Smoke detectors

I am installing a burglar alarm in my workshop, it has the option to add smoke detectors. Simple to do, but what type is best to use.

I probably wont use suds and use neat oil instead, so there will be some smoke. Plus stick/mig welding and blowlamps.

I have a choice of;

• Optical smoke detector
• Combined Optical smoke and fixed heat detector
• Fixed heat detector
• Rate of temperature rise detector.

Any one got any thoughts or had experience of detectors?

My only experience is that I can't cook steak in my kitchen without the smoke alarm in the hall going off.

My thoughts - a smoke alarm connected to an alarm is probably only active when the alarm is set, so there should be no new smoke or temp rise when in use so the cutting oil or brazing ought not be an issue.

Edited By Nick Clarke 3 on 24/03/2019 09:38:24

After a shed fire a few years ago, I have two smoke alarms.

Not sure what type they are, but they will go off if have carried away with cutting oil! I take that as the reminder to switch on the extractor!

Jim

In a former life, I used to service the Fire and Gas installation where I worked...

So to answer your questions...I offer the following:

Rate-of-Rise (ROR) heat detectors operate on a rapid rise in element temperature, irrespective of the starting temperature and can operate at a lower temperature fire condition than would be possible if the threshold detection point was fixed.
A fixed temperature detector operates when the heat sensitive element reaches the point of changing state from a solid to a liquid. there is a delay due to thermal lag in the accumulation of heat at the sensing element so that a fixed-temperature device will reach its operating temperature sometime after the surrounding air temperature is a lot higher. Potentially there may already be a fire!
Smoke detectors come in three flavours...optical, ionization and a combination of both.
Most installations for domestic use, use the optical detector, in industrial applications the ionization type requires a licence because of the radioactive element contained within.

If you do go for smoke and heat, dont forget to have a testing regime in place.....We tested our systems every three months...

I've arranged the smoke alarm in my workshop with a normally closed relay between the battery and the circuit so you can press a button to disable it. The relay is fed off the lights, so when you turn the lights off the relay de-energises and the alarm is connected up again. You have to remember to press the button before starting any silver soldering jobs, but smoke from cutting oil doesn't seem to affect it. There again, I'm a bit pussyfooting when machining, cutters cost too much to be aggressive

'In a former life' likely means out of date?

Both my domestic smoke detectors are old tech and have Americium-241 sources. Go figure.

Resistance wires and other technology, these days, likely reduce the time lag for temperature change to a minimum.

Take advice from a respected installer is my advice. I am lucky in that a good friend of mine still runs a security business.

Hi

The domestic smoke detectors I have running and those which have been replaced are/were all 'ionization' devices. The one near the kitchen had an override as it will activate from fumes from the cooker grill/oven when there is no smoke in the air. That said I haven't checked on the latest domestic alarms to see if they have changed the type of sensor used.

MartinW

PS

Just checked the Screwfix site and they are now offering a full range of detectors including heat and smoke combined. Tomorrow I will purchase a couple, offered in pairs, to fit near the kitchen or even have one in the kitchen. Thanks for the heads up.

Edited By Martin W on 24/03/2019 11:32:18

Surely the biggest problem with workshop smoke alarms is this; most workshops are probably in an outside shed with nobody there when the alarm goes off. I suppose some form of remote sensing could be used so that an alarm went off inside the house in the event of a workshop fire.

Doug

Edited By John Rudd on 24/03/2019 13:36:48

OOH! I like that!!

ROR would be best for a workshop, I assume that if you are in there, you will be aware it is on fire (ie, its not that large and only has one level), and will take appropriate action. Smoke detectors will be a nuisance, and are affected by all sorts of vapours, and also we have lots of problems with tiny insects mistriggering them. Fire extinguishers! I keep two CO2 a foam and a Water around the shop , best have a couple available outside the workshop to fight your way in! I had one serious workshop fire many years ago, when some hot metal from welding a sill (had the car on a roller) went straight through a plastic fuel pipe (I had checked at another point, where is was metal!) Whenever I start welding, I get an extinguisher, pull out the pin, and put it next to where I am working. Picked it up and put the fire out in seconds! My mate was half way to the next county! Not saying there is not a time when you should leave it to burn, just that if you are prepared for a fire, you can usually avoid that ever happening.

The detector will be hooked into one of the zones on the alarm panel so when you disarm the alarm the smoke detector will not work you won’t need relays or switches just buy the detector that is made to hook into your panel from the same place you bought it , i would probably use the smoke type detector as it will pick up something that is starting to burn before flames set in but if you can get one that does smoke and flame all in one unit that would be even better. Some alarms have the capability to call a phone to alert you but they cost more . I used to have an alarm in my old workshop that used pir sensor and i eventually got sick of climbing out of bed in the middle of the night to reset the alarm because of false alarms (never did find out what was triggering it )i now use reed switches on the doors and windows instead .

I added fire detectors in my workshop...too much smoke!

we recently had the chimney sweep round and he is a fireman in his proper job, he, no the fire brigade recommends smoke angel alarms sited in the escape route

Thanks for the advise, I think I will go with a ROR in the workshop, then put a combined unit in the attached store room.

BTW as far as I can understand the instructions, these types of detector are latching. Once triggered they stay activated till they are reset (remove from socket). So if the alarm was configured to see them as entry detectors you would not be able to set the alarm till you reset them.