Emergency Evacuation Lighting in Buildings
Editor's note: This is one in a historical series of documents published in our Lab Notes series around the turn of the century. The series is a snapshot of current understanding at that time, we hope that you find it interesting.
In the early 1970s there had been a number of serious fires in commercial buildings which resulted in significant loss of life as well as of property. These occurred mainly in Europe, the most infamous here in Australia occurred at the Whiskey Au Go Go night club in Brisbane on March 8th 1973.
In almost every case it was established after investigations, that the main cause of death was either by people being trampled underfoot while trying to escape, or by the effects of smoke inhalation as they tried in vain to find the exits from the buildings.
In almost every case it was established after investigations, that the main cause of death was either by people being trampled underfoot while trying to escape, or by the effects of smoke inhalation as they tried in vain to find the exits from the buildings.
The LG/7 committee
In 1976 Standards Australia ( then SAA ) formed a committee known as LG/7 which was formed to examine the possibility of developing an Australian Code of Practice for Evacuation Lighting. The role of this committee was to develop means by which people could escape from any building under threat from fire. It was not intended to directly assist firemen or rescue workers, nor to allow work processes to continue, even on a limited basis. The Foreword of AS2293 spells out quite clearly the difference between Standby, Safety, and Evacuation Lighting.
Initially LG/7 had three working groups: to investigate the proposed lighting, to investigate the electrical aspects, especiaIIy battery types and to determine how and where the new Standard was to be applied. The third group was made up from local government representatives from each State, and was soon disbanded as it became impossible to gain agreement between the States on the legal standing of such a Code.Working Group 1 first considered the fundamental questions of how much light would be needed to safely evacuate people from a building, and how the system would be assessed for compliance. A solution to the latter question was required to address assessment both in the design stage, and when the project was completed.
Initially LG/7 had three working groups: to investigate the proposed lighting, to investigate the electrical aspects, especiaIIy battery types and to determine how and where the new Standard was to be applied. The third group was made up from local government representatives from each State, and was soon disbanded as it became impossible to gain agreement between the States on the legal standing of such a Code.Working Group 1 first considered the fundamental questions of how much light would be needed to safely evacuate people from a building, and how the system would be assessed for compliance. A solution to the latter question was required to address assessment both in the design stage, and when the project was completed.
Putting numbers to the problem
In the late 1970s, there were three major international proposals which had been adopted, or were about to be adopted, in various countries. The British had a recommended minimum level of 0.2 lux, the American proposal had an average of one foot candle, ( approximately 10 lux ), and the Russians required one tenth of the normal average illuminance. ie. If the room average was 400 lux, then the average emergency lighting required would be 40 lux. The three different requirements meant not only a wide variation in illuminance values, but a wide difference in the costs of the emergency lighting installations and battery capacities.
Perhaps it is not too hard to imagine that the 0.2 lux proposition was the most attractive for the Australian committee to consider, BUT, it was realised that it would be very difficult to measure with accuracy, or to design a 0.2 lux system. It was further realised that perhaps a person could not visually adapt to such a wide change of lighting levels from 400 lux in a typical office to 0.2 lux level in just an instant. The committee was concerned that this visual adaptation would induce panic. Another matter of concern was how people would react in those few seconds after being suddenly plunged into darkness. How would they feel, and how would they respond both as individuals and as a group?
To test these questions, a number of trials were carried out in Melbourne with the co-operation of a group of members of the Illuminating Engineering Society as participants and observers. These people came from a wide variety of ages and experience. The results of these experiments can be summarised as follows :
The Committee was impressed with the experimental work done at the Jules Thorn Lighting Laboratory in the United Kingdom. The conclusions which they reached were that 0.28 lux was a safe minimum illuminance , and that a variation in illuminance along an escape route approaching 50 :1 had no effect on the ability to see.
It was found that the onset of panic within a crowd situation was caused by a number of factors which included: loss of orientation, a feeling of isolation, even though surrounded by a crowd of people and an awareness that mere seconds in time seemed interminable. These effects are heightened if there is a presence or even the smell of smoke, and it can be easily understood that the first question to enter a person's mind is “How do I get out of here ?"
Working Group 1 struggled with the problem of the presence of smoke and how to compensate for it, or alternatively how to quantify the level or density of smoke. In the end it was left to a comment in the Foreword of the Standard which states:
“It is recognised that the presence of smoke will have a detrimental effect on the visual conditions provided by emergency lighting. The Committee is of the view that there is no practical way of ensuring that the lighting system will continue to be effective under smoke conditions, and that dependence must be placed on other measures such as in the building construction and ventilation, to keep the escape paths as free as possible from smoke."
It was realised in the very early deliberations of Working Group 1 that there was a need to check the design for compliance in both the planning stage and after the project was finally completed. It was also appreciated that the primary group of people doing the checking would be the Building Surveyors and Inspectors who have little or no lighting knowledge. This led to the creation of the Tables of Maximum Spacing for a given mounting height and given luminaire classification. In the 1995 edition of AS/NZS 2293 illuminance calculations by either a computer aided design program or conventional point by point calculations are permissible.
Perhaps it is not too hard to imagine that the 0.2 lux proposition was the most attractive for the Australian committee to consider, BUT, it was realised that it would be very difficult to measure with accuracy, or to design a 0.2 lux system. It was further realised that perhaps a person could not visually adapt to such a wide change of lighting levels from 400 lux in a typical office to 0.2 lux level in just an instant. The committee was concerned that this visual adaptation would induce panic. Another matter of concern was how people would react in those few seconds after being suddenly plunged into darkness. How would they feel, and how would they respond both as individuals and as a group?
To test these questions, a number of trials were carried out in Melbourne with the co-operation of a group of members of the Illuminating Engineering Society as participants and observers. These people came from a wide variety of ages and experience. The results of these experiments can be summarised as follows :
- People of all ages could adapt from 400 lux to 0.2 lux levels in a few seconds without undue difficulty.
- It is important that vertical surfaces such as walls and doors be recognisable to assist in orientation.
- Emergency lighting must be integrated with Exit signs, and there must be a direct line of sight to either the actual Exit sign or to directional signs pointing to the Exit signs.
- Using conventional measuring instruments, it is almost impossible to accurately measure illuminance values in the order of one lux or less.
- It is important that the emergency lighting is activated within 1 second of the failure of the mains power lighting, and to at least 50% capacity within 5 seconds.
The Committee was impressed with the experimental work done at the Jules Thorn Lighting Laboratory in the United Kingdom. The conclusions which they reached were that 0.28 lux was a safe minimum illuminance , and that a variation in illuminance along an escape route approaching 50 :1 had no effect on the ability to see.
It was found that the onset of panic within a crowd situation was caused by a number of factors which included: loss of orientation, a feeling of isolation, even though surrounded by a crowd of people and an awareness that mere seconds in time seemed interminable. These effects are heightened if there is a presence or even the smell of smoke, and it can be easily understood that the first question to enter a person's mind is “How do I get out of here ?"
Working Group 1 struggled with the problem of the presence of smoke and how to compensate for it, or alternatively how to quantify the level or density of smoke. In the end it was left to a comment in the Foreword of the Standard which states:
“It is recognised that the presence of smoke will have a detrimental effect on the visual conditions provided by emergency lighting. The Committee is of the view that there is no practical way of ensuring that the lighting system will continue to be effective under smoke conditions, and that dependence must be placed on other measures such as in the building construction and ventilation, to keep the escape paths as free as possible from smoke."
It was realised in the very early deliberations of Working Group 1 that there was a need to check the design for compliance in both the planning stage and after the project was finally completed. It was also appreciated that the primary group of people doing the checking would be the Building Surveyors and Inspectors who have little or no lighting knowledge. This led to the creation of the Tables of Maximum Spacing for a given mounting height and given luminaire classification. In the 1995 edition of AS/NZS 2293 illuminance calculations by either a computer aided design program or conventional point by point calculations are permissible.
As a general rule, lighting installations which consist solely of recessed batwing luminaires tend to be very boring, and produce dull and gloomy interiors. However, if an uplighting installation is added to the design the whole visual environment changes, and offices can become very pleasant workplaces.
Because of the lightened ceiling the Glare Index value will also be reduced, and using a PC and the formula based method, the revised GI value can be calculated. However, it is troubling to note, that neither the Tabular nor the Luminance Limiting methods can calculate a glare rating for this type of installation.
Because of the lightened ceiling the Glare Index value will also be reduced, and using a PC and the formula based method, the revised GI value can be calculated. However, it is troubling to note, that neither the Tabular nor the Luminance Limiting methods can calculate a glare rating for this type of installation.
Classifying emergency luminaires
Fig 1: Classification curves
|
Appendix C of AS/NZS 2293.3 explains the classification of emergency luminaires using an alpha-numeric system. The alphabetic component is in the form of the letters A, B, C, D or E, and these define the general shape of the Intensity Distribution Curve. The shape is considered in both the C0 and C90 planes. Figure 1 illustrates these generalised Intensity Distribution Curves.
The Standard includes a set of formulae by which the luminous intensity (lp) at any particular angle may be calculated, relative to the assigned luminous intensity (Io) in the downwards vertical direction. The formulae for the luminaire classes are listed in Table 1 below. |
The formula for each classification calculates the minimum intensity at a given gamma angle. lp is the luminous intensity emitted at the gamma angle, expressed in terms of Io. Io is the luminous intensity in the downward vertical direction, assigned in accordance with section C of the standard.
The numerical component of the classification are based on the R10 series of preferred numbers (1.0, 1.25, 1.6, 2.0, 2.5, 3.2, 4.0, 5.0, 6.3, 8.0). The actual number which relates to the downward vertical Intensity value is an assigned number. This number must be equal to or less than the actual luminous Intensity in the downward vertical direction. For example a classification of D63 means the distribution of the luminaire satisfies the Classification D equation with Io = 63 cd.
The numerical component of the classification are based on the R10 series of preferred numbers (1.0, 1.25, 1.6, 2.0, 2.5, 3.2, 4.0, 5.0, 6.3, 8.0). The actual number which relates to the downward vertical Intensity value is an assigned number. This number must be equal to or less than the actual luminous Intensity in the downward vertical direction. For example a classification of D63 means the distribution of the luminaire satisfies the Classification D equation with Io = 63 cd.
| Classification | Formula | Range |
|---|---|---|
| A | Ip = I0 cos4(γ) | γ ≤ 70° |
| B | Ip = I0 cos3(γ) | γ ≤ 70° |
| C | Ip = I0 cos1.5(γ) | γ ≤ 70° |
| D | Ip = I0 (2 + cos(γ))/3 | γ ≤ 70° |
| E | Ip = I0 (1 + [0.04 γ / 30]) Ip = 1.07 I0 cos(2.6 (γ - 35)) |
γ ≤ 30° 30° ≤ γ ≤ 65° |
Table 1: Classification formulae
An example classification
To illustrate the classification method and the result of the assignment process, consider the following example. The actual measured intensity values in the C0 and C90 directions are listed in Table 2. If we assume a mounting height of 2.7 m, the spacings for the assigned classifications are per Table 3.
| Gamma angle (deg) | C0 intensity (cd) | C90 intensity (cd) |
|---|---|---|
| 0 | 128 | 128 |
| 10 | 126 | 125 |
| 20 | 115 | 118 |
| 30 | 86 | 107 |
| 40 | 54 | 90 |
| 50 | 27 | 49 |
| 60 | 9 | 15 |
| 70 | 4 | 6 |
| 80 | 2 | 4 |
| 90 | 0 | 0 |
Table 2: Example luminous intensity distribution
Table 3 shows that even though with an I0 value of 128 cd, the shape of the C0 curve is such that it can only be assigned a D5 classification (based on I0 = 5 cd), yielding a maximum spacing of 8.1 m. The best (highest) maximum spacing in the C0 direction is for the E classification, being E20 and yielding a maximum spacing of 10.4 m. Likewise, in the C90 direction, the best maximum spacing is 11.2 m by assigning an E32 classification. The luminaire is thus assigned a classification C0 = E20, C90 = E32.
| C0 classification | C0 spacing (m) | C90 classification | C90 spacing (m) |
|---|---|---|---|
| A125 | 9.9 | A125 | 9.9 |
| B63 | 10.0 | B100 | 11.0 |
| C16 | 9.3 | D6.3 | 9.0 |
| D5 | 8.1 | D6.3 | 9.0 |
| E20 | 10.4 | E32 | 11.2 |
Table 3: C0 & C90 assigned classifications
