optical smoke alarms

[Steve]

Can't think of anywhere else to put this. Can optical alarms be affected by sudden change of temperature? Twice now the alarm has activated shortly after the heating has come on. The alarm is a fire angel which I don't rate. I had a standard one which started with false alarms too.

 

[ericmark]

I had problems working at hight in the building. We knew where the beams went and we thought we could avoid them but it would seem we disturbed dust which set off the alarm.

I would expect something similar and the heating is causing either dust or an optical variation in the air like with a mirage so the beam is missing the receiver.

 

[sparkymarka]

Are you sure it's not a combination smoke detector ? Optical/ heat what model number is the unit ? These are becoming more common replacing the ionisation units.

 

[JohnW2]

Are you sure it's not a combination smoke detector ? Optical/ heat what model number is the unit ? These are becoming more common replacing the ionisation units.

Even if it were, one would not expect it to be activated by the room heating coming on.

Kind Regards, John

 

[ericmark]

I realise most smoke alarms do have some optical feature inside but I had assumed the poster was talking about the type which sends a beam through the roof space of a building with a sender and receiver.

Be it just hot tarmac or the sands of the dessert we see the effects of heat on light if the beam is central than normally there is not enough of an effect, but if slightly out heating could tip the balance.

 

[sparkymarka]

All guess work without the model number

 

[JohnW2]

I realise most smoke alarms do have some optical feature inside ...

'Optical' ones obviously do, but ionisation ones equally obviously do not.

... but I had assumed the poster was talking about the type which sends a beam through the roof space of a building with a sender and receiver.

I wouldn't have thought so - I was assuming we were talking about one in which the light beam was travelling between transmitter and receiver within the sensing chamber of the alarm, not 'through the roof space'. Indeed, I don't think we have any reason to believe that we are talking about within a roof.

sparkymarka seemed to be implying that if it were a combined smoke/heat detector, it could be the latter that was being activated by the heating system - but, as I said, one wouldn't really expect that - heat alarms generally require a very high temp to activated them, otherwise they would be producing false alarms all the time. However, as he also says, we really need to know exactly what alarm the OP has.

Kind Regards, John

 

[sparkymarka]

Rate-of-Rise (ROR) heat detectors operate on a rapid rise in element temperature of 12° to 15°F (6.7° to 8.3°C) increase per minute, irrespective of the starting temperature. This type of heat detector can operate at a lower temperature fire condition than would be possible if the threshold were fixed.

 

[JohnW2]

Rate-of-Rise (ROR) heat detectors operate on a rapid rise in element temperature of 12° to 15°F (6.7° to 8.3°C) increase per minute, irrespective of the starting temperature. This type of heat detector can operate at a lower temperature fire condition than would be possible if the threshold were fixed.

I didn't know the actual figures, but that makes sense. I presume that such a rate of rise is well beyond that normally to be expected when room heating comes on, otherwise such detectors would be a serious nuisance! I'm not sure that my CH could necessarily produce those sort of temperature rises in an hour, let alone a minute

Kind Regards, John