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Machine Design

Berke on Safety: The Case of the Flaming Hair Dryer

Hair-dryer users have reported fire shooting out of the handle or the snout end of their hair dryers.

Other reports say the hair dryer “turned itself on” and started an electrical fire. It is my opinion that no one conducted a proper hazard analysis before handing consumers these devices which deliver enough energy to heat a room.

Ferreting out product hazards through accident investigations, after there has already been a serious injury or property damage, is no longer acceptable design practice. Fault Tree Analysis (FTA) and Failure Mode and Effect Analysis (FMEA) are two common proactive approaches that ask how a failure in part of the product could lead to an accident.

I prefer to use Preliminary Hazard Analysis (PHA) which asks the question: “How safe is a product when there is no failure in its systems?” PHA examines all aspects of a product, including human error, misuse, and all reasonably foreseeable events.

The PHA process consists of a brainstorming phase, an evaluation phase, and a corrective action phase. Even simple analyses often require two or more iterations of these phases.

This might seem like overkill for a simple consumer device. But when a product is put under the microscope during a hazard analysis, designers often find ways to improve the way the product meets customer needs and wants. The examination may also reveal ways to reduce cost or improve reliability.

To illustrate this process, let’s consider the familiar hair dryer.

The hair-dryer brainstorming team should include experts in various disciplines who were not involved in designing the product. Product designers could become defensive when they are told their “child,” the project they have been working on for the last six to 12 months, is flawed. The team should be able to examine the hair dryer or at least a sketch, model, or prototype.

The brainstorming team for this project should include a safety professional, a product designer, a human-factors specialist, an electrical engineer, a hair-dryer marketing professional, and a scribe. The safety professional will probably moderate the brainstorming session, keeping the ideas flowing and deciding when to wrap up.

The scribe will write down all the ideas the team blurts out. At this point, no one should judge the ideas that are generated. One or two ridiculous pronouncements might trigger some very good ideas from other members of the team. Our imaginary brainstorming session sounded like this:

“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.” “Your hair can get caught in the air intake.”

You will probably come up with more the next time someone in your home uses a hair dryer. Post your brainstorming ideas in the General Engineering Discussion forum at

Next month, our hair-dryer team will evaluate the brainstorming ideas and turn them into concrete corrective actions.

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