Emergency lighting and back-up generators

[saddlers]

Has anyone got any experience of emergency lighting and power back-up generators. My thoughts were that the generator was provided to ensure that "day to day" operational lighting would remain functional in the event of power failure (due to loss of supply, fire etc), but could not be used an alternative to emergency lighting, due to the potential for the integrity of local circuits to be affected and the initial delay in the activation of the generator. I am struggling to find any definitive guidance, can someone point me in the right direction please.

Thanks in advance!!

Saddlers

[CivvyFSO]

BS5266.1. 2005

7.2 Failure of normal supply to part of a premises
Operation of emergency escape lighting in the event of failure of part of the normal lighting supply is specified in BS EN 50172:2004/BS 5266-8:2004, 5.2.

From a legislative point of view, you need to supply lighting that will enable people to evacuate the building in the event of a fire taking out the lighting system or part of it. As you seem to be aware, a fire would only need to burn through a common supply wire to make any system reliant on a backup generator inneffective, hence the general need for batteries in the lighting units. The system you seem to be talking about is 'standby lighting' whereas what is needed is 'emergency escape lighting'.

Also, Section 5 of the new guides covers emergency escape lighting.

[Colin Newman]

I'm not sure of the context for your question, but it is common practice and indeed permissible under current HTM 81 guidance for the emergency lighting powered by stand-by generator to be used for escape purposes in hospitals.  There is an exception in this guidance though, that requires battery powered emergency lighting units wherever a delay of upto 15 seconds before the lighting circuit is restored would prove unacceptable, such as in stairways.

Having said that, there has been considerable debate over such provisions with an argument that if a local circuit is affected by a power loss but the remainder of the site remains in tact, the stand-by generator probably won't be activated unless it is dedicated to that specific part of the building.  Such an arrangement is unlikely since even the critical units such as operating theatres and ITU are usually provided with battery backed UPS.