8 emergency lighting - university of hong kongwork6002/8 emergency lighting a.pdf · mebs6002...

UNIVERSITY OF HONG KONG Faculty of Engineering

M.Sc.(Eng) in Building Services Engineering MEBS6002 Lighting Engineering

K.F. Chan of 14 Jan., 2008 All rights reserved

REFERENCES

1) CIE Publication no. 49. Guide on the emergency lighting of building interiors. (1981)

2) CIBSE TM12. Emergency lighting. (1986)

3) TREGENZA, Peter, LOE, David. The design of lighting. E&FN Spon, London. (1998)

4) HKFSD. Code of Practice on Minimum Fire Services Installation. (1998)

5) BS5266; Part 1 : 1988

EMERGENCY LIGHTING

The purpose of emergency lighting is to provide safety for occupants of a building, in the case of

failure to normal lighting system. The failure may be due to interruption of power supply, may be

due to failure of the normal lighting system itself, or in the extreme case, due to fire.

Because of this, emergency lighting must be powered independently, which switches on

automatically when required.

According to CIE Report no. 49, there are 3 categories of emergency lighting:-

1. escape lighting,

2. safety lighting, and

3. standby lighting.




1) ESCAPE LIGHTING

Escape lighting is to enable the occupants to leave the interior safely in the event of an emergency.

If the normal building lighting fails and people are plunged into darkness there is a real possibility

of panic and accidents, which could be fatal. Under these conditions it is essential that the escape

lighting be switched on immediately. The escape lighting must provide sufficient light for people

to identify the escape route and to be able to move quickly along its route to outside, avoiding any

hazards on the way. Because the emergency lighting level is usually at a much lower illuminance

than that from the normal lighting, people take time to adapt. The escape route needs to be

relatively evenly lit. In particular, the lighting should be able

to indicate clearly and unambiguously the escape route, to enable any obstructions such as

changes of direction or level to be seen;

to ensure that all fire alarm call points, fire fighting and other safety equipment can be

quickly and clearly recognized;

to provide sufficient illumination in open area, such as open-plan offices, for occupants to

move quickly towards their designated escape route.

Illuminated direction signs are part of an escape route lighting system. These not only direct

people along the route but also identify the exits.




Escape route indication

In times of emergency the escape route or routes should be clearly indicated. In some buildings

the escape routes may lead either towards normal exits or to emergency exits, which are indicated

by means of appropriate signs. Normal exit signs should be illuminated at all times when the

building is in use and should remain so when the normal supply fails. Emergency exit signs are

required to be illuminated in times of emergency though the general practice is to illuminate them

at all times.

An exit sign partially concealed within an alcove formed by a partition wall featuring a bulletin

board. These photos were taken in a jurisdiction that permits the placement of signs to the left of

doors.

Exit sign visible in smoke-free condition can be nearly obscured in smoke. Visibility is greatly

reduced by the glare from the overhead luminaire. (Adopted from IESNA Lighting Handbook 9th Edition, Fig. 29-7 and 8)

Where direct sight of an exit is not possible, a directional sign or series of signs should be

provided which should be so placed that a person following them will be progressed towards the




nearest suitable exit, which may be either the normal exit or an emergency exit. These directional

signs should be illuminated when the corresponding exit signs are illuminated.

HKFSD stipulates that if exit sign is not installed immediately above an exit or if an exit is not

clearly visible from normally occupied parts of a premises, an internally illuminated directional

sign to BS5499: Part 1 shall be provided.

Methods used for illumination of signs may be:-

1. Lamps external to the sign;

2. Lamps contained within the sign.

It is recommended that the method of illumination described under 2 above be used within any

area where the normal lighting may be deliberately dimmed or extinguished. On no account

should the lamps within the signs be dimmed.

In the event of failure of the supply to the normal lighting, escape route signs should receive the

power needed for illumination from the emergency power supply.

Self-luminous signs to BS5499: Part 2 are approved for use in HK, however, their use is not

permitted where legislation specifies illuminated exit signs.

Visual impact and legibility of signs

Visual impact and legibility are dependent upon size, viewing distance, contrast, luminance and

positioning.

Lettering height

CIE recommends that the size of the pictograph in an exit or emergency exit sign should be at

least 300

1 of the maximum distance from which the sign is expected to be viewed.

CIBSE gives clear guidelines that sign of lettering height of 75mm should be used for viewing

distances up to 18m, and a lettering height of 125mm should be used for viewing distances more

than 18m but not exceeding 36m. For signs at viewing distances more than 36m, the lettering

height should be

( )45

9 distance viewingmaximum125 height Lettering

+×=

where the lettering height is in mm, while the viewing distance is in m.




Luminance & Contrast

The contrast between the illuminated face of a sign and the background against which a sign will

be viewed in times of emergency should be sufficient to make that sign easy to see but not so great

as to produce disability glare. The contrasts contained within the pictograph must be such as to

make its message instantly clear when illuminated during time of emergency. Effective contrast in

either case may be in brightness and/or in colour.

Minimum 15 cd/m2

Maximum 300 cd/m2

Luminance of Pictograph

Ratio 1:10

CIE

About 30 cd/m2

Minimum 2 cd/m2

Maximum 80 cd/m2

Luminance of white lettering (with filter

removed), or the translucent white surround

Variation 6:1

CIBSE

In many cases luminaires may also bear the signs used for escape route indication. The restrictions

regarding the admissible range of luminances then only refer to the illuminated face of the sign;

the underside may be brighter.

CIBSE recommends that for signs having opaque surrounds to the letters, the lettering should

preferably be green. For signs having translucent white surrounds to the letters, the lettering

should have an opaque dark green finish.

The HK FSD requires words of Exit signs shall not be less than 125mm high. Chinese

characters shall have vertical strokes minimum 15mm wide and horizontal strokes

minimum 10mm thick. Contrasting color shall be green/white, green/black, or white/green.

In order to give the signs maximum visual impact they should be placed / perpendicular / to the

line of sight of persons using the escape.




(Adopted from “Acing Emergency Lighting” by Rob Sumner, LD+A August 2005)

Escape route illumination

CIE recommends that the horizontal illuminance (E) at floor level on the centerline of any escape

route must at no point be less than 0.2 lux in order to enable occupants to avoid bumping into

obstructions. However, the higher the illuminance the more likely it is that the occupants will

move swiftly and confidently along the escape route so that in many cases a minimum of 1 lux

may be regarded as preferable. For safe movement a uniformity ratio Emax / Emin = 40 : 1 )0.025

1(

along the centerline should not be exceeded.

The escape route illumination should come on within 15 seconds after failure of the normal

supply.

CIBSE further recommends that for any part of an auditorium or stadium, having a fixed seating

layout, the average horizontal illuminance, when measured on a plane 1m above floor / pitch-line,

should not be less than 0.1 lux over any seated area, with uniformity of Emin / Eav greater than

40

1..025.0 ei

.




For any part of an auditorium or stadium where movable or stackable seating is used, the average

horizontal illuminance, when measured on an unobstructed floor, should be not less than 1.0 lux,

with a uniformity of Emin / Eav greater than 0.025

CIBSE also recommends that for any part of an auditorium or stadium, which is permanently

constructed as a series of steppings, the average horizontal illuminance when measured at the

nosing of each unobstructed step should be not less than 1.0 lux, with a uniformity of Emin / Eav

greater than 0.025.

The HK FSD requires 2/1/0.5 lux for staircase/night clubs, restaurants, dance halls/ cinemas,

theatres respectively with an activation time of emergency lighting within 5 seconds, and

emergency generator set be up in 15 seconds.

Escape lighting luminaires should be sited:

1. near each exit door

2. near each emergency exit door

3. at all point where it is necessary to emphasize the position of a potential hazard e.g.:

i. near each intersection of corridors,

ii. near each change of direction (other than on a staircase),

iii. near each staircase so that each flight of stairs receives direct light,

iv. near any other change of floor level,

v. outside each exit and emergency exit and close to it, leading to an agreed safe area.

Additional luminaires, as required, should be sited so as to ensure that the lighting throughout the

escape routes complies with the recommendations for minimum illuminance and illuminance

uniformity given above. Good illuminance uniformity is more easily achieved by using a greater

number of luminaires with lower light output than by employing a lesser number of more widely

spaced units with higher light output. The HKFSD stipulated a minimum of 2 fittings

Visibility of hazards

By itself, illuminance is not a sufficient criterion of visibility, since it refers only to the light

falling on a surface and not to the amount reflected back to the eye – a white object can be seen

with much less light than a dark one. It is recommended that all permanent potential obstructions

or hazards on an escape route be light in colour with contrasting surround. Such hazards include

the nosings of stair treads, barriers and other changes in floor level, and walls at right angles to the

direction of movement. In restricted areas, such as corridors, light-coloured decoration throughout




is advantageous, and under emergency conditions easily seen vertical surfaces can assist

considerably.

Potential hazards and obstructions on an escape route should be light in colour with contrasting

surround.

Illumination of fire alarm call points and fire fighting equipment

Fire alarm call points and fire fighting equipment provided along escape routes should be

illuminated either by emergency lighting or by normal artificial or daylighting at all times while

the building is occupied.




2) SAFETY LIGHTING

Where failure of the normal lighting could place people in danger, safety lighting is needed. This

may involve shutting down a hazardous process such as allowing the operator of a circular saw to

finish his job or a steel mill operator handling hot metal to shut down the process before they

leave. Another example is to provide emergency generator backed up explosion proof luminaires

in chemical plants or ammonia refrigeration plant rooms. Without safety lighting, further danger

could arise both to the operators and to other users of the building.

In some situations, such as hospitals, it may be necessary to provide safety lighting to allow

continuation of vital activities such as that in an operation theatre.

The illuminance on the working plane given by safety lighting should not be less than 5% of that

given on the same plane by the normal lighting, although for tasks of particular danger this should

be increased to 10%. In practice, the same luminaires are often used, powered by an alternative

supply. Safety lighting should be supplied within 0.5 second of the failure of the normal supply.

Note that although lifts usually do not form part of a designated escape route, in order to prevent

panic and enable help to be summoned, safety lighting should always be provided in lifts and

elevators.

In general, escape lighting is necessary in addition to safety lighting.




3) STANDBY LIGHTING

Standby lighting is provided in buildings where it is decided that, for reasons other than safety,

work or activities should be continued in the event of failure of the normal lighting. Examples

are shops and certain industrial activities.

Standby lighting, to enable normal activities to proceed, should be of quantity and quality of the

normal lighting, though this is entirely voluntary. Standby lighting is often provided by some or

all of the normal luminaires. It is recommended, in any case, the illuminance should be not less

than 10% of that normally recommended for the activity concerned. The interruption time in

switching from normal to standby lighting is a matter of economic consideration. In general it

should not exceed 15 seconds, although shorter interruption times may be desirable, such as for

instance, 1.5 seconds in commercial applications to prevent shoplifting. Standby lightings are

frequently powered by back up supplies as well.

Note that while escape and safety lighting are enforced by law in most countries, provision of

standby lighting is usually voluntary.

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