What Are the Differences?
In order to illustrate this better, think of smoke in terms of water. Ask yourself this question - What is the difference between water from the tap and the steam coming out of your shower? The answer is temperature. It is still water, but because the water coming from your shower is hotter, it is in the form of steam. The particle sizes are smaller. Smoke acts the same way, the hotter the smoke, the smaller the particles. The colder the smoke, the larger the particles.
Taking this a step further, what happens to the steam as it travels away from the shower? It cools down. As it cools, the particles combine with other particles eventually creating water droplets that you can see on the walls and windows. Again, the same is true of smoke. As the smaller, hot particles travel away from the heat source, the individual particles cool and combine with other particles. This is a process called agglomeration. The cooler they get, the larger the particles become. If this hot smoke has to travel a distance to reach an ionization smoke alarm, it may have cooled sufficiently to essentially create cold smoke. This cold smoke with larger particle sizes may not activate the ionization alarm. However, regardless of the distance traveled, this same smoke will activate the photoelectric alarms simply because of how the alarms operate.
So what do we do now? Education and legislation - we need to make sure that the differences between these types of detectors are known by everyone. If the public really understood the differences and how unprotected they are without both types, most folks would take care of themselves. Additionally, we need to push law makers to force home builders and manufactures to include both technologies in the homes they build.
Here in Barre City, we are advocating duel sensor smoke alarms, those with both ionization and photoelectric sensors built in. There is no way to tell where a fire will start, or what type of fire you will have. A dual sensor smoke alarm will protect against both types. Existing homes can either replace the ionization alarms with dual sensor alarms, or supplement them with photoelectric alarms. In kitchens, where the ionization alarms are routinely activated by cooking which then causes the occupants to remove the batteries, we are advocating stand alone photoelectric alarms. This will cut down on these nuisance alarms and the likelihood that the batteries will be removed causing the alarm to be ineffective.
Carbon Monoxide vs. Smoke Alarms
When you add carbon monoxide (CO) alarms to the mix, you are now talking about three technologies. We are advocating a stand alone CO alarm. There are two reasons for this. First, CO alarms need to be replaced every five years where smoke alarms need to be replaced every 10 years. When you combine a CO and smoke sensor in one detector, that detector is only as good as its weakest link and in this case, the CO sensor, is just five years. The other reason is how CO travels in the spaces. Because it is essentially the same weight as air, CO travels with the normal air currents. We advocate placing CO alarms at the same level of the heads of the sleeping occupants on the floor they sleep on. If there is a second CO alarm, we advocate that one to be placed closer to the ceiling, again, on the floor they sleep on. It goes without saying, however, that each floor should be protected with alarms.
Cost is a huge factor for everyone. Dual sensor alarms cost more than a stand alone photoelectric or ionization alarm. The dual sensor alarms in my home cost about $23.00 each, where a stand alone photoelectric costs around $12.00. For folks that are not able to afford the dual sensor alarms, we tell them to use a stand alone photoelectric alarms. Even though it is slightly slower than the ionization alarm at detecting a flaming fire (30 seconds or less on the average), it is considerably faster at detecting a smoldering fire (30 - 40 minutes on the average). It is these smoldering fires at night that are the most deadly.
As a fire service, we tell people to protect themselves with smoke alarms. Although we have not been wrong, we have not been completely right either. We still have a huge problem in this country of homes without any smoke alarms, and any smoke alarm is better than no smoke alarm. But we need to tell the public to have both types of technology in their homes. It is their families at stake. It is your families at stake. The only hope we have to get out of a burning building at night is for our smoke alarms to sound early. If they don't, the occupants will die. We know. We saw it.