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Time to change clocks and check smoke alarms

Standard time officially returns Sunday at 2 a.m.
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Sunday’s time change - when clocks are turned back one hour for Standard Time - serves as a good reminder to test your smoke alarms and change the batteries. “Working smoke alarms save lives, reduce injuries and damage. Have you tested yours?” is a message from the crew at Kootenay Boundary Regional Fire Rescue, including Captain Jason Milne (left) and firefighter David Como.

Information from Kootenay Boundary Regional Fire Rescue about the importance of installing and checking smoke alarms:

Smoke Kills People

It’s a fact! Smoke causes the majority of fire-related deaths. Hot flames are low on the list of killers during a fire. Smoke contains deadly killer gases such as carbon monoxide and, when smoke is produced, life-sustaining oxygen is consumed. Most fire victims die from these factors, frequently before they awaken. In many fires, extinguished in early stages, people have been found dead of smoke inhalation without having suffered any skin burns.

A smouldering fire may go undetected for hours, especially when people are asleep. Such a fire will continue developing, giving off smoke and gases which may not be visible but which consume oxygen and replace it with toxic gases.

In addition to the deadly killer carbon monoxide, smoke carries poisons such as hydrogen cyanide plus irritants such as formaldehyde and acetic acid. Added to this deadly environment are the toxic substances that come from burning synthetic materials commonly found in the home, especially plastics. Oxides of nitrogen, sulphur dioxide, and ammonia are just a few examples. These killer agents can take effect before a sleeper is disturbed. An early warning system - a smoke alarm - is considered one of the most effective defences against this situation.

Stages of Fire

Understanding the sequence of events in a residential fire makes it easier to appreciate how smoke alarms can provide a time margin that can save your life. Most fires progress through four distinct stages - first the incipient stage, next the smoke stage, next the flame stage, and finally the high-heat stage. Smoke alarms can alert the occupants in these early stages of a fire while conditions are such that a safe evacuation is still possible.

What Are They and How Do They Work?

A smoke detector is, essentially, an assembly of electrical components arranged to detect one or more products of combustion. The products of combustion may consist of gases, water vapour, and visible as well as invisible smoke particles. Smoke detectors work by sensing these products of combustion and sounding an alarm. They can detect smoke far from the origin of the fire. Basically there are two types of smoke detectors, ionization detectors, which respond to visible and invisible smoke particles or aerosols, and photoelectric detectors, which respond to visible smoke.

Smoke Alarms are now being marketed that provide dual detection. These units contain both an ionization detection chamber and a photoelectric detection chamber and operate on the same principle as either a single photoelectric or a single ionization alarm. Dual detection smoke alarms offer the advantages of both types in a single unit.

Which Detector is Better

Both ionization and photoelectric detectors, if properly installed and maintained, are effective. Since photoelectric detectors react more quickly to smouldering fires and ionization units will respond faster to flaming fires, you may wish to buy one of each, or a combination detector. However, because most home fires produce a mixture of smoke types with detectable amounts of large particle and small particle smoke early in the fire growth, either a photoelectric or an ionization detector will meet most needs.

Several new features are available in smoke detectors today. These include detectors that have an escape light, are portable, or transmit their alarm to a central console by radio signal as part of a unified emergency alert system. Electric current detectors with a rechargeable battery for power outages are also available.

Ionization Detectors

Ionization detectors respond to both invisible and visible products of combustion. The particle size that the ionization type of detector best responds to are particles in the .01 to 1.0 micrometer range. Particles smaller than approximately 10 micrometers are invisible to the human eye.

The detector relies on an ionization chamber for the detection of the aerosol fire signature. The ionization chamber consists of two metal plates separated by an air gap, which is open to the atmosphere. Between the two metal plates, which are referred to as the anode and the cathode, is a minute quantity of radioactive material, usually Americium 241. The quantity of radioactive material used is approximately 5 micro curries. The purpose of the radioactive material is to ionize the air between the two plates resulting in a weak flow of electric current. When particles such as those produced by a fire enter the smoke chamber, they reduce the current and trigger the alarm.

Photo-Electric Smoke Detectors

This type of detector contains a chamber with either overlapping or porous covers which prevent the entrance of outside sources of light but which allow the entry of smoke. The unit contains a light source and a special photosensitive cell in the darkened chamber. The cell and light are positioned within the alarm in one of the two manners: either the light beam is interrupted by the smoke as in the obscuration type or, the beam is deflected into the cell as in the light scattering type.

How Many Detectors Should (Must) I Have?

Most municipalities have bylaws requiring a smoke detector outside (or in the common hallway of) each sleeping area in a residential home. It is best to check with your local Fire Department to find out what is required in your municipality. They can also offer advice on detector placement, testing and, maintenance.

The location of the basic smoke alarm in the vicinity of sleeping areas does not provide sufficient protection for the occupants from a fire starting in their bedroom with the door closed. It may be desirable, therefore, particularly if you smoke, to have additional alarms within each bedroom itself, and in other areas such as basements, family rooms, etc.

Research indicates that substantial increases in warning time can be obtained with each, properly installed, additional alarm.

A closed door can delay the movement of smoke, preventing it from reaching a smoke alarm, and fire confined in a large room often develops great intensity before it breaks out of the room. The basement is one area that can be large, remote from the alarm, and isolated by some type of closure at the top of the stairs such as a door. Basements also account for a significant number of fires. For these reasons, it is recommended that the smoke alarm be placed at the head of the stairs from the basement.

A smoke alarm is also recommended at the head of each stairway leading to an occupied area. This location may also serve the purpose of protecting a sleeping area in a two-storey house if the room layout is suitable. Whether or not you choose to add the additional units, at least install one basic smoke alarm.



Sheri Regnier

About the Author: Sheri Regnier

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