Production tests aren't just for quality control

Oct. 20, 2005
Design engineers sometimes think only about end use when the topic of product safety comes up.

Big mistake: Design-for-safety must anticipate what can happen to the product during production. If production strays from design tolerances, poor quality may be the least of the problems. We've seen instances where out-of-tolerance conditions rendered parts unsafe.

For example, one manufacturer of gas valves fielded units containing a riser and casting. The user had to pull the dial out to clear the riser when turning the dial to the on position. This action then activated the pilot light's thermocouple monitor. This guard was there to turn the gas line off in case the pilot light went out.

But a flaw developed during production. The riser ended up being so low that users could force the dial to the on position. This flaw also left the gas line under the thermostat's control. So when the thermostat was set to heat, gas went to the furnace even when the pilot light was out.

The result: Over time, propane gas leaked into basements. Several gas explosions and fires happened this way. The Consumer Product Safety Commission demanded that the manufacturer recall the valves.

Though it may sound obvious, communication among manufacturing, design, quality-assurance and field-service personnel can help avert such disasters. Manufacturing processes should jibe with the latest design drawings. Design changes must go through a formal engineering change request process before there are any modifications in manufacturing. If a part could affect product safety, there should be at least one sign-off from a product-safety person to ensure design changes don't introduce new safety hazards.

All safety-related components and parts, especially those from outside suppliers, should be monitored. Product-safety personnel should review test results. When possible, purchase orders and sales contracts should contain indemnification clauses assigning vendors and subcontractors liability for their products and their performance. If there is an injury because of a faulty component, liability may be passed on to the vendor supplying the component.

Manufacturers must identify all components whose failure could pose safety hazards. Those components and all final products that carry a significant injury risk should be tracked all the way through manufacturing and distribution.

Inspections and tests throughout production can prove that products met their design specification and can show products contain no defects or hazards. Of course, safety-related features, warnings, and instructions should be checked at final assembly.

If worse comes to worst, most states now let manufacturers claim alterations or modifications as a legal defense. To use this defense, a manufacturer must present evidence that warnings, instructions, guards, and all other safety features were in place when the product left the manufacturer's control. In this regard, the responsibility for final product inspection usually should not be delegated to dealers and distributors.

Similarly, packaging must not only be safe, it must protect product handlers, shippers, and bystanders from unsafe conditions. A manufacturer can be held liable for product defects that result from inadequate packaging.

Lanny Berke is a registered professional engineer and a Certified Safety Professional involved in forensic engineering since 1972. Got a question about safety? You can reach Lanny at [email protected]

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