“You could drop it into water.” “You could drop it on the floor and crack the plastic housing.”
“The plastic housing can overheat.” “The hot air makes your hair frizzy.” “Ha! The hot air can burn your skin, too.”
These were some of the ideas brainstormed in my last column (Machine Design, Apr. 24) as we walked through the preliminary-hazard analysis (PHA) for the common hair drier. The next step is evaluation of the brainstormed ideas.
The team will decide how probable each event is, how serious the injury or property damage could be, and how each hazard should be addressed. They may choose to do nothing, to redesign around the problem, to guard against the hazard, to warn the user of the hazard, or to keep the product out of the marketplace altogether.
The design team was excluded from the judgment-free brainstorming session, but now they should be available to answer questions and to take on the recommended fixes. Our hair-dryer evaluation might proceed as follows:
The first item on our list, dropping the unit in water, has already been addressed by the industry. Ground-fault circuit interrupters (GFCI) at the plug end of the electric cord guard the user against electric shock. I have not heard of any electric-shock deaths since GFCIs were implemented.
The team should go through a second PHA iteration after the corrective measures have been implemented; fixes often create or uncover additional hazards. In the case of the GFCI, a second round might have revealed that the electric-cord insulation can break down where the cord meets the GFCI plug and the strain relief at the hair-dryer’s handle. Without the insulation’s support, the copper wire can fracture at both ends of the cord. Arcing at the break in the copper wire may create high heat and cause fires.
Consumers have claimed that their hair dryers turn themselves on and start a fire. I believe power is cut to the hair-dryer motor when the copper wire breaks. The operator, unsure of why the dryer stopped, sets the unit down and walks away without unplugging it. Over time, the wire relaxes, the two broken ends come together, and an arc leads to the reported fire.
Many users have sent the Consumer Product Safety Commission (CPSC) photos showing this copper-wire failure. In some cases, they have included the hair dryers themselves with their letters of complaint. These complaints are just the tip of the iceberg. It is only a matter of time before the CPSC forces a recall. Then we will really see the sparks fly.
Lanny Berke is a registered professional engineer and certified safety professional involved in forensic engineering since 1972. Got a question about safety? You can reach Lanny at firstname.lastname@example.org.