Its been a while since The Light Review paid attention to what’s happening in emergency lighting design and application. So when Richard Hayes got in touch to suggest that the timing was good for a bit of a review – and a chance for a bit of finger-wagging – how could we resist. This is what Richard had to say to us:
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BS EN 1838:2024 and BS EN 50172:2024 are the two standards that are most relevant to emergency lighting. Both were updated and re-issued in 2024. There are many changes in both documents, both in terms of emphasis and approach and changes to detail technical requirements. I’d like to focus on those that present potential difficulties to everyone concerned in the application of emergency lighting standards.
The biggest and probably most controversial change is the added requirement in BS EN 50172:2024 Clause7.3 which calls for initial verification of “photometric requirements according to EN1838” and references Annex B as the test method. Also, Clause 7 .4.5 calls for verification every 5 years “illuminance measurements shall be performed once every five years in order to verify the corresponding luminous requirements according to EN 1838.” This again references measurements according to Annex B. Annex B is also reproduced in whole in EN 1838:2024
Annex B starts by listing all of the things that could affect an onsite measurement of emergency lighting. It states that a complete assessment of an emergency escape system seems overly demanding in terms of time and goes on to state that calculation can be used to reduce the number of measurement points. But it says this can only be done if a correlation has been established between physical measurement and calculation. Some guidance within the document as to how many measurements would be deemed “enough” to make a correlation would be useful.
Later on in Annex B. 5.2 a measurement grid is offered that is the same as the calculation grids in EN 12464 so there is a strong implication that a full grid should be measured. But before any testing can be carried out, Clause B 5.2.1 states “All movable furniture and obstacles that cast shadows on the measurement grid should be removed for the measurement.” There is no suggestion as to how this might be achieved in a commercial or industrial setting.
Possible test methods
Annex B 4.1 gives four possible test methods, which are expanded in following paragraphs B.4.2, 3 4 and 5.
There are recommendations for the number of illuminance meters needed, the number of measurements to take and what corrections to apply for each method, depending on how variable or constant are either the stray light or the emergency light fixture.
| Method | Stray light | Emergency Light |
| A | Constant | Constant |
| B | Constant | Variable |
| C | Variable | Constant |
| D | Variable | Variable |
The commentary considers that a constant current drive to LEDs will give a constant emergency light output. In my world either the LEDs are maintained so they start hot and cool when switched to emergency or non-maintained so that they start cool and will then warm as power is applied on mains fail. In either case there WILL be a period after switch-over when THINGS WILL NOT BE CONSTANT. At best, you might be able to consider a constant current luminaire as stable after an initial period of variation. Given that the speed of evacuation from a building may preclude any such stabilisation, this feels like an important omission in the calculation methodology.
Method B relies on constant stray light, so may just be possible with good blackout conditions, and a moonless night in a rural location, I believe this would be virtually impossible in any built-up location.
Method D would be used for most locations. Method D requires two illuminance meters capable of resolving to 0.01 Lux. At each point, measurements are required firstly with straylight and the emergency lighting OFF, then another measurement with emergency lighting ON. Then apply a correction for variation across the duration. In my opinion this would be impossible in three hours yet alone for a one-hour duration system.
Initial testing will probably be the responsibility of the installation contractor; five-year verification requirement will be the responsibility of the Responsible Person under the 2005 Regulatory Reform Order. The Responsible Person is generally the person who has control of the premises and is responsible for fire safety measures. This could be the employer in a workplace, or the building owner or manager in other situations.
Meanwhile, in the real world
For a long time I was a school governor – part of a Multi Academy Trust. I would love to be in a meeting with a MAT facilities manager to tell them that once every 5 five years they have to strip each type of classroom, black it out to prevent stray light, hire two expensive illuminance meters, and then spend probably a couple of nights making measurements, or to find the budget to pay a contractor to do the job. There is very little budget in schools for books and teachers and there is no money for this (possibly contractually-required) action! I assume that, at present, no public buildings have money to burn. If this is forced on the private sector then business costs, will have to rise.
A note on what ‘contractually required’ may mean: adhering to a Standard is not usually a legal requirement. The Regulatory Reform (Fire Safety) Order 2005 does not mention any Standards but you could be contractually bound to adhere to it by your client. Besides which I, for one, wouldn’t want to find myself in front of a prosecuting barrister trying to explain why my decision to ignore an approved safety standard had apparently led to injuries and, perhaps, fatalities.
When and how are we ever going to black-out and shut Heathrow Terminal 5 or Birmingham New Street Station long enough to make these measurements? Will these requirements ever be adhered to in the real world?
So the intent is good but in my view totally impractical. But not to accused of criticism without alternative suggestions I propose that :-
Modern lighting design programs can provide accurate predictions of illuminance in a space; building modelling using current BIM systems can be accurate. But the kicker in all of this is the accuracy of the photometric data used in the calculation. I speak from experience when I say that the quality of photometric data supplied for emergency light is at best variable in quality and at worst fraudulent. So rather than put a massive financial hit on the end-user why not legislate so that only verified photometric data can be used in emergency lighting calculations. Post-Brexit, the UK has the power to insist that products used in safety system meet stringent criteria.
We need
- A register of approved Equipment
- Emergency luminaires should be third-party tested for photometric and electrical performance.
- Manufacturers should be subject to stringent quality controls and inspections.
- Qualified lighting design software needs to be mandatory, with calculations only being acceptable when produced with approved software – by competent designers.
This would have the effect of strengthening the UK market for UK manufacturers, many of which would have nothing to fear from such a system. It would be a barrier to cheap foreign imports, no bad thing for a safety system
Applying the ATEX model
Much equipment in the construction industry has requirements for certification. If you need a model in lighting, look to ATEX certification for Hazardous area equipment. The ATEX system was brought in as direct result of industry failings resulting in the Piper Alpha rig disaster.
Surely, we owe the people of Grenfell United a similar response?
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There are other changes to BS EN 1838 and BS EN 50172 in the 2024 editions that might present a “trip hazard” to practitioners.
Under table 1, the wording for Specific Forms of Emergency Lighting says:-
Emergency lighting can be provided by maintained luminaires and maintained safety signs when the normal lighting is available. Maintained luminaires and maintained exit and safety signs shall operate when the normal lighting is required but fails.
This seems to imply that only Maintained lighting is now considered. But in Definitions both Maintained and Non Maintained safety signs are included. This wording seems unnecessarily confusing.
Using manufacturers’ available data
Emergency escape lighting design has to be based on worst conditions (e.g. minimum light output, maximum glare limits and an appropriate maintenance factor) of the luminaires during operating life and shall be based only on direct light from luminaires. Lighting calculations shall be based on the rated emergency intensities data related to the practical emergency light source flux according to EN 60598-2-22. This is not changed in the latest edition of the standards, but it is worth emphasising that emergency lighting calculations need two lumen output figures from the manufacturer, both the minimum or Practical Emergency Lamp Flux (PELF) as described above for illuminance determination and a maximum figure for the assessment of Glare under worst case conditions. A Maintenance Factor to ISO/CIE TS 22012 is also to be included in the calculation of Emergency lighting.
Escape route lighting design
Section 5.1 Escape Route Lighting states that the whole area of the escape route (with some exclusions – see below) must now achieve 1 Lux minimum. Calculations for escape routes wider than 2m can exclude 0.5m of the perimeter of the escape route. Escape routes of 2m and narrower exclude borders of 0.25 of the escape route width.
The word perimeter for wider routes is clear, and assumes 0.5 m at both edges and ends of the escape route are excluded.
Border is less clear. Dictionary definitions are mainly concerned with edges, so this could be taken as only excluding the long sides of the escape route. In the 2013 edition the centre line was used as the calculation reference, with no other exclusion; i.e. the whole length, was lit to 1 Lux with half of the width of the escape route no less than half of the centre line. It implied no exclusion at the ends.
The 2024 edition calls for more light on the escape route but there is some possible confusion as to the area under consideration. Its worth reminding ourselves that the ends of a corridor are often the places where we find exit doors – the aiming points for people making their way out of the building.
There are also a series of notes on System Integrity requirements in escape routes
Open Area design
Section 5.2 Open Area (anti-panic) Lighting is largely unchanged but now calls for coverage of non-defined escape routes that pass through an open area. The requirement is to light the shortest obvious route through the area as an escape route. Otherwise the area is to be lit to 0.5 Lux minimum excluding 0.5m perimeter of the area.
The 0.5 m perimeter exclusion is unchanged from the 2013 edition. At the time the 0.5m exclusion also applied to area task lighting as defined in BS EN 12464 part 1. BS EN 12464 part 1 was amended in 2021 and the perimeter exclusion was changed in small areas to be 15% of the width of the small area. With the 0.5m exclusion small areas e.g 1.2 m x 1.2m would only be calculated over a 200mm square in the middle of the room. The 2021 amendment to EN12464 fixed this anomaly, it feels like a missed opportunity not to coordinate standards to bring the 15% rule into open area emergency lighting.
There are no System Integrity notes for Open areas.
Toilets and changing rooms
Toilet lobbies are to be lit as escape routes. Shower cubicles and single occupancy toilets with baby changing facilities require 1 Lux minimum at floor level and 1 Lux minimum on the changing area.
There are notes on system integrity within Toilets and changing rooms.
Public Indoor Swimming Pools
The new standards call for 5 Lux horizontal on the water surface and at floor level on circulation routes, though it is not specified whether this should be an average or a minimum design figure. Surely a swimming pool and the pool surround circulation zones are the very definition of a High-Risk Task Area? In defining the pool surround as a circulation area, normal task lighting to EN 12464 would be 100 Lux, and that would, in turn, call for High-Risk Task Area lighting to be 15 Lux minimum average. EN12464 calls for 300 Lux average on school swimming pools so High-Risk Task Area lighting would be 45 Lux minimum average. Requiring a blanket 5 Lux seems like a backward step, especially given the sensitivity around Health and Safety operations..
Safety Signs
Internally illuminated safety signs are required to have a minimum luminance of 2cd/m2 , but there has been a long-standing lack of coordination here. BS EN 60598-2-22, which is the construction standard for emergency luminaires requires all emergency luminaires to comply with ISO 30061. ISO 30061. That standard requires that “in the event of smoke being of importance” all internally illuminated safety signs should meet a minimum of 10cd/m2 luminance. Are we to assume that manufacturers are providing emergency safety signs specifically for environments where the presence of smoke is NOT important?
Standby lighting
In BS EN 1838 2013, standby lighting was defined to provide the normal task lighting required under mains conditions to be maintained during mains failure. There was a proviso that a lower level could be provided to “safely terminate” processes. This reduced illuminance could be specified in the Risk Assessment. BS EN 1838 2024 now divides this into 2 definitions:
Standby lighting is a lighting system to provide sufficient illumination for normal activities to be conducted in the event of a failure of the normal lighting supply.
New Emergency Lighting Category: Local Area lighting:
The objective of Local Area lighting is to ensure the safety of people who are allowed to stay temporarily in a premise. The maintained illuminance is to be based on a risk assessment, but needs to be at least that required for emergency escape lighting as given in Paras 5.1 or 5.2. This local area lighting may be part of the overall emergency escape lighting strategy. If it is a component part of the emergency escape lighting then it should be calculated as direct illumination only, with some first reflection. It feels like Local Area lighting is exactly the same as the proviso previously included in standby lighting.
System Integrity
Previously the requirements for System Integrity were included in BS EN 50172 2004. This called for at least two luminaires in any escape route compartment and in each open area.
In BS EN 50172:2024 there is no mention of system integrity. BS EN 1838 2024 now contains references to system integrity but only for Escape routes and specific areas, Toilets and Changing rooms. There is now no requirement for a minimum of two luminaires to supply emergency lighting in open areas.
In Escape routes and for Toilets and Changing rooms emergency lighting must be provided from a minimum of two luminaires but now one of these can be an internally-illuminated safety sign. This is a departure from the previous methodology.