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Fire Alarm -- Testing

Often when testing smoke detectors canned smoke is used.
Smoke detectors have to detect a wide range of smoke. People often wonder if canned smoke mimics real smoke or is there something better to use for testing.
Douglas Krantz -- Fire Alarm Engineering Technician, Electronic Designer, Electronic Technician, Writer






Should Canned Smoke be Used to Test Smoke Detectors?

By Douglas Krantz

There have been many discussions about the best way to test smoke detectors --- canned smoke or real smoke. The problem is finding something to test with that mimics fire without burning down the building.

Smoke Detectors Don't Detect Fire

Most fire detection devices don't detect fire; most fire detection devices detect "products of fire".

Heat detectors only sense that the temperature is above a certain level, or that the temperature is rising. They can't tell if a fire caused the temperature to rise, or that the boiler room is just a little hotter than normal.

Waterflow switches only sense that water is flowing in a pipe, or that the pressure in the pipe is above a certain level. They can't tell if a fire was causing the water to flow, or if a ladder broke a sprinkler head causing the water to flow, or if the pipes froze and broke causing the water to flow.

Smoke detectors only sense that there are particles in the air. They can't tell if the particles are smoke caused by a fire, or the particles are smoke caused by overheated bacon, or if the particles are spray paint.

Smoke Detector False Alarms

Smoke detectors, though, are more susceptible to false alarms because what they see as smoke can be so many other things.

Smoke Isn't Fire

First off, smoke is a byproduct of fire. Most of the time, not being fire, smoke is actually unburnt fire fuel. It comes in a huge variety of particle sizes and colors, and some of the particles are solid while some of the particles are liquid.

Just from a single fire, there are lots of variations in the particles --- and the mixture changes as the fire progresses. To make smoke particles more difficult to catalog, each fire produces different smoke variations from any other fire.

Smoke Detector Chemical Analyzing

The problem is that smoke detectors can't perform a full chemical analysis; they can't determine the chemical makeup of smoke.

In a kitchen, for instance, smoke detectors have a difficult time detecting the difference between a grease fire and Cajun cooking. The percentages of the particulates may be slightly different, but the detectors just aren't able to tell the difference.
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Different Kinds of Smoke Detectors

Just to make smoke detection more interesting, smoke detectors themselves come in a number of varieties. Some are more sensitive to large particles and some are more sensitive to small particles; some are more sensitive to light colored particles and some are more sensitive to darker colored particles.

Testing Smoke Detectors

When testing, it would be easier to say what is better, canned smoke or real smoke --- except there is no canned smoke or even real smoke that mimics all the different varieties of fire caused smoke.

Using the Manufacturer's Testing Method

With all these variations --- smoke variations and detector variations --- it would probably be best to test smoke detectors using the manufacturer's recommended method.






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Douglas Krantz

Describing How It Works
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Electrical Flow


On this website, most references to electrical flow are to the movement of electrons.

Here, electron movement is generally used because it is the electrons that are actually moving. To explain the effects of magnetic forces, the movement of electrons is best.

Conventional current flow, positive charges that appear to be moving in the circuit, will be specified when it is used. The positive electrical forces are not actually moving -- as the electrons are coming and going on an atom, the electrical forces are just loosing or gaining strength. The forces appear to be moving from one atom to the next, but the percieved movement is actually just a result of electron movement. This perceived movement is traveling at a consistent speed, usually around two-thirds the speed of light. To explain the effects of electrostatic forces, the movement of positive charges (conventional current) is best.

See the explanation on which way electricity flows at www.douglaskrantz.com/
ElecElectricalFlow.html
.