Switch room suppresion

[Bert]

A client is having a facility built in Moscow and is being advised by their American designers that the switch rooms, computer rooms and generator rooms should be protected with stand alone fixed dry powder units. These are ceiling mounted pressurised cylinders which contain up to 50 kgs of ABC type dry powder and which are operated via a frangible (sprinkler type) head.

The building is sprinkler protected but the designers are strongly against any form of wet system, including water mist, in association with any electrical installation.

My concern is that the extinguishers are single knock flooding systems with no safety interlock to prevent accidental discharge.  If dumped, it would take days, if not weeks to clean up and reinstate the facilities.

Obviously gaseous suppression is an option, but there is little space for the cylinders. I’ve used water mist, and triple interlocked pre-action sprinklers before, but was wondering what others opinions were on the protection of switch rooms and the like?

[Fishy]

Probably easier to clean up after a water mist discharge than DP!

Oxyreduct might be an option?

[Paul]

I have always been a big believer in using very early warning systems, in the form of an aspirating smoke detection.  There are a few types out there now, there is the older VESDA system that works on air sampling the contaminants and then there is the newer type that only looks at products of combustion.  Both are extremely effective.  I know of several blue chip companies that use this type of system, without any form of suppression.  

These systems can be set up to be extremely sensitive and provide a pre-alarm very early on.  As I say I have seen this work very well in industry, although the companies also have a fire crew covering the sites.

I can pass more info by email if you like

[Ashley Wood]

If they were to use a high pressure water mist system then it can be proven that there is no problem using it upto 35Kva. The problem with the use of any gaseous system is that the area has to be sealed up tighter than a d**** proverbial. A lot of switch rooms have cable entry points and even vented doors, so this may be a problem. DCP in a switch room would cause so much damage it is not worth the risk. The powder is corrosive and will eat into everything. After discharge the switch gear would have to be replaced to guarantee its reliability.

A VESDA type system would be ok if it can be guaranteed that no contamination from outside the room can get in. Also, if the switch gear is remote then you need to extinguish the fire rather than just tell someone that it is on fire.

The only other type of system you could use is CO2 but we all no about the hazards this can create. However, you have to consider the products that are available in the country it is destined for and some of the more 'exotic' systems may not be available and cannot be recharged after discharge.

I have seen many such rooms protected by sprinklers! especially when it is an American insurance company.

[Mr. P]

Are the US designers looking at this with any view on NFPA requireemnts?

[kurnal]

I understand it is a lack of space that precludes the use of a gaseous system. The cylinders should never be in the protected room so maybe there is space elsewhere?
Nitrogen or the more recent technology such as Tyco Wormalds Inergen ( Air with about half the oxygen taken out and replaced by more CO2 plus a bit of argon) will inhibit combustion whilst the atmosphere remains breathable. There needs to be a one way vent fitted so that if the system operates  the incoming gas does not create an over pressure in the room but other than that  doors, ducts etc can be standard.
Advantage is no mess or damage when it operates.