Should radioactive smoke alarms be a compulsory purchase?

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Finn O Hurley

Should radioactive smoke alarms be made a compulsory purchase for all home owners in the UK?

I am going to discuss whether radioactive smoke alarms should be made a compulsory purchase for home owners in the UK.  I will describe how they work and their advantages and disadvantages.  I will also examine an alternative to radioactive smoke alarms and describe its advantages and disadvantages.  Using data from the fire and rescue service I shall identify trends and patterns I have found for fires that have occurred over the last few years, both with, and without smoke alarms.  Finally, based on my research I shall give my opinion on which smoke alarms are the best, whether more than one type of smoke alarm is desirable and whether the purchase of radioactive smoke alarms should be compulsory for home owners in the UK.

Diagram 1

A radioactive smoke alarm works in a similar way to the human nose in that it uses a kind of chemistry to spot unusual molecules (smoke) heading inward.   The alarm contains a radioactive form of a chemical element called Americium 241. The americium 241 is placed beside a small ionising chamber.  The chamber consists of two plates connected to a battery.  As I said, Americium 241 is radioactive which means it is unstable and is trying to stabilise itself by emitting alpha particles.  Alpha particles have a charge of +2, and are made of two protons and two neutrons. Because of their charge, they ionise (combine with other particles to produce positive or negatively charged particles) very quickly.  When the alpha particles enter the ionizing chamber they collide with the air particles it contains and ionize them.  This means that the atoms within the chamber lose one electron, leaving a positively charged atom. The electron and positive atom are ions. The negative ions (electrons) are drawn to the positively charged metal plate, and the positive ions (the positive atoms) to the negative plate. The small current generated by this flows between two electrodes.   As long as the current flows in this way the alarm does not go off.  But if a fire breaks out and smoke is present in the air, the smoke molecules attach themselves to the ions and neutralise the ions.  This shuts off the electric current.  The circuit in the detector spots that change straight away and sounds the alarm.

This type of smoke alarm has a number of advantages and disadvantages.  One advantage is that it is cheaper-this is an advantage because high cost might put people, especially less well off people, off buying an alarm which could ultimately cost lives.  Another advantage is that these alarms are quick to detect fast flaming fires (such as chip pan fires) with little visible smoke.  This is an advantage because it alerts the occupants of a house quickly and gives them a chance to get out before the fire spreads too far and the smoke becomes dangerously thick.  However, this type of alarm also has a number of disadvantages.  It is slow to respond to small smouldering fires.  This might mean such a fire might spread over a large area and then develop into a fast flaming fire before the family have a chance to be alerted and escape.  It is also more likely to go off due to food being burnt during cooking which might make the alarm a nuisance and lead to people deactivating it and forgetting to reactivate it later which could have fatal consequences.  Lastly, the fact that it contains radioactive material may put people off buying it as radioactivity is very harmful to human health (though the radiation dose from a household smoke alarm is less than background radiation).   

A different type of smoke alarm is an optical or photoelectric smoke alarm. This alarm is like an electronic eye, it works by “seeing” the visible smoke particles.  This kind of detector is screwed to the ceiling because smoke rises when something starts to burn as fire produces hot gases that are less dense than ordinary air and rise upward carrying smoke particles with them.  An opening in the bottom of the detector (1) leads to a chamber above. An infra red light shines across the chamber from a light-emitting diode or LED (2) to a photocell (3). The photocell is an electronic light detector that generates electricity for as long as light falls on it. Normally, when there is no smoke in the air, the light is beamed constantly between the LED and the detector. An electronic circuit (4) detects that all is well and nothing happens.  But if a fire breaks out, smoke enters the chamber and interrupts the beam. Because no light is falling on the photocell, it does not generate an electric current anymore. The circuit spots this straight away and triggers the alarm.(5).

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This type of alarm also has advantages and disadvantages.  It detects smouldering fires more quickly and is not as prone to ‘nuisance’ alarms during cooking so is less likely to be deactivated by owners and could lead to fewer deaths as a result.  It does not contain radioactive material which may make it a more appealing option for some households.  However, this kind of alarm is less quick to respond to fast flaming fires where the smoke particles are less thick so these fires could gain a firm hold before being detected.  It is also more expensive, making it a ...

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