Fire Protection


For quite a while now I’ve had 2U at the top of the rack consumed by an APW Fire Protection Unit. This clever bit of kit, found by chance on eBay for £15, will extinguish a fire using FM200 gas (with some nitrogen thrown in) when detected by either of it’s two optical smoke detectors.


Until today it hasn’t been plugged in for more than half a second because the alarm appears to be broken inside (or I need to do some sort of configuration which isn’t possible without a manual) and so it was far too noisy to use. The alarm is deafening and certainly does it’s job, but is obviously a little eager to make itself known. Just in case this was an indication that the gas might be released I disconnected the fillament in glass stopper on the end of the canister (later reconnected when I was happy it’s only the alarm that is broken).
To solve the alarm problem I have been forced to snip one of the wires to the sounder so that I can use it. This shouldn’t affect the operation of the unit, though it wont be able to give any audible indication of a fire. There is a visual indicator on the front to back it up. To replace to the audible function I will install a standard household smoke alarm.


I’m just waiting for a backup to complete before I hand over power management to it. In the event of a fire, it will instantly cut power to anything that it feeds, which in this case will be most things that are connected to the UPS. Unfortunately the UPS shutdown functionality isn’t compatible with my UPS since it uses basic status signalling, so if a fire does break out it had best not be in the UPS.

10 thoughts on “Fire Protection”

  1. Hmmmm.

    FM200 works through oxygen deprivation – it smothers the fire. Might want to make sure you have enough ventilation in that room to clear away the FM200 in a couple of minutes, or it’s not the toxicity you will be worried about!!!

  2. Thanks for the warning, although my research at the time of buying indicated that FM200 doesn’t work by oxygen deprevation and is therefore safe to use where people are present. Apparently it’s used as the propellant in asthma inhalers.

  3. Hi!

    Just found your site via and to my surprise you have the same FPU as me! I also bought mine on eBay a while back (at least a couple of years)…

    As far as FM200 goes, it works quite cleverly… The reason it has to be in the top 2U of space is because it releases and forms a layer of gas which is heavier than air. This works its way down the rack (assuming it can’t escape) and blankets any fire it may find on its way down (thus starving the fire of oxygen). Well, that’s the theory anyway!

    I’ve never had the misfortune of being in a situation where mine has gone off, but the siren is loud enough to wake the dead! This happens even if you pull mains power and leave it to run on its inbuilt battery (it ‘bips’ every 30 seconds or so).

    Nice piece of kit, never got a manual with mine, but the lights are green and the FM200 canister is ok so I know I can sleep a little bit safer at night!

    And you’re right – it is non-toxic. It was designed to replace systems that used Halon gas. Its also more environmentally friendly as a side note!

    Congrats with the ZDnet competition!


  4. Very interesting project.
    I am into home automation and slowly trying to do what your doing.
    If you need any help etc with PC hardware then I may be able to help there.
    Do you offer help and advise in what your doing, if so please email me.


  5. Hi Matt. Wow, it’s a miracle I’ve found someone else! These bits of kit seem quite rare since I think the company that originally manufactured them went bust (as far as I can tell).

    I could really do with an instruction manual to figure out why the alarm in mine goes off constantly – I would prefer to have a working alarm than a disconnected one since I don’t want to be asleep when it goes off, whether it is harmful or not.

    I guess it could be a symptom of a low battery, so since its had a while to charge maybe I’ll take it out of the rack and see if the 15v across the siren terminals is still there.

  6. Thanks Dave. What have you done so far with your projects?

    I’m ok on the computer hardware front for now – been programming and building computers for many years.

    I can offer my ideas and help to anyone who asks. I will look into setting up a contact form on this site so that contacting me is a little easier.

  7. Hi, i know this post is old, but those smoke detectors look like apollo S65’s (or S60’s depending on age)
    they are the most common type of fire detector in the UK and have a remote LED output (so if a detector is in a roof void or something, the activation status can be remotely displayed)
    if you twist the detector off its base (you may have to put a small allen key in the small hole and unscrew the locking screw) and connect a relay to the remote LED terminal, you could connect an external sounder to the device.
    find datasheets and installation instructions here:

    PS, recently found your site when looking for info on my VAMS 0808 switcher to make an AV room link system, your site is proving to be very useful and educational 🙂

  8. Thanks Luke, and I’m glad you’re finding the info here useful 🙂 Unfortunately the rack that contained the extinguisher has been decomissioned (a less tear-promoting term for dismantled), although the APW unit is still in my posession. A separate indicator would be useful, or since I doubt the thing actually works I could strip it for parts and use the detectors independently.

Leave a Reply

Your email address will not be published. Required fields are marked *