Keeping it Safe

The basic idea behind hair dryers is pretty simple, but producing one for mass consumption requires some hard thinking about safety features. Manufacturers have to predict how their hair dryer might be misused. They then try to design a product that will be safe in the widest variety of conditions.

Some common safety features of hair dryers are:

A bimetallic switch that prevents overheating

• A safety cut-off switch - Your scalp can be burned by temperatures more than 140 degrees Fahrenheit (approximately 60 degrees Celsius). To ensure that the air coming out of the barrel never nears this temperature, hair dryers have some type of heat sensor that trips the circuit and shuts off the motor when the temperature rises too much. This hair dryer and many others rely on a simple bimetallic strip as a cut off switch.

  A bimetallic switch is made out of sheets of two metals. Both metals expand when heated, but at different rates. When the temperature rises inside the hair dryer, the strip heats up and bends because one metal sheet has grown larger than the other. When it reaches a certain point, it trips a switch that cuts off power to the hair dryer. (For more information on bimetallic strips, see How Thermometers Work).

• A thermal fuse - For further protection against overheating and catching fire, there is often a thermal fuse included in the heating element circuit. This fuse will blow and break the circuit if the temperature and current are excessively high.

• Insulation - Without proper insulation, the outside of the hair dryer would become extremely hot to the touch. If you grabbed it by the barrel after using it, it might seriously burn your hand! To prevent this, this hair dryer has a heat shield of insulating material that lines the plastic barrel.

  The heat shield keeps the barrel of the hair dryer from becoming too hot.

  The side screens and front grill keep unwanted objects from getting inside the hair dryer.

• Protective screens - When air is drawn into the hair dryer as the fan blades turn, other things outside the hair dryer are also pulled toward the air intake. This is why you'll find a wire screen covering the air holes on either side of the dryer. After you've used a hair dryer for a while, you'll find a large amount of lint building up on the outside of the screen. If this were to built up inside the hair dryer, it would be scorched by the heating element or might even clog the motor itself.

  Even with this screen in place, you'll need to periodically pick lint off the screen. Too much lint can block the airflow into the dryer, and the hair dryer will overheat with less air carrying away the heat generated by the nichrome coil. Newer hair dryers have incorporated some technology from the clothes dryer: a removable lint screen that's easier to clean.

• Front grill - The end of the barrel of a hair dryer is covered by a grill made out of material that can withstand the heat coming from the dryer. This screen makes it difficult for small children, or other especially inquisitive people, to stick their fingers or other objects down the barrel of the dryer, where they could be burned by contact with the heating element.

  A GFCI has circuit interrupters that cut off power to the dryer at the outlet should the dryer be dropped in water while it's plugged in.

• Ground Fault Circuit Interrupt (GFCI) - Since 1991, all portable hair dryers have been required by federal law to protect you against electrocution should you accidentally drop one in water while it's plugged in. This applies whether the hair dryer is on or off. A GFCI is the larger, polarized plug that you'll find on many consumer appliances. When they are plugged in, GFCIs monitor the amount of current that is running from one slot of a wall outlet through an electric circuit and back to the other slot. If they sense a leak in the current, they trip the circuit. (See How does a GFCI outlet work? for details).

What happens to a hair dryer if you drop it in water when it's not plugged in? You don't run the risk of electrocution, since there is no source of current, but you can certainly damage the hair dryer if all its components get wet. So, plugged in or not, it's a bad idea to throw it in the tub.