Best Fire Alarm Sensor Type, Optical or Ionization

Thread Starter

MrAl

Joined Jun 17, 2014
11,566
Hi,

I've been looking up fire alarms for sale because we have to replace some of the fire alarms in the house. These are the regular single type that work independently from the others.

Typical price runs from about $8 USD and up. The Optical with Ionization all-in-one types seem to be more expensive so I might not be able to get those kinds. So it's probably going to be one or the other type.

The two types are photoelectric and ionization.
I've been reading that photoelectric is better because it detects a smoldering fire faster than the ionization type.

What do you think, which one?
 

MisterBill2

Joined Jan 23, 2018
18,986
Battery powered alarms do have the inconvenience of yearly battery replacement, BUT they continue functioning when there is no mains power. And so if a mains issue starts a fire, that will probably matter. So there is something to think about, the choice has arguments on both sides.
 

nsaspook

Joined Aug 27, 2009
13,426
Don't go cheap with something as important as a fire/smoke detection. I've had a house fire before, they can save lives.
Wind blown embers burned the roof.
1709664661241.png
1709665325504.png
Forest fire embers all over the car. Bone dry conditions.

The only cloud networked system in the house are the Nest Protect wifi detectors. The Pathlight and other features are brilliant and are totally reliable (10 year battery life with notification and auto daily sensor checking) even with the wireless disconnected.
1709663693745.png
https://www.nytimes.com/wirecutter/reviews/best-smart-smoke-alarm/
 
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ronsimpson

Joined Oct 7, 2019
3,144
I agree, install different types.
I like the Carbon Monoxide type. Most house fires start out small and without enough Oxygen. This causes CO.
A kitchen fire starts out big. The CO type does not do as well.
I am going to install an attic alarm and a crawl space alarm. I have seen attic fires that never set off an alarm.
In my garage is the hot water heater, furnace, and cars, all of which can cause fire. I have an alarm there because, in my case, the garage is the most likely case.

Any alarm is better than no alarm and the right alarm is better yet.
 

Dodgydave

Joined Jun 22, 2012
11,318
Hi,

I've been looking up fire alarms for sale because we have to replace some of the fire alarms in the house. These are the regular single type that work independently from the others.
Typical price runs from about $8 USD and up. The Optical with Ionization all-in-one types seem to be more expensive so I might not be able to get those kinds. So it's probably going to be one or the other type.

The two types are photoelectric and ionization.
I've been reading that photoelectric is better because it detects a smoldering fire faster than the ionization type.

What do you think, which one?
I used to be a fire alarm service engineer and asked this question many times by the customer, fit both types.

Optical detectors work on smouldering fires like furniture they are less likely to false alarms, they work by bouncing infrared light off the particles of smoke and the receiver picks up the light reflecting and triggers an alarm.

Ionisation are faster but prone to false alarms, and use a bit of radioactive material in a small metallic chamber and produces a change in current when the air gets contaminated with smoke particles , these are good for flaming fires with little smoke, but they are gradually being phased out.
 
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Thread Starter

MrAl

Joined Jun 17, 2014
11,566
Hello again,

A very nice person I know went out and bought new smoke detectors for here. They are both photoelectric and chemical (for carbon monoxide detection). They have been installed this afternoon sometime after I started this thread.
However, that doesn't mean that I will not get the other type too.
BTW they were $50 each and they have a 10 year non-accessible battery, which means someone cannot take the battery out to make it stop working when they cook stuff. However, they have a 'pause' button that will stop them from sounding for 10 minutes if it is pushed in.
 

Thread Starter

MrAl

Joined Jun 17, 2014
11,566
I used to be a fire alarm service engineer and asked this question many times by the customer, fit both types.

Optical detectors work on smouldering fires like furniture they are less likely to false alarms, they work by bouncing infrared light off the particles of smoke and the receiver picks up the light reflecting and triggers an alarm.

Ionisation are faster but prone to false alarms, and use a bit of radioactive material in a small metallic chamber and produces a change in current when the air gets contaminated with smoke particles , these are good for flaming fires with little smoke, but they are gradually being phased out.
I was originally asking for arguments for and against each type because I only intended to install one or the other, as I said in my first post. However, things have changed now that a neighbor bought them and we have them installed now too. They are photoelectric and chemical for CO2 detection.
I may get the other type now too since I didn't have to pay for the photoelectric/CO2 ones, and most of the suggestions here have said to get both.
 

nsaspook

Joined Aug 27, 2009
13,426
Ionization alarms are not allowed in my state.
You mean in homes, not totally.

There are classes of fires not easily detect by photoelectric, like methanol fires that don't produce much soot so the obscuration is low.
 
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BobTPH

Joined Jun 5, 2013
9,149
You mean in homes, not totally.

There are classes of fires not easily detect by photoelectric, like methanol fires that don't produce much soot so the obscuration is low.
Yes, in homes. Unfortunately, steam triggers photoelectric alarms.
 

nsaspook

Joined Aug 27, 2009
13,426
Yes, in homes. Unfortunately, steam triggers photoelectric alarms.
Why was it banned in homes there? A quick search says only three states have restrictions.

https://www.cityofboston.gov/fire/pdfs/smokealarmlaws_jan2010.pdf
Consequences of Different Alarm Technologies The difference in operational technology between the two alarms is the reason for the ionization alarms higher sensitivity to fast-flaming fires, which produce small particle smoke. It is this same technological difference that causes ionization alarms to be most sensitive to "invisible smoke,” i.e. nuisance alarms," while at the same time photoelectric alarms are virtually insensitive to invisible smoke. The operational differences also explain why the photoelectric alarm is far more sensitive to smoldering smoke, which generally contain larger and fewer particles than smoke from flaming fires.
You can still use dual sensor Fire Alarms, right?
 
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camerart

Joined Feb 25, 2013
3,731
Hi Mr A,
I'm not sure what type they are but there are kitchen alarms, that sense heat not smoke, so don't go off if the toast is burnt.
C
 

Ya’akov

Joined Jan 27, 2019
9,236
Just for posterity, should this thread end up in someone’s web research:

First Alert sells “wireless interconnected” detectors that will all sound if one is triggered. This can be very important if your house is large or some rooms are isolated from others sufficiently to make the detector’s sounder hard or impossible to hear.

This model includes a voice announcement to indicate which detector is in alarm so it is possible to know how to evacuate safely.

They also sell Z-Wave equipped sensors which can connect to a number of home automation systems so lights, sirens, phone alerts, &c. can be activated by a detection.
 

Dodgydave

Joined Jun 22, 2012
11,318
Hi Mr A,
I'm not sure what type they are but there are kitchen alarms, that sense heat not smoke, so don't go off if the toast is burnt.
C

They use a thermistor for heat sensing, some are rate of rise others use fixed temperature, they won't detect smoke that's why these are in kitchens..
 
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