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If Your Cooking Skills Are Like Mine, Maybe You Should Know How a Smoke Alarm Works

November 18, 2013

Smoke alarmTwo nights ago I decided to make an amazing chicken dinner to surprise my boyfriend when he got off of work. I had marinated the chicken in the fridge all day, I had the vegetables all chopped up and ready for the salad…and I turned on the oven to begin its preheating. My boyfriend came in the door less than ten minutes later to a billowing black cloud of smoke, a screeching smoke alarm, and a frantic panicking me, shouting, “WHAT DID YOU DO?!?!” as I was shooing the dog out of the kitchen so I could get the oven turned off, fling open windows, and get the situation sorted out.

Thankfully no fire started—not so thankfully my boyfriend got a lecture about why not to leave empty pizza boxes in the oven (I’m still not sure where this idea of his came from). Long story short, the paper box had started smoking from the heat, filled up the house with smoke, and set off the smoke detector, leaving me in a panic.

If anyone reading this is an awesome chef like I am, they will probably be thinking one of two things: first, “Why didn’t you check to see that the oven was empty before turning it on?” or second, “I’ve made my smoke alarm go off a time or two while cooking.”

But what  got me thinking, other than making a mental note to be sure my condo insurance policy was paid up for the month, was how my smoke detector worked (because I really am that much of a nerd). How do they know when to alert us to a possible fire danger in our home?

What I learned is that there are two types of smoke alarms used in homes in the US: ionization detectors and photoelectric detectors… and those ionization detectors involve a lot of science.

Ionization detectors have an ionization chamber with two plates and a source of ionizing radiation and a battery sending voltage to the plates. Inside the detector is a small amount of americium-241. Americium generates alpha particles which ionize (knock an electron off of an atom), which results in a “free electron” or an electron with a negative charge, as well as an atom missing an electron (high school chemistry taught us that this means the atom has a positive charge….don’t worry, I didn’t do well in high school chemistry either). The negative electron will be attracted to the plate with a positive voltage (like in dating: opposites attract!) and vice versa for the positive atom and negative plate.

When smoke particles enter this ionization chamber, they disrupt this current and neutralize the ions, and the detector will sense a drop in the currents and set off an alarm. Nuclear radiation is alive and well in your homes, folks! No need to be alarmed, though; the amount of radiation used in this type of detector is extremely small and includes “alpha radiation,” which, according to my internet sources, cannot penetrate a sheet of paper. This type of smoke alarm is relatively inexpensive and one of the more common ones available. Ionization detectors are also prone to false alarms…. If any of you lived in a college dorm with an ultra-sensitive smoke detector (at 3 AM), it was probably because of one of these picking up steam, dust, or other vapors.

The photoelectric detectors are much simpler to understand. They include a T-shaped chamber and a light-emitting diode. The light is sent across the top of the T and at the base is a photocell that detects light. When smoke enters this type of alarm, the light is hit and gets scattered to the base of the alarm (where the photocell is) and sets off an electrical current which sounds the alarm. A photoelectric detector is not as sensitive as the ionization ones (you probably won’t set it off from too much steam in your pan on the stove) and tend to respond to smokier fires.

Whatever kind of smoke alarm you choose for your home, just remember that they don’t work if they’re still in the box (or if the batteries are dead!).  As thanks (or punishment?) for the chicken dinner incident, my boyfriend spent an hour in between Sunday football games on a ladder testing and replacing the batteries in all of our smoke alarms.

Article by: Kristen Skinner

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