Ionisation or Optical/Photoelectric smoke alarm?

[CAWORK]

HI Everyone

In my parents home I installed two smoke alarms three weeks back, an ionosation at the top of the stairs with an escape light and an optical in the living room near the meter and consumer unit area.

I done the latter thinking an electrical fault around here would smoulder first and an optical alarm would be most suitable.

Could anyone enlighten me on this please?

Am I right in what I have done?

 

[breezer]

iddealy you should have both

but your thinking is not wrong.

 

[^woody^]

I wonder what the actual delay time will be between the two types?

Probably milliseconds

 

[breezer]

woody, it depends on the type of fire as to the answer to that question.

Optical smoke detectors work by seeing almost any size of smoke particle

ionisation smoke detectors are looking for "smouldering material" not smoke.

it has been known for some ionisation detecotrs to be in a room full of smoke and not activate because they cant sense it

Ionisation are good for detecting pre smoke*, optical are good at detecting smoke

*but it depends on what is causing the fire as to if it will work or not

 

[mattylad]

Breezer, (not wanting to argue but) where so you get that information from?

Speaking as someone who has just been discussing this with the designer who designs all types of professional smoke detectors, your statements have been said to be mixed up. Its the other way around.

Optical detectors are better at detecting smouldering fires.

Ionisation detectors need a much larger particle size

So

Ionisation are good for detecting pre smoke*, optical are good at detecting smoke

should actually be:

"Optical are good for detecting pre smoke*, Ionisation are good at detecting smoke"

ionisation smoke detectors are looking for "smouldering material" not smoke.

Does not appear to be correct either.

AFAIK In household situations, optical detectors are best as they will detect the smouldering fires quicker yet are less likely to go off when your burning the toast.

 

[breezer]

we will have to not agree

are you saying that an ionisation detector will detect tiny particles of smoke?

since you said

should actually be:

"Optical are good for detecting pre smoke*, Ionisation are good at detecting smoke"

 

[mattylad]

I have had another chat with the guy wot knows & I get a lot of "ifs" of him.
If this, if that etc.
It seems to boil down to:

Ionisations are good at detecting small particles from a freely burning fire where there are a lot of particles.

Opticals are good at detecting the larger particles where there are a lot less I.E. from a smouldering fire.

Hence where the room full of ionisation detectors takes longer to detect a fire than optical ones.

Opticals appear to come out the best in household situations & where a smouldering fire needs detecting.

An aspirating system would be better though (detecting a fire down at the very smallest particle size) so we all need an IFD type system installing - lol (Hey, what do you expect when your talking to a manager, they are dizzy at the best of times).