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Value of a fire detector in the home
NATIONAL RESEARCH COUNCIL CANADA
DIVISION O F BUILDING RESEARCH
THE VALUE OF A FIRE DETECT OR IN T H E HOME by J. H. McGuire and B. E. R u s c o e F i r e Study No.
9
of the Division of Building R e s e a r c h OTTAWA December 1962THE VALUE OF A
FIRE
DETECTOR IN THE HOME byJ. H. McGuire and B. E. Ruscoe
SUMMARY
The circumstances in which 342 persons lost their lives in Ontario dwellings as a result of f i r e have been examined and estimates made of the likelihood that each might have escaped had either an ion- ization chamber or a simple thermal f i r e detector been operating at the time.
The over-all result i s that the estimated saving of life would have been 4 1 and 8 per cent for the ionization chamber and thermal detectors respectively.
. Brief reference i s also made to the economy of installing a
f i r e detector with a view to reducing property damage.
In the Province of Ontario deaths resulting from f i r e s in buildings, or from the ignition of clothing, average about 175 per year, or 3. 1 per 1 0 0 , 0 0 0 head of the population. Of this average total of 175,
about 115 of the victims died a s a result of a f i r e in a residential building (excluding deaths resulting from the ignition of clothing). A reduction of the life r i s k associated with residential property would thus greatly reduce the over -all incidence of death by fire. With a view to achieving this object ,many people have recommended a m o r e widespread use of fire-detector alarm systems in residential properties.
The object of the work described in this report was to estimate the effect on the f i r e death r a t e of the installation of f i r e detectors in one
class of residential property. The work was made possible by having access to the card index system and files set up during the course of a much more comprehensive program of work aimed at analysing the causes of fire deaths (1).
METHOD
The installation of f i r e detectors and a l a r m s in residential properties i s r a r e ; thus it i s not to be expected that the f i r e death
analysis, already r e f e r r e d to, involving a total of about 1,000 deaths (about 175 a year for 6 years), would yield any significant information on the m e r i t s of such systems. The approach planned for the present study was to use an estimate of the effect that a f i r e 'detector would have had in each individual incident. Such an estimate was not included in the card index system previously used, which was confined to factual information. Nevertheless, the information on the c a r d s frequently allowed an estimate to be made, and in the remainder of the cases indicated the p r e c i s e location of the file containing further information, newspaper cuttings, etc. The accuracy of the estimate a s to the hypo- thetical effect of a f i r e detector at each incident i s open to question;
since i t depended on the judgment of the authors. It i s worth recording however that, in sample surveys conducted independently, the author s t ratings corresponded remarkably well. T o illustrate the procedures adopted the relevant m a t e r i a l on which estimates were based in t h r e e sample cases has been included in Appendix A.
Two types of detectors were considered, one an extremely sensitive, ionization chamber, smoke detector and the other a fixed temperature (150°F) device assumed to have a response typical of a bimetal deyice with a s low a s possible a thermal-capacity
/
surface- a r e a r a t i o for such a type. The performance characteristics of such a fixed temperature device a r e well known; a number of experiments w e r e performed with the smoke detector to give some experience and f a - miliarity with i t s behaviour.
There i s some likelihood that r a t e of r i s e detectors might be installed in residences but no simple basis was developed for e s t i - mating their response times under the various conditions which prevailed. They were therefore not considered in this survey. While their per
-
formance might have been superior to that of the "fixed t e m p e r a t u r e t t devices i t i s not likely that the superiority would have been a s marked a s in the case of the ionization chamber detector.A preliminary examination of some of the punched c a r d s indicated that a survey covering all residential properties would give r e s u l t s that were difficult to present and probably w e r e not accurate. The survey was therefore confined to the tlunshared separate dwelling. This reduced the number of deaths to be investigated to 342 covering the years 1956 -1960, or a yearly average of approximately 70. As previously stated, total f i r e deaths average about 175 annually of which 115 a r e the result of a f i r e in a residential building (excluding the c a s e of a I t clothing
f i r e " in a residential building).
It was assumed that fixed temperature detectors were much cheaper than the smoke detector and could, therefore, be used in greater numbers. Fixed temperature detectors were assumed to have been
installed a t the head of any s t a i r c a s e and, in each instance, in the a r e a of origin of the fire. Two smoke detectors were assumed to have been used, one a t the head of the basement s t a i r s and one a t the head of the main s t a i r c a s e in a 2-storey dwelling or between the living and sleeping a r e a s in a 1 -storey dwelling.
In every case considered the possibility of saving life was estimated according t o one of the following s i x ratings: 100, 75, 50, 25, 0 p e r cent, and unknown. The use of ratings between 100 per cent and z e r o can be justified on the grounds that purely factual information indicates that, under remarkably s i m i l a r circumstances, one individual will die while another will save himself. A number of c a s e s in which this principle was invoked involved the vi c t i m l s falling asleep while
smoking, followed by the ignition of the bed, chesterfield, etc. on which he or she was lying.
Besides the above ratings for each individual death, the following information was recorded:
1. Year ( a ) 1960 (b) 1959 ( c ) 1958 (dl 1957 ( e ) 1956
2. Nature of wall and ceiling linings (a) Incombustible (b) Combustible ( c ) Mixed (d) Unknown 3. Nature of victim ( a ) Average adult
(b) Child under 7 years old, infirm person, o r adult 80 or m o r e y e a r s old
( c ) Unknown
4. Location of origin of f i r e
( a ) Other than basement (b) Basement
( c ) Unknown
.
Circumstances surrounding origin of f i r e ( a ) P e r s o n falling asleep while smoking (b) Improper u s e of flammable liquids ( c ) Intoxication of victim, or adultresponsible for victim (d) Other
6. Condition of responsible adult ( a ) Asleep
(b) Awake ( c ) Unknown
RESULTS
Table I summarizes the most important r e s u l t s of the analysis.
TABLE I
SUMMARIZED
ANALYSISIn addition t o the 326 c a s e s mentioned in Table I, a further 16 fell is the category "death due t o f i r e in an unshared dwelling, I ' but they w e r e
disregarded because lack of information precluded any estimate a s t o the possible effect of a f i r e detector.
Victim
F o r the sake of completeness the m o r e detailed table which was originally prepared i s also included ( s e e Table 11). It indicates
1. that the total number of deaths considered is sufficient t o give the r e s u l t s of Table I some meaning.
Deaths
2. that the value of f i r e detectors in saving lives, on a p e r centage basis, does not depend appreciably on the nature of the internal linings of dwellings.
This does not mean that the saving of life p e r 1,000 installed f i r e detectors would be independent of the linings in dwellings. An evaluation of this
P e r cent to be saved by smoke detector
-
-
-Average Adult 181 T P e r cent t o be saved by t h e r m a l detector 4 5-
-
-35 4 1 Child, Infirm, etc.Total 8 7 8 145 326
feature would r e q u i r e a knowledge of the r a t i o of combustible to
noncombustible -lined dwellings in Ontario. It would be t r u e , however, i f the r a t i o w e r e equal t o the life loss ratio. It i s popularly thought that the incidence of f i r e s with accompanying life l o s s i s greater in
combustible-lined dwellings. If this w e r e t r u e then the saving of l i f e p e r 1,000 installed f i r e detectors would be greater for combustible
-
lined than for noncombustible-lined dwellings. On the basis of the r e s u l t s quoted the fractional saving of life compared t o c a s e s where no detectors a r e installed would be v e r y s i m i l a r .As stated in the previous section further information on
each incident was also listed. The most interesting end r e s u l t was that, of the 342 deaths investigated, 313 were associated with f i r e s not
originating in basements, 1 1 with f i r e s originating in basements, and 18 with f i r e s in which the s t o r e y of origin was unknown.
A number of the incidents in which poor ratings w e r e given t o the hypothetical effect of a f i r e detector w e r e associated with bad practice. The number of deaths falling in this category was 90 of which 21 resulted from the improper u s e of flammable liquids; 48 deaths w e r e associated with falling asleep while smoking, and 21 w e r e associated with intoxi-
cation. A death was considered t o fall in one or other of the latter two categories i f the c r i t e r i a "fell asleep while smoking, or "intoxicated" applied t o the victim personally or to the adult who could otherwise have attempted t o save a child, an aged o r infirm victim.
A factor of great i n t e r e s t i s the extent t o which a f i r e detector will protect a sleeping person. A breakdown of Table I giving informati.on on this question i s presented in Table 111. Thehtotal number of deaths included in Table I11 i s two fewer than in Table I because the available information in these two cases did not include a statement a s t o whether the victim or the responsible person was asleep.
The average f i r e -conscious individual generally believes that his r i s k of dying a s a r e s u l t of f i r e i s greatest when he i s asleep and that a f i r e detector installation will greatly reduce this particular risk. Some comment i s therefore required on the estimated result, given in Table 111, that even the most sensitive f i r e detector available will only reduce t h e over a l l r i s k to a sleeping individual by a factor slightly above 2 (59 p e r cent).
TABLE I 1 1
EFFECT OF SLEEPING
One factor responsible in some s m a l l m e a s u r e f o r this low rating i s that 69 of the 205 deaths involved w e r e associated with the victim's falling asleep while smoking, or with intoxication. The expla- nation of the remaining deaths for which poor ratings w e r e assigned i s
p r i m a r i l y associated with the behaviour characteristics of human beings and with the fact that most deaths a r e caused by toxic gases or lack of oxygen, the onset of unconsciousness in these circumstahces being without warning. Death frequently occurs when victims delay leaving a building or re-enter it for various reasons such a s the r e s c u e of other individuals or valuable property, or need of warm clothing in subzero weather. Cases a l s o a r i s e in which the death of a would-be r e s c u e r r e s u l t s from t h e r m a l effects; a victim's failure t o leave the building i s often associated with the rapid development of the f i r e which cuts off his escape route.
Child,
Infirm, etc. Total
In m o r e than one case death could be attributed to the difficulty
in 'wakening the victim despite no extraneous influences. such as sleeping drugs. The difference between the ratings attributed t o the smoke and t o the t h e r m a l detectors (59 and 12 p e r cent respectively in the c a s e of
sleeping individuals) i s purely a function of the modes of operation of the two detectors, particularly in relation t o the f i r e that develops slowly. Such a f i r e will usually be detected a t a fairly e a r l y stage by an ionization chamber smoke detector. T o be detected by a thermally operated device of the type considered, a temperature of 150°F or m o r e must have developed
in the region of the detector. By the time such a condition has been established, 76 20 5 62 5 9 13 12 68 119 10 13 1 1 1
a s in the case of certain slowly developing f i r e s , l a r g e quantities of smoke have been generated which could make escape routes untenable or cause death even in a r e a s r e m o t e from the fire.
PROPERTY LOSS
The scope of this note i s p r i m a r i l y concerned with life l o s s in "unshared s e p a r a t e dwellings,
"
but a c u r s o r y examination of the economic value of a f i r e detector in reducing the over -all p r o p e r t y l o s s i s s o simple and yet s o informative that i t i s worth including.A convenient approach t o this problem would be t o consider the annual p r o p e r t y l o s s in Ontario associated with "unshared s e p a r a t e
dwellings.
"
This figure i s not available, but the r e p o r t s of the Dominion F i r e Commissioner indicate that residential p r o p e r t y l o s s e s i n Ontario for the period considered in this note a r e i n the region of $6,000,000.00 p e r year. A figure which m a y be taken to approximate the number of r e s i d e n c e s covered by the above figure i s the number of "householdstt in Ontario, a s defined by t h e Dominion Bureau of Statistics. Between1956 and 1960 this number ranged between 1, 390,000 and 1,590,000 s o that a f i g u r e of 1, 500,000 will s e r v e a s a n approximate a v e r a g e for the purposes considered h e r e .
T h e average f i r e l o s s p e r dwelling unit at r i s k , t h e r e f o r e , is
only $4.00 p e r annum. If f i r e detector installations w e r e a s s u m e d t o be 100 p e r cent effective in eliminating p r o p e r t y l o s s , and i f their lifetime w e r e a s s u m e d t o be 10 y e a r s , then universal installation in s m a l l r e s i d e n c e s would only prove economic i f the cost p e r installation w e r e l e s s than $40.00. The assumption of 100 p e r cent effectiveness involved in the above calculation i s such a substantial departure f r o m the truth, especially where low-cost. t h e r m a l l y operated detectors a r e considered, that the economic cost of a f i r e detector s y s t e m , f r o m the p r o p e r t y l o s s point of view, should be
considered t o be lower than $40.00 by a factor g r e a t e r than 2, and possibly a s high a s 10 o r m o r e . It i s probable that the installation of f i r e
detectors in s m a l l residential p r o p e r t i e s can only be economically justified f r o m the p r o p e r t y r i s k aspect in v e r y specialized c a s e s .
T h e s e calculations r e l a t e t o a total l o s s that includes l a r g e
residential p r o p e r t y l o s s e s , whereas the conclusion h a s been taken t o apply to s m a l l residential properties. T h e magnitude of the e r r o r i n the
SCOPE OF RESULTS
It cannot be overemphasized that the scope of this note is
confined to "unshared separate dwellings" and s m a l l residences. In such buildings a s schools, department s t o r e s , and warehouses, some f o r m
of f i r e detector can prove extremely valuable from either or both life safety and property aspects. Appendix B discusses briefly one or two of the
features which would suggest that the t h e r m a l detector would give a f a r better performance in a l a r g e r building than that predicted by the work described h e r e relating to the small dwelling.
REFERENCE
1. Williams -Leir, G. F i r e deaths in Ontario. In F i r e R e s e a r c h and F i r e Prevention, Proceedings of a confTrence held Oct. 1 t o 3,
1958, Ottawa. National R e s e a r c h Council, Division of Building
APPENDIX A
SAMPLE CASES
With a view t o clarifying the procedure by which estimates w e r e made of the likelihood that a f i r e detector might have saved a life, pertinent information relating t o t h r e e of the 342 c a s e s considered is given below. The f i r s t two examples w e r e picked a t random. Case 1 r e p r e s e n t s a c l a s s in which an accurate a s s e s s m e n t could be made with
only the minimum of information. Case 2 i s an example in which a reasonably accurate a s s e s s m e n t was possible from the information on the c a r d with
brief reference t o other m a t e r i a l such a s newspaper cuttings. Case 3 was not picked a t random but was selected to illustrate the s m a l l p r o - portion of cases in which a close examination of all the available m a t e r i a l was n e c e s s a r y before any a s s e s s m e n t could be made.
Case 1
In addition to giving, in coded form, the answers t o a number of routine inquiries the c a r d gave the following information: "It is believed victim poured coal oil into wood stove and was caught in the
resulting explosion. Victim rescued by neighbour (who lived approximately 1/2 mile away). Victim received s e r i o u s burns t o his hands and face.
It is thought he suffered a heart attack before he was overcome by smoke. He was asphyxiated. Victim lived alone. T h e r e was no f i r e department nearby.
F r o m the above comments it was immediately a s s e s s e d that t h e r e was no likelihood that either an ionization chamber o r a t h e r m a l detector installation would have p r evented this fatality.
Case 2
In addition t o the coded information, the following comments were on the card: "It i s believed victim had found the f i r e around midnight
caused by a cigarette smouldering in a chesterfield chair. He had doused chesterfield with water and threw cushion outside. He returned t o bed but f i r e smouldered. Body was found in a closed bedroom not n e a r f i r e .
"Victim died a s a r e s u l t of suffocation and was dead 2 t o 3 hours before a l a r m was turned in by a neighbour.
The most valuable information, additional to that given on the card, was contained in newspaper reports. Firstly, a photograph had been
reproduced which showed that the f i r e , or the smouldering, had been virtually confined t o the chesterfield. The second pertinent i t e m was that t h e r e had been s i m i l a r f i r e s in the house on at l e a s t two previous occasions and each t i m e the victim had been found in a smoke-dazed condition but had escaped s e r i o u s injury.
It would appear that the victim had been somewhat dazed,
principally by sleep, when he had made his f i r s t attempt t o extinguish the f i r e before r e t i r i n g again. These being the conditions prevailing, i t i s probable that the victim might not have responded t o an a l a r m given a t
almost any stage of the f i r e . The ratings given t o the t h e r m a l and ionization chamber respectively w e r e t h e r e f o r e 0 and 50 p e r cent.
Case 3
The index c a r d included the following notes: "Leak in a copper propane gas line. A kink had been formed in the line making the loop,
a t the top of the kink a c r a c k was found. T h e c r a c k had developed in the copper line and t h e gas had escaped, i t was ignited by the pilot light.
The pilot light r e f e r r e d t o was not immediately adjacent t o t h e c r a c k in the pipe and therefore ignition would only b e expected to have occurred when a n appreciable proportion of the volume of the room was within the flammable limits. Propagation throughout this volume would
constitute a n explosion and in fact another occupant of the house h e a r d a n explosive noise immediately p r i o r to his being a w a r e that the house was on fire. This and other accounts of the f i r e indicate that s p r e a d was v e r y rapid and a s the ceiling and wall linings throughout w e r e of wood such rapid s p r e a d i s possible.
In addition to the victim, the house was occupied by a 16-year
-
old brother and a 23 -year -old brother. At about 5:30 a. m. the 16 -year-
old heard what m a y be taken to have been the low explosion originating the f i r e . Almost immediately he got out of bed to investigate and saw flames downstairs. He yelled warning, attempted t o telephone the f i r e department, but had to leave the house before accomplishing this.Although the 23-year-old responded t o the warning yell, h e was unable to leave the house by the stairway and leapt f r o m h i s window.
On this evidence it was estimated that an a l a r m given by a t h e r m a l detector would not have saved the victim's life but that the f a s t e r response of an ionization chamber installation might have given a 50-50 chance.
APPENDIX B
THE THERMAL DETECTOR
The concluding paragraph of this note emphasizes that the
findings r e l a t e only to "unshared s e p a r a t e dwellings. 'I This appendix
d i s c u s s e s one or two of the f a c t o r s that make it likely that the poor performance expected of t h e r m a l detectors in dwellings does not allow the inference that a s i m i l a r performance i s likely where l a r g e r buildings a r e considered.
When a l a r g e building i s compared t o a s m a l l one i t i s usually found that the s t o r e y heights a r e v e r y s i m i l a r and that the sizes, of the r o o m s o r corresponding enclosures a r e not closely r e l a t e d to the s c a l e of the building. T h e s e r e m a r k s a r e p a r t i c u l a r l y appropriate when comparing a dwelling and a l a r g e hotel. Generalizing and approximating, i t m a y t h e r e f o r e b e said that a f i r e detector will detect a f i r e when i t h a s attained a specified
"magnitude1' r e g a r d l e s s of the s i z e of the building. Even when a l a r g e unpartitioned building i s involved, the c r i t i c a l "magnitude" of f i r e which
can be detected will not i n c r e a s e in proportion to the scale of the building. The principal feature that leads to a prediction of a poor
performance for the t h e r m a l detector in the home i s that, in the m a j o r i t y of c a s e s , a dwelling would be heavily charged with smoke, throughout,
by the t i m e the a l a r m was sounded. The r e f e r e n c e s t o s c a l e given above
make t h i s statement inapplicable td l a r g e r buildings. F o r this r e a s o n alone, therefore, a better performance i s to b e expected f r o m the point of view of life safety in l a r g e buildings.
A better performance f r o m the point of view of p r o p e r t y protection
i s a l s o to be expected because the f i r e in the l a r g e r building will be detected when it i s proportionately s m a l l e r in comparison with building s i z e and because, in general, the subsequent development of the f i r e will be slower, again in comparison with the s i z e of the building.
