Re: Ion vs Photo smoke detectors

["FIRETEK" <firetech(change-the-ch-to-k)@telus.net>]

"Nomen Nescio" <nobody@xxxxxxxxx> wrote in message
news:83402837e45834b3ebfbb70be02106fe@xxxxxxxxxxxx
> 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.

In Canada, all fire alarm systems are engineered.  That means an engineer
signs off on the design and type of detectors he specifies.  In some
municipalities (such as Vancouver), an additional "test" is required be be
met and that is called the Vancouver Building Bylaw.  It's essentially based
on the BCBC (British Columbia Building Code), but it expands (details) some
additional requirements.

To give you some idea of what I mentioned earlier (and hopefully clarify
what I said), I'll detail some sections in CAN/ULC-S524-01 (Installation
Standard for Fire Alarm Systems).  This is a CANADIAN standard to which all
the Provincial Building Codes refer.  Keep in mind that, while this standard
is meant to be the definitive installation rule, it may still be subject to
interpretation by the local AHJ or even be modified by Building Code or
Bylaw.  In all the examples I'm going to cite, I won't be providing the
"local modifiers" (at least for the time being):

"5.6.2.5 Fire detectors in areas of high humidty, condensation, steam or
corrosion, shall be of a type compatible for such applications."

This rules out ion detectors in areas immediately adjacent to where they
could be subjected to steam or high moisture content (pools, spas, showers)
however the Appendix to S524 also has this to say:

"A1 General A1.1  Requirements of fire detectors can cover general
application rules only, and special circumstances not covered by this
Standard may arise.  Such circumstances require careful study of the
manufacturer's design guidelines, in accordance with good engineering
practices and shall meet the requirement of operating the device as
intended."

"A3.3  The application of smoke detectors canot be regulated by an
installaltion standard for the various types, environmental infuences, such
as thermal barriers, air movements and velocity variations, temperature,
atmostpheric pressure, relative humity, etc."

While this appears to let the people that write the standard "off the hook",
it places the correct use of the type of detector squarely back onto the
shoulders of the designer when it also states:

"A3.4 Manufacturer's recommendations should be carefully reviewed and used
in conjunction with these requirements.

A.3.5 In order for a smoke detector to respond, the smoke must travel from
the point of origin to the smoke detector.

A3.6  In evaluating any particular building or location, likely fire
locations should first be determined."

This section determines what kind of detector should be used as well as
where they should be located.  You are quite correct when you stated that an
"installer" (in this case a qualifed electrician) can not determine the best
detector for use in a given situation.  The Engineer/Designer will provide
that guidance based on his experience and knowledge of the code.  The AHJ
will also review this and the Verification Agency employed by the contractor
should be making the appropriate recommendation based on all of the above
referenced standards.  We have many "checks and balances" in effect here,
but not everything is "rosy".  For instance, a lot of "Verifying Agencies"
are "trained" employees of the manufacturers (or their designated reps) and
their "training" leaves a lot to be desired (as I've already noted in this
thread).


>
> 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.

Most installers don't.  That's the realm of the engineer and the individual
performing the verification.


>
> 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.

All of which are excellent points.  The "ideal" (perfect world scenario)
would remove the "interpretation" aspect from the codes and standards.  This
would ensure the kinds of things I've seen happen, don't.  Unfortunately
neither of us lives in "a perfect world" and we're forced to make the best
of it (hopefully with the help of a sympathic AHJ).