CO2 suppression systems

[Guest]

Anyone any thoughts/evidence on the effect of a CO2 suppression system on a fire in a high voltage switchroom/substation?  Rumour is that electricity suppliers doubt whether they would do any good and would now not instal them due to the H&S implications and maintenance cost.

[JamesG]

If you can hold the concentration in the room they should put the fire out.  There are issues with openings in rooms especially if the rooms have ventilation louvers on the doors, as electrical rooms often seem to have.  Design should be in accordance with the British standard (I think the concentration rate for the CO2 would have to be based on deep seated fires for switchrooms, which I think is 60%.  Also, you may need extended discharge to cope with any losses as you have to maintain concentration for 20 mins – please check the figures quoted as they are off the top of my head)

The issue regarding H&S would depend on whether the room is unmanned and the facilities the system has to prevent operation when occupied.  I’ve seen the provisions range from procedural to using castel key interlocks to prevent the doors being opened unless the CO2 system is physically isolated.

I have seen them designed for swichrooms previously - though they were older oil filled switch gear if I remember correctly.

As for proof, the manufacturers would be able to show you videos of fires being put out, but they may not really count as proof.  Alternatively, the appendices of NFPA 12 (co2 systems) or 850 (electric generating plants) may have examples of where the systems have worked.

If I come across anything else, I will email you, if you give me your email address.

Regards

James Goodstadt

[AnthonyB]

They were certainly common installations up to the 80's with the Kidde Graviner CO2 warning token a familiar sight on the older oil transformer substations, generally where they were inside other buildings rather than in their own seperate building.

I believe there have been a few fatalities in these areas over the decades, and I've also noticed a trend that the systems have not been fitted in new or renovated subs for some time now.

A common concern when we find subs in buildings with CO2 tokens that we are FRAing is whether the system is ever maintained, that there is no link to the buildings fire alarm and that there are no interlocks.

On a couple of our site the subs and distribution rooms have CO2 systems with very rudimentary (but effective) safety interlocks - they have been retained whilst present, but supplemented by AFD. The costs of proper maintenance are high, especially when the installation comes up to a 10 year interval and you have two banks of 12 33.6KG CO2 cylinders to betaken away and overhauled. We find that Smoke AFD satisfies life saefty needs and CO2 systems are only retained where insurers request it.

On one site, a shopping centre, the Halon 1301 system to the subs was removed and Smoke AFD substituted instead - a common finding now is that standalone extinguishing systems are replaced with AFD on the host premises fire alarm system.

[colin todd]

A problem is that the CO2 will leak out all over the shop, and you will end up with dangerous concentrations in places you dont expect. It should probably be avoided inside just about any building. its ok if the sub is a free standing building.

[Brian Catton]

I agree that Co2 would have limited value in a substation.
Most subs are full of sealed transformers and switches. In my experience the problem comes from within the equipment itself or sometimes a badly made cable joint.
The former sometimes results in an explosion due to vaporisation of the coolant.
The best solution is to use the existing telemetry to detect faults, combined with smoke detection. The control room operators can then take the necessary speedy action to isolate the affected Sub station.

[Ken Taylor]

What is the issue about not taking the inert gas option for these installations and going for AFD upon removal of the halon?

[Chris Houston]

Presumably the point of the fire supression is that it should put the fire out, thus limiting damage and business interuption times.  This limits the cost of the loss and may be an insurance requirement.

AFD generally does nothing but send a signal to an alarm centre who phone the fire brigade who (depending on their policy) respond to it and then start tacking the fire.  

These are two very difference scenarios.  The first one is likely to mitigate the business interuption and material damage losses better.

[AnthonyB]

Hence why the only objection we have had to the removal or non installation of these systems is on one site where the insurance wanted it kept.

From a life safety point of view AFD to ensure the nearby areas were promptly evacuated was accepted by all parties, it was only property protection that required the CO2 (that incidentally was set for manual or fusible link release, not by smoke)