Emergency lighting not so safe

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Publisher’s version / Version de l'éditeur:

Lighting Magazine, 6, 1, p. 22, 24, 1992-02

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Emergency lighting not so safe

Ouellette, M. J.

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IRC PUB

Emergency Lighting Not So Safe

by M.J. Ouellette

Reprinted from

Lighting Magazine

Vol. 6, No. 1, 1992

pp. 22, 24

(IRC Paper No. 1740)

NRCC 331 28

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Emergency

Lighting

Emergency

lighting

not so safe

The National Research Council recently surveyed seven buildin s'emergency lighting systems in

Ottawa and found some wide variations in safety standards. T

k

is

report, exclusive to Lighting

Magazine, describes the findings

by Michael Ouellette, NRC O t t a w a

i

A

fter thoroughly in- vestigating seven

c.

Ottawa office buildings, we found the emergency lighting in them was extremely variable.

Some areas of evacuation, including stairwells, were totally dark. Some areas were sufficiently dim to jeopardize the efficiency of building evacuation.'. Other areas had more than enough lighting for an emergency.

The adequacy of emergency lighting was par- ticularly variable in open plan offices where floor layouts were reorganized without aligning the emergency ceiling light fixtures with new aisles and exit routes.

Study's objectives

1000

M S H rmgulutlen, 10 Lux maan

g

800 z

e

Q

600

V)

n

0 +

400

Q

n

E

=

200 z

0 (0.1

1

10 100 1000

lllumlnancs

(Lux)

Fig. 1 : Binned illumina- tion data collected at one meter intervals along the centres of all exit routes of ran- domly selected floors from each of the sur- veyed buildings. Meas- urements were col- lected at a height of one meter above floor level, in accordance with COSH regula- tions.

The primary objective of the study was to determine whether the buildings surveyed would meet the illuminance requirements specified in Labour Canada's Canadian Occupational Safety and Health (COSH) regulations.2 However, we found that because of the variable and skewed distributions of emergency lighting data, it would be

L

impossibleto reliably characterizetypi- cal emergency illumination in terms of the COSH regulations, which are defined, in part, according to the arithmetic mean of four "representative" illuminance measurements.

Arithmetic means do not reflect the

wide range of illuminances actually found in the surveyed buildings (Fig. 1 ), especially for sample sizes as smaJI as four.*

As an analogy, if three workersearn $1 0,000 annually while their employer earns $1 70,000, then it would be misleading to say that the four of them earn $50,000 on average. That would classify them all as middle incomeearners, whereas in reality, three of the four earn poverty wages and may well require immedi- ate attention.

Likewise, we found that mean illuminance was strongly influenced by the relatively few brightly il- luminated areas near and directly below the sparsely spaced luminaires. From Table I (page 24),

*Manufacturers of illuminance meters typically claim that their instruments will measure illuminance at a single point to an accuracy of plus or minus 10% or better. However, for the observed distributions, over 390 unbiased measurements are required to obtain a mean which is accurate to within

lo%, 19 times out

o f

20.

one might wrongly conclude that the emergency lighting systems in six of the seven buildings were suitable since they provided a mean of ap- proximately 10 lux or more. In reality, exactly half of the surveyed spaces had one lux or less of emergency illumination (median, Table I), and 14% of the surveyed exit routes were in darkness or below the limits of sensitivity of our photometric equip- ment (0.1 lux).

In these portions of the exit routes, it would be difficult for people to find their way to safety with the emergency lighting systems currently in place. This became quite apparent to one member of the lighting survey team who, in spite of all precautions, fell over a potted fern while conducting his measurements.

Consequently, it is recommended that regulations, codes and standards on emergency lighting should not be based on means, but instead on statis- tics which are less sensitive to dis- tribution shape and variability.

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Emergency

Lighting

-

I I

Building#

n

Mean

Md

SD

Min

Max

MaxIMin MeanIMin

1

57

89 ₂₇

₁₁₅

6

396

66 ₁₅

Corn

bined

4540

15

1

39

0.1

548 5480

150

Table I. Summary of illuminance measurements expressed as number of measurements (n), arithmetic mean (Mean), median

.

(Md), standard deviation of the mean (SD), minimum (Min), maximum (Max), and uniformity ratios (Max/Min and Mean/Min).

Medians or minimums would be more suitable. Indeed, some codes

and standards around the w o r ~ d ~ . , ~ . ~ ~ . are already based primarily upon

minimums.

Safety practices

Regarding practices in the individual buildings, we found that building operation personnel routinely tested and inspected the operation of their central emergency power systems in accordance with the National Fire Code of ~ a n a d a . ~ . However, it appeared that less attention was placed on ensuring that central emergency power culminated in the delivery of emergency lighting where needed.

Large sections of emergency evacuation routes were in complete darkness during the survey. Causes of darkness included 1) failed lighting units, 2) absence of lighting units and,

, quite frequently, 3) blockage of emer-

gency lighting by newly erected walls and privacy panels.

Building operation personnel could not distinguish normal lighting fixtures and circuits from those con- nected to central emergency power. Consequently, walls and partitions were routinely erected in disregard of emergency lighting requirements.

Where battery powered unit equip- ment was provided, many of the units were triggered on general purpose circuits rather than on lighting circuits. Thus, if lighting failed in these spaces independently of the general purpose circuits, the evacuation routes would receive no emergency lighting.

It is impossible, from this survey of only seven randomly selected buildings, to draw conclusions about the general state of emergency lighting across Canada. Nevertheless, the findings call attention to some very important aspects of building safety that may, on occasion, remain over- looked.

Based on our observations, it is recommended that safety in large buildings could be improved with the adoption of the following practices: *entire emergency lighting systems

(including individual fixtures) should be routinely tested and inspected;

*building specification and commis- sioning procedures should ensure adequate emergency lighting in evacuation routes when normal

lighting circuits fail (thus, local bat-

tery powered units should be trig- gered on lighting circuits rather than general purpose circuits;

.emergency lighting fixtures should be discerniblefrom the normal light- ingfixtures (e.g., by a coloured stick- er on one corner of each unit); *operations policies should ensure

that these fixtures receive main- tenance priority and that floor plan changes, such as the erection of partitions, do not defeat the effective- ness of these fixtures.

The survey was conducted for Public Works Canada in collaboration with Brian W. Tansley & Associates.

C]

Michael Ouellette is senior technical of- ficer with the Institute for Research in Construction, National Research Council Canada, Ottawa, Ont.

References

1. Ouellette, M.J., "In Search of the Magic Number", Lighting Magazine, Vol. 4, No. 2, pp. 22-24, April, 1990.

2. Canada Gazette, Part II, Vol. 123, No. 23, pp. 4580-4587, NOV. 8, 1989.

3. Bullen, A.A., "Emergency Light- ing - Legislation and Application",

Lighting Research & Technology, Vol

.

20, NO. 2, pp. 61 -62.

4. British Standards Institution, Emergency Lighting Part I, "Code of Practice for the Emergency Lighting of Premises Other Than Cinemas and Certain Other Specified Premises, Used for Entertainment", B.S. 5266- 1988, British Standards House, Lon- don, 1988.

5. C.I.E. Technical Committee no. 4.1

,

Guide on the Emergency Lighting of Building Interiors, Commission In-

ternationale de I'Eclairage, Report no. 49, 1981. I

6. Associate Committee on the Na- tional Fire Code, National Fire Code

of Canada 7990, National Research

Council, lnstitute for Research in Construction, Ottawa, 1990.