Re: Ion vs Photo smoke detectors

[Nomen Nescio <nobody@xxxxxxxxx>]

FIRETEK said:

>When you read through
>the standards we use (CAN/ULC-S524 for instance), the requirement for using
>the correct detector is clear.  How this passes the Verification is
>sometimes beyond me.

I am curious as to what requirements are in your Canadian standard for the
use of ionization vs. photoelectric detectors.  US standards really do not
address this issue, probably for fear of pissing off one detector
manufacturer or another.  In my opinion, it is beyond the skill level of
the average fire alarm system designer to determine which type of smoke
detector will provide the optimal response to a fire in a particular
building, with its specific contents.  A fire protection engineer might be
able to hazard an opinion on that, but the average fire alarm designer has
neither the training nor the expertise to make those calls.

Everyone knows the conventional wisdom is that ionization detectors detect
flaming fires faster and photoelectrics detect smoldering fires faster.  My
point is that I don't really know what kind of fire is likely to occur in a
particular building.  I don't have that kind of training.

For me, it's a much simpler analysis.  Ionization detectors cause lots more
false alarms than photoelectrics.  If prompt detection of a flaming fire is
a design spec, put in some rate of rise detectors.  They do a great job of
detecting flaming fires, since they produce lots of heat.  They also cover
a larger area than ionization smokes, and their false alarm rate is nearly
zero.

Ionization smokes weren't invented because they were better.  They were the
original smoke detectors, and we've been stuck with them ever since.
Especially since the smoke alarm manufacturers discovered they could make
them cheaper than photoelectrics.

- badenov