Study of the physiological effects of wearing breathing apparatus.

SUMMARY
1. A two stage study of the use of breathing apparatus (BA) in the fire service has: (i)
identified areas of task and those particular protective equipment combinations,
common to fire brigades, likely to cause problems to firefighters and to require more
detailed investigation; (ii) quantified the degree of the effects of different
tasks/protective equipment in relation to safe working practice by measuring
physiological and subjective performance under conditions simulating severe physical
and thermal conditions, as a means of assessing both the physiological effects on
firefighters of wearing BA and the adequacy of existing apparatus.
2. The first stage consisted of a questionnaire study of brigades and operational
firefighters. An initial set of questions was drawn up and six stations in three
brigades were visited (Lothian and Borders, Humberside and Greater Manchester).
Structured interviews with senior personnel, including BA training officers, and
firefighters were carried out, in order to obtain more detailed information about some
of the likely problems associated with particular task/equipment combinations
identified by firefighters. These were intended to allow the research team to devise
a comprehensive questionnaire on problems associated with donning and using BA
during training and operational duties. Every local authority brigade in the UK and
over one thousand wholetime operational firefighters were sent questionnaires.
Factual information about BA usage and problems associated with use of BA in
relation to tasks and other protective equipment was obtained. All brigades
responded to their questionnaire and 76.3% of firefighters from one in six stations,
selected randomly from all stations in the country, responded to the firefighters’
questionnaire.
3. Most (95%) firefighters used BA less than once per week, 31% had worn BA for a
toxic substance spillage at least once during the last year and 23% had attended a
flammable substance leak, none more frequently than once per week. Only 6% of
firefighters had needed to change their BA cylinder on more than twelve occasions
in the last year. The most widely used open circuit sets (OCBA) were Draeger PI 12
(30%), Interspiro Spiromatic (23%), Sabre Centurion (14%) and Siebe Gorman
Firefighter 1 and 2 (10% each).
4. Problems with donning and using the sets were reported by users of all types of BA.
On average about a quarter of all users reported problems related to the weight and
size of the set, difficulty with the facemask seal and visibility and interactions with
other protective clothing, such as gastight suits. Problems were also caused by
interactions with clothing and other personal items, such as helmets (37%) and gloves
(57%). Users of Sabre Centurion sets reported the least number of problems,
whereas users of Siebe Gorman Firefighter 1 were most dissatisfied. No information
was obtained about the only closed circuit BA (CCBA) in use in the fire service, as
none of the stations using it were included in the random selection process.
5. Following discussions with the Fire Research and Development Group of the Home
Office, twelve brigades were selected for subsequent physiological studies from those
using the four OCBA types in most widespread use. Brigades were asked to supply
a list of at least twelve volunteers (firefighters or leading firefighters) in age bands:
less than 25; 25 to 35; and over 35 years. One team of four firefighters, in the ratio
of 1:2:1, according to these age bands, was selected by the IOM from each brigade.
Additional teams were selected from Kent (two extra teams using Sabre SEFA
CCBA), London (four teams, including two each with 50% female firefighters) and
Essex (two teams). A long duration (lightweight) BA was not available in operational
use at the time of this phase of the study and could not therefore be included.
6. In total 72 firefighters (eighteen teams) participated during nine different weeks in the
physiological studies, which took place over four days at the Fire Service College,
Moreton-in-Marsh. On each morning at the same time subjects undertook a series
of five minute walks at 5km h”1
on an inclined treadmill (average room temperature
22°C), while wearing either tee shirt and shorts (PE kit), full firefighter’s turn out
gear (firekit), firekit and own BA, or firekit and own BA with lightweight cylinder.
Details were obtained on height (mean = 1.79m), age (mean = 31 years), skin fold
thicknesses at four body sites (for body fat determination [mean = 17%]), smoking
habit (26% smokers) and length of fire service employment (mean = 8 years).
During each exercise heart rate (HR), inspired air volume, % oxygen and % carbon
dioxide in expired air were recorded at minute intervals: the oxygen uptake (VoJ,
(the volume of oxygen consumed per minute) and volume of air expired per minute
(VE) were subsequently derived. HR and Vo2 were examined in relation to factors,
such as workload, presence of firekit and BA and type of BA.
7. Firekit and BA in combination increased Vo2 from 2.0 to 2.7/ min”1
(35%) and HR
from 124 to 158 beat min”1
(27%) at the steepest treadmill gradient used (7.5%), each
factor contributing almost equally to the increased response. Replacement of the
standard llkg air cylinder used in OCBA by a lightweight (6.5kg) cylinder reduced
Vo2 slightly (O.I/ rnin”1
) and HR significantly (6 beat min”1
). Vo2 was significantly
lower (by about 0. II min”1
) among users of Sabre Centurion, compared to other types
of BA. HR was also lower, by 6 beats min”1
, but this difference was not statistically
significant.
It was not possible to obtain reliable estimates of maximum aerobic capacity
(maximum oxygen uptake, Vo2 max) from all the participants in this study. This was
principally because it was necessary to set relatively low workloads on the treadmill,
in order to examine the additional physiological response to wearing clothing and BA.
If the workloads had been set too high for the no BA/clothing tests, many participants
would have been unable to complete the tests when BA and clothing were worn.
However, from the limited range of measurements available, the estimated average
indirect Vo2 max in this study group was 3.71/ min”1
(equivalent to 46.4m/ min”1
,
when corrected for average body weight). This is slightly greater than the fitness
level (3.45 [43.7]) observed in a recent nationwide survey of firefighters with similar
average age and body weight to those in the present study, indicating that more fitter
individuals may have volunteered than the less fit or that the general fitness level of
firefighters has improved during recent years.
8. On consecutive afternoons the participating teams carried out three exercises designed
to simulate different aspects of firefighters’ duties requiring BA and exposure to
combinations of heat and physical workloads. These scenarios were devised in
conjunction with fire officers/instructors from the BA Training School at the Fire
Service College. They consisted of a short duration (20-30 minutes) search and
rescue exercise in a two storey building, containing an intense live fire; removal of
heavy chemical containers following a toxic substance spillage, for example, at a road
accident and requiring use of a gastight suit; and a longer duration (approximately 1
hour) search through an industrial complex containing a live fire requiring re-entry
after the replacement of the BA air cylinder, all under trained supervision.
9. The first exercise led to very high heart rates (over 200 beats min’1
in at least one
member of 50% of the teams), body temperatures (over 40°C in at least one member
of two thirds of the teams) and sweat rates (averaging 2.5/ per hour). The chemical
spillage exercise lasted 20 minutes and led to a modest rise in body temperature,
which only occasionally rose above 38°C, but a more substantial increase in heart rate
(five over 200 beats min’1
). The long duration exercise caused high heart rates (40%
of firefighters greater than 200 beats min’1
) and body temperatures which rose to
unacceptably high levels (> 39.5°C) in members of one team only (Sabre SEFA). Air
consumption, expressed as volume of air used per minute (minute volume), averaged
43, 57 and 42/ min’1
respectively for the three exercises. No clear differences in
physiological responses were observed between users of different BA during these
exercises. However, although Sabre Centurion users included the team with the
highest average heart rate and increase in body temperature during the short duration
exercise, this group also had a lower minute volume, 437 min”1
, compared to the other
teams, whose average minute volumes ranged from 48 to 51/ min’1
.
10. Ergonomic assessment of the four sets in most common use suggested that the Sabre
Centurion, by virtue of the position of its centre of gravity in relation to the wearer,
was biomechanically more efficient during dynamic movements typical of training
exercises or operational incidents. The Draeger PI 12 was almost as good in this
respect but the Interspiro and Siebe Gorman sets had second moments of inertia (a
measure of the energy needed to move the BA when worn) twice as great as the other
two sets and they would therefore require greater muscular effort by the firefighter
to control his body during movement. The backplates of these four sets in current
use tend to be too long for the range of wearers. A newer Draeger model (P90) has
a considerably shorter backplate which would conform to the 99th percentile male
back length but would still be too long for the 95th percentile female user.
11. In conclusion, about a quarter of all UK firefighters experience minor or major
problems related to their BA, mainly associated with the weight or size of the set and
adverse interactions with other personal equipment. Some types of BA are much
more acceptable to their users than others. To a limited extent we have found that
the additional physiological response caused by wearing BA is less amongst
firefighters wearing the BA reported in the questionnaire as giving the least problems
in use. The physiological response of firefighters to realistic training exercises
requiring BA leads to unacceptably high heart rates, and body and skin temperatures
in many cases. Consideration should therefore be given to providing physiological
monitoring in such exercises. Manufacturers of BA for fire service use should
continue to develop equipment that minimises additional physiological, including
musculoskeletal, strain. This can be achieved by reducing cylinder weights and
designing sets that allow the BA’s and the body’s centres of gravity to be as close
together as possible. Making the size of BA, particularly the length of the backplate,
more appropriate to the users’ dimensions should then reduce the amount of
complaints from firefighters. However, design of BA must be considered in the
context of other essential clothing and equipment used by the firefighter