The Ultimate Smoke Detectors Quiz

Some 400,000 residential fires occur in the U.S. each year. Many of these could have been prevented.

Washers and dryers that were not cleaned properly were responsible for some 60,000 fires in the U.S. between 1999 and 2002.

Despite what many people may think, chimneys cause more fires than space heaters. In addition, although many people believe that fires are started when a candle is knocked over, about half of fires caused by candles start because of combustible material placed too close to the candles.

Loose clothing and clothing with strings or parts hanging off of them are more likely to end up in a hot pot or in a flame and cause burns. Wearing tight or fitted clothing when cooking may prevent this.

You can buy smoke detectors for as little as $7. Given the thousands of lives they save each year, they are definitely a worthwhile investment!

Smoke detectors generally run off a 9-volt battery. They may also run on 120-volt house current. Smoke detectors are made of two parts: one part senses smoke and the other part makes a loud noise to alert people to the smoke.

Usually photoelectric detectors, such as those used on a shop door, are made from a light shining onto a detector. If the signal is blocked, for example if someone walks through it, then a bell is triggered. In smoke detectors, the light sensor is placed at a 90 degree angle to the light beams. Smoke particles that enter the smoke detector cause the light to scatter, bending some of the light rays onto the light sensor and triggering an alarm.

Using a normal photoelectric detector would require a lot of thick smoke to completely block out the light and set off the alarm. The light sensor in a smoke detector is set up so that, even if just a few of the light beams are scattered onto the sensor, the alarm will sound. Photoelectric detectors are better for sensing smoky fires, like a smoldering mattress.

Americium-241 is the radioactive element used in an ionization smoke detector. Only 0.9 microcurie is used (or about 1/5000 of a gram).

Americium has a half life of 432 years, so you wont need to worry about it running out any time soon.

The curie, named after the scientist Marie Curie, is a unit of measure for nuclear material. It means that if you are holding a curie of something in your hand, it is undergoing 37 billion nuclear transformations per second.

Alpha particles are emitted by americium-241. Alpha particles cannot penetrate a sheet of paper or more than a few centimeters of air. This makes them quite safe to use in smoke detectors in terms of radioactivity. However, it is advisable not to poke, prod or disturb the americium in any way as this could cause alpha particles to become airborne and lead to inhalation of the particles, which can be dangerous.

Alpha particles ionize oxygen and nitrogen particles in the smoke detector chamber. This means that an electron is knocked off of the oxygen or nitrogen atoms, resulting in a free electron with a negative charge and an atom missing an electron which gives it a positive charge.

The positively charged atoms are attracted to the plate with the negative voltage and the negatively charged electrons are attracted to the plate with the positive voltage. The smoke detector is set up so that the electrical current produced by the charged particles moving towards the plates is sensed by the detector system.

Smoke particles attach to the ions in the chamber and neutralize them. This causes a drop in the current between the plates, which is sensed by the smoke detector and triggers an alarm.