visual performance in comparison with other groups. Peaks are universally problematic in terms of the space taken by them and reports of impeded visual field. The peak should be absent on helmets for craneage personnel, in part, to ease the frequently required access
220 TABLE
4
Helmet
specifications
for each job group
(X
= not required,
J
= required)
Head protection feature
Craneage personnel
Vehicle
Trench and overhead
Indoor
General outdoor
Peak
X
Low protrusion
Low protrusion
Low protrusion
Low protrusion
Goggles
Full visor
Goggles
Goggles
Ear protection
:
J
High Retention
J
Chinstrap
J
J J
J J J
J J J
J J J
Top profile
low
low
low
low
low
Ventilation
J J
J J
J
J J
J
X
Sweat absorption
J
J
J
J
J
Weight
low
low
low
low
low
Balaclava
Balaclava
Skull
Balaclava
Skull
0.8
1.2
0.8
0.8
0.8
1.5
2.5
1.4
1.1
1.8
Eye protection
Draught exclusion
Other cover
X
head
Impact protection Most likely median rank Greatest possible median rank
cap
cap
and egress from cabs and in part to enable the forehead of the helmet to be used with the head to manoeuvre slings and chains on loads, as in Fig. 2. Because of higher workloads and the consequently greater need to lose
Fig.
2. The peak
and forehead
area being
used to manoeuvre
a concrete
hopper.
221
heat, draught exclusion is not required for trench, overhead and outdoor workers. This is contrary to what one may expect as both groups of workers are in exposed environments. Similarly, less coverage of the scalp is proposed for wear in winter, i.e. skull caps were suggested rather than balaclavas. During the field work, differences in the level of impact protection required were obtained for each worker observed, Hickling [6]. This was done by classifying potential impacts according to the de~itions given in Table 5. TABLE
5
Definitions for potential ______.________~ Impact
level
Helmet
impact
levels
ascribable
to observed
jobs Rank
reaction
Low
A helmet will easily protect against such an impact. Without a helmet, the resultant injury is Iikely to be little more than inconvenient.
1
Medium
A helmet will mediate such impacts and without a helmet injuries would be severe and possibly fatal.
2
High
A helmet is unlikely fatal injuries.
3
to prevent
serious
or
value
These classifications are broad but robust in operation. That is, the judgement of magnitude is readily repeatable between observers and can be consistently applied. In addition to the magnitude of impact the probability of impact as judged by the observer was also recorded. This was done in two ways: the impact most likely to occur and the greatest possible impact. These two categories reflect the probabilistic nature of impact protection. In practice, it is likely that head protection will be provided to meet an impact level occurring between the most likely and the greatest possible. Ideally, head protection would be designed to meet the greatest possible impact that could occur. In all groups, the most likely impact is well within the capabilities of existing helmet performance. However, the greatest possible impact varies significantly more than the most likely, and presents more problems in providing designs to meet these levels of impact, see Table 4. Field observations of helmet displacement were recorded. These are summarized in Table 6. This shows that the job groups associated with craneage and vehicle use suffer from more helmet displacements than statistically expected, due to minor collisions between the headgear and equipment or vehicles, see Fig. 3. In the case of craneage personnel this is due to the causes
222 TABLE
6
Incidence of causes for helmet displacements observed in each job group contribution to the overall Chi square significance is indicated in brackets)
(the
Source of displacement
Row total
Job 1
Posture Manipulation of materials Competition for space with equipment and vehicles
group 2
-.
189
85
1
3
4
5
169
493
720
939
7
19
23
28
88
12
24
35
33
188
10
(lY%)
percent
(iZ%)
6 2645
Competition for space with temporary structures Competition for space with permanent
5
0
11
55
32
69
172
structures
0
0
2
34
145
58
239
625
955
Column
total
240
134
201
x2 = 428.43, TABLE
1177
3332
df = 20, sig. @ p < 0.001
7
Incidence of displacement force position observed on helmets in each job group cent contribution to the overall Chi square significance is indicated in brackets) Helmet
location
Job
Row total
group
1
(the per-
2
3
4
5
6
Peak Back
65 57
33 26
57 44
172 128
316 (&%)
326 240
969 582
Top
(Zf%)
47
64
184
334
351
1043
29 26
11 17
17 19
69 12
70 148
122 138
318 420
240
134
201
625
955
1177
3332
Left side Right side Column
total
x2 = 18.405,
df = 20, sig. @ p < 0.001
previously mentioned. For vehicle drivers this is due to the restricted access to vehicles. If helmets are to be successfully worn without repeated donning and doffing during work, then more headroom and greater clearance on cant
223
Fig. 3. Helmet ing vehicles.
displacement
Fig. 4. A plasterer helmet
contacting
can
occur
experiencing helmet the plaster work.
by collision
displacement
with
cant
rails when entering
and spoiling
of his work
or leav-
by the
rails is required in vehicle cabs. Table 7 shows that displacement occurs in the craneage group on the helmet top more often than statistically expected. This is again due to cab cant rails and wearers manoeuvring slings and chains with their heads. For indoor workers, a lower than statistically expected frequency of helmet displacement occurs at the back of the helmet. This can be explained by the absence of scaffolding and high collars on outdoor clothing, both of which tend to displace a helmet at the rear of the head. Nevertheless, the bulk of the helmet remains a problem at the helmet front and sides for indoor workers, see Fig. 4. CONCLUSIONS
The careful use of expert judgements in discussion groups can provide a useful basis for determining designs of head protection. Additional information using techniques of subjective observation can provide a basis for judging impact protection and retention requirements (although in the case of the former, these do not constitute a full substitute for detailed statistical analyses of the actual type of injury and its severity with the source of impact). Additionally, a clear need for more fundamentally different designs of helmet than are currently available is indicated in the U.K. construction industry. In the case of the jobs which have been studied in this instance, some radical departure in design would ensure a helmet better suited to the job. Additionally, the large incidence of potential helmet displacement indicates the need to improve retention performance for certain groups of users.
224 REFERENCES 1
British Standard 4472, 1969. Protective skull caps. British Standards Institution, London. 2 British Standard 4423, 1969. Climber’s helmets. British Standards Institution, London. 3 British Standard 5240, 1975. Safety helmets for industrial use. British Standards Institution, London. 4 British Standard 4033, 1966. Industrial scalp protectors (light duty). British Standards Institution, London. 5 Hickling, E.M., 1986. Factors affecting the acceptability of head protection at work. Journal of Occupational Accidents, B(3): 193-206. Hickling, E.M., 1986. An investigation on construction sites of factors affecting the An investigation on construction sites of factors affecting the 6 Hickling, E.M., 1985. acceptability and wear of safety helmets. Institute for Consumer Ergonomics, Loughborough University of Technology, Loughborough, U.K. 7 Anderberg, M.R., 1973. Cluster analysis for applications. Academic Press, New York.