The Right Smoke Detector Saves Lives
By Mike Ward
While I was driving my son to school, I heard a news piece on the radio. The Bridgeport Firefighter’s Union was teaming up with Domino’s Pizza to check existing smoke detectors and install new ones at customer homes on Friday’s. While this is admirable, my fear is that they will use inferior smoke detectors.
There are two different technologies used in smoke/fire detection. The first and most commonly purchased or given out is the Ionization technology. The second and newer technology is the Photo-electric principle. When I was a Supervising Fire Inspector with the New York City Fire Department, I studied the use and effects of both types. Let’s look at each individually:
Ionization smoke detectors use an ionization chamber and a source of ionizing radiation (Americium 241) to detect smoke. This type of smoke detector is more common because it is inexpensive and better at detecting the smaller amounts of smoke produced by flaming fires. Smoke entering the ionization chamber disrupts the electrical current causing it to go into alarm. It can be identified by the nuclear hazard trefoil icon on the backside of the device.
Photo-electric smoke detectors uses a beam of light and a sensor set at 90 degrees from one another in its smoke chamber. Smoke particles cause the light to scatter and reflect the light onto the sensor causing an alarm.
There are 4 stages to a fire:
- Incipient stage – No visible smoke, no flame and very little heat. A significant amount of invisible (but sometimes smell-able) combustion particles may be created. This stage usually develops slowly.
- Smoldering stage – Smoke, but no flame and little heat.
- Flame Stage – Visible flame, more heat, often less or no smoke, particularly with flammable liquids and gas fires.
- Large amounts of heat, flame, smoke and toxic gases are produced. The transition from the previous stage can be very fast. This is also where Flashover can occur.
The Ionization (or ion smoke detector for short) is designed to detect a rapidly moving Flame Stage fire while the Photo-electric detects slow Smoldering Stage fires.
Most home fire fatalities occur due to products of combustion (Smoke inhalation) and asphyxiation which occurs when the fire consumes all the oxygen in the room. The thermal burns are a secondary cause and are either due to incapacitation by products of combustion or by exposure to a flashover. According the U.S. Centers for Disease Control and Prevention study of fires in 2008 on average, 1 fatality occurred every 151 minutes and injury occurred every 31 minutes. 4 out of 5 of these fatalities occurred in the home.
What this means is that by the time the Ion detector activated, the room was already filled with toxic gases and smoke, the oxygen levels have been depleted and the victim is showing signs of hypoxia (lack of oxygen), carbon monoxide poisoning or both and is incapable of rational though process.
Most stores carry the Ion detector for homeowner installation. They are widely available at any hardware store or home center and are relatively inexpensive. The problem with Ion detectors is they only detect burnt toast and generate what is called nuisance alarms. After the second or third one, most people disconnect them. Underwriters Laboratories actually lowered the sensitivity standard to prevent these false alarms.
By writing this I am not saying that the Ion detector is bad, they do have a purpose. I do not believe though, that it is the right detector for residential use. Any edge you can get to wake you and your family up earlier is worth the money spent.
Professional security contractors such as ADT, Slomin’s, Brinks Home Security etc. use and install the photo-electric detector into integrated home security systems. They are also available from home centers as a “single station detector” but you have to look for them or special order them. The other downside is they are a little more expensive.
A third choice is a combination detector. It employs either Ion/ Photo, Ion/ Carbon Monoxide, or Photo-electric/ Carbon Monoxide detectors.
In Connecticut, smoke detectors are required in all bedrooms with 1 additional detector being installed on each level of a home. Carbon Monoxide detectors are also required on each level of new construction homes and outside each bedroom area. Detectors should Never be installed in or within 3’ of a kitchen or bathroom containing a shower. Always follow the manufacturer’s instructions to the letter. If you have questions, contact the manufacturer, your fire department’s bureau of fire prevention or a licensed security professional.
Maintenance should not be forgotten either. According to manufacturer’s instructions, detectors of either technology should be tested monthly. Canned “smoke” can be purchases from hardware stores or home centers to test the device. Follow the detector instructions and the instructions on the can. This can be done in conjunction with a monthly home fire drill. Detectors should also be replaced after 10 years. You don’t keep your TV that long and it won’t save your life. A final word on testing: If you have an integrated home security system, call your monitoring center prior to testing the detectors so that they don’t dispatch the fire department on you.
Full scale smoke detector reaction time test of the differences between Ion and Photo-electric was conducted by the Barre City VT Fire Department. This video can be seen at either www.barrecityfire.org or www.smokealarminfo.com