CO2 Fire Fighting Discharged During Lightning Storms

I assume that you have called the fire equipment supplier and your service technician ??????????

You have spoken to them or your alarm service supplier????????

What have you done???

Most likely cause sounds like a lack of a ground shield on the DC line to the initial charge. Lightning strikes can cause large transient pulses on improperly shielded wires.

Besides the incidents that happend when the room was not occupied. In case the CO2 releases because of a real fire - you still need a warning tone for everyone in it not noting there is a fire instantly. As this is an automated system there is still a chance for injury otherwise.

Sorry I can not help you with your question but if you are aiming at getting and audio alarm - you better do so!

I suspect when the designed sensors set it off, that there is an audible alarm. What he is looking for is a reason for the spurious ignition of the explosive charge. I suspect induction perhaps.

Like silverthorn mentioned i guess the lightning must have created some transient pulses which artificially caused triggering of 12 v pulse command causing CO2 to release. please check the whether Earthing strips are proper or not and whether your lightining arrestors are properly mounted to absorb the entire voltage shock being generated. Also you should find the cause as to why ur alarm signaller failed in giving response...!!

"there is no pre release alarm to warn occupants"

Your establishment violets basic safety norms. It may be even violating your local relevant fire code.

Oh I forgot to add:

There is a code requirement that a pneumatic siren be installed in conjunction with the mechanical time delay. This siren operates off of the CO2 supply. Therefore occupants will have an indication of pending discharge even if the system suffers a spurious discharge.

thanks. we will look into exchanging the explosive type with a solenoid system. The practice here is supposed to be based on NFPA but does not seem to comply with many of the code requirements you list. (e.g. mechanical time delay and pneumatic siren).

When we started work here there was even opposition from the fire services to having a mechanical lock off device to disable the CO2 system when work was taking place in the rooms.

thanks-

Good reply: it is a good post from Eugene: he noticed that something is not as foreseen and could be dangerous if not discussed and changed adequately.

I suppose he is the supplier of the material in this case.

#7,8 Wmifire is correct, basically. I had 2 such events in my life from freon flooding telecomm centers. One event scared the life out of some people.

The setup was with sensors divided into zones. One sensor in each of 2 different zones needed to trigger, essentially immediately. Then, since freon displaced most oxygen, you had 30-45 seconds to clear out.

The embarrassing thing of the bigger event was, that the floor above got a water leak. Nobody thought to inform the telecomm. The water seeped thru to the sensors, and falsely triggered 2 of them.

The electrical standards were absolutely tops. No nearby lighning was able to do damage.

So it is what you think you know, but dont, is the thing coming back to bite you on the behind, firmly.

Planning for rare event is a different science. See airline technical safety.

We had CO2 cylinders operated by solenoid without any problem. There were a local signal outside the room where system is installed as well as a siren in the main substation from which power is provided to the room.

There are several solutions to the mayor issue: the risk people got trapped in an accidental discharge event.

1. Do you really need the explosives? I only know one application where it is required to act that fast: poisenous gas protection in dismantling stations of old chemical ammunition. (I hope they don't produce them anymore, we have still sufficient of it rusting away since WW1) In this application it was necessary to create a water curtain within millisecond from the detection of a detonation, it worked with explosive assisted deluge valves, water filled lines with rupture disks, ...

As you anyhow have to wait the necessary time to evacuate the room, the delay introduced by a solenoid can't be the time critical problem.

2. Is it really required to work with CO₂? Other non lethal and non potential environmentally damaging alternatives are available (eg Inergen)

My 5c on the potential reason for discharge: in your application could it be that the outside earthing is somehow influencing the inside earthing of the building?

Normally you should earth and short the two wires to the explosive when not required to discharge.

Imagine that there is a potential that the shell of the explosives is differently earthed than the leads, lighting strikes and creates a differential between the two, boom.

one of the reasons may be the piping connected to the steel of the building, the leads connected to the "clean" intrument earthing as this was certainly not affected by any outside influence.

Thanks.

Your point about the different earths. The shell of the explosive will be in contact with the metal of the cylinder valve which is in contact with the ground and other metal pipe work all connected to the LVAC earth. While the electrical connection to the explosive is from the DC source (rectified AC) which is not earthed. A near by lightning strike could result in a voltage difference.

CO2 is not our preference for the FF systems. However for historical reason we have many CO2 FF installations. It would require total redesign and significant expense to replace them all. However there is a clear need to make them safer.

I have learned a lot from this query and the responses. Thanks to everyone who took the time to respond.

Yes and No, emphatically.

When earthing in a distributed system, that the firefighting system need to be, earth here is not earth everywhere. As lightning occurs, the current from the strike point spreads out, setting up differential voltages, that are destructive.

Shielding is the first layer of protection.

Shielding of a cable is second.

Double shielding of a cable is third.

Independent factor is getting away from the microseconds triggering of the shotgun primer trigger mechanism. Enlarging the trigger time lowers the sensitivity by the same factor.

I bet, most of the factors are ignored.

Earthing starts easy but in the end is one of the most difficult parts in electrical engineering.

Certainly when you start tossing around with detonators and short time events like lightning.

Fortunately the switchgear rooms were unoccupied and no injury to personnel resulted.

Fortunate indeed. Please see: http://en.wikipedia.org/wiki/Carbon_dioxide

A review of CO₂ systems identified 51 incidents between 1975 and the date of the report, causing 72 deaths and 145 injuries.^[22]

Most likely, the tripping pulse did not originate with a direct strike, but was the result of an EMF pulse in the atmosphere. Not long ago, I lost a motherboard to just such a phenomenon- the strike destroyed a tree about 20 meters from the building housing the computer, and did not enter the building via the electrical grid- no other damage, no damage to anyone else in the neighborhood (except for the neighbor who happened to be parked under the tree at the time).

Some time back, in an attempt to understand non-typical lightning damage, I did extensive literature research to try and figure out what was going on. We were losing specific transformers on a distribution grid (actually, two such isolated grids with the same issue), with no effect on identical transformers on the same grid. No evidence of direct lightning strike any where in the vicinity, which is what most lightening protection systems (lightning rods, surge suppressors, etc.) are designed to protect against. One of two causes were identified- either we were getting EMF through the atmosphere, or we were experiencing reverse-polarity lightning (occurring typically at the tail end of a storm).

Whatever the actual cause, adding Faraday shields seems to have significantly reduced the frequency of incidents...

I'm a bit late, but I have a story:

Our CO2 system protects a gas turbine enclosure, is actuated by solenoid and set to automatic operation.

Maintenance tech's opened the enclosure door for an investigation when lightning struck, discharging the CO2. No spurious earth problems or strange currents here. Concensus is that the flame detector (UV type) appears to have 'seen' the lightning and activated the system discharge. Naturally, no proof on offer, but I can live easy with this rationale. The obvious is sometimes overlooked....ring any bells ?