The Rules of Safe Product Design

The first challenge for a lawyer listening to a client’s description of a possible case is to answer the question, “How did the product contribute to the injury?”

The two cases described below, both involving electrical defects, demonstrate the utility of the rules of safe design as a starting point in understanding a products case.

I. Introduction

Legal analysis of a products case is premature and not useful until someone first figures out what happened. When a client comes into a lawyer’s office having been injured by a possibly defective product, the best way to think about the case – and understand its strengths – is to consider the client’s experience in light of the rules used by engineers for analyzing safe product design. Other approaches, such as thinking about negligence, warranty and strict liability, may be more instinctual for lawyers, or may arise more naturally from hornbooks (which often discuss products cases in terms of manufacturing v. design v. warnings defects).

However correct, legal analysis of a products case is premature and not useful until someone first figures out what happened. The first challenge for a lawyer listening to a client’s description of a possible case is to answer the question, “How did the product contribute to the injury?”

The two cases described below, both involving electrical defects, demonstrate the utility of the rules of safe design as a starting point in understanding a products case.

Safe Product Design

The fundamental rules of safety in product design are the following:

Eliminate foreseeable danger wherever possible by designing the danger out of the product;

If it is not possible to design danger out of the product, guard the user against it;

Where it is not possible to either design the danger out or guard against it, give warnings and instructions so the product can be used safely.

These design safety rules apply to all products, from those with no moving parts (such as one-piece dolls, baking dishes, hammers, knives and grinding wheels) to complex systems powered mechanically, chemically, pneumatically, hydraulically and electrically.

II. The Toaster

On a summer morning in York County, a woman was cleaning her kitchen after breakfast. Within the past month, she had purchased a new toaster. After removing the crumb tray (which comes all the way out from the body of the toaster), she wiped everything down and started to put the crumb try back into the toaster. As she did so, she failed to think about two things. First, she had forgotten to unplug the toaster. Second, she was holding the crumb tray upside down.

As the woman cradled the toaster in her left arm, and slid the crumb tray, still upside down, into the toaster with her right hand, current pulsed through her arms and body. Her muscles went into spasm with enough force to break both bones in both of her forearms. Unable to release her grasp on the toaster, she eventually fell over, pulling the toaster’s plug out of the wall in the process. She was found on the kitchen floor by her grandson, alive but unconscious.

How did the toaster contribute to this injury?

To find the answer, the original toaster was obtained from the client and two exemplar toasters were purchased from the same store where the client had obtained hers. An expert was retained to disassemble the client’s toaster. While disassembly creates some risk of spoliation arguments from the defense, reasonable investigation has to start somewhere.

Inside the toaster, the expert found and photographed evidence of electrical arcing, and observed that the electrical leads (where the power cord ends inside the toaster) were only a half-inch apart and not electrically insulated or guarded in any way. Furthermore, the crumb tray, which was shaped like a shallow trough, contacted the bare electrical leads when inserted upside down, closing or “shorting” the toaster’s power circuit. Once the crumb tray connected the two electrical leads, it and the body of the toaster became electrified just as if they were directly plugged into the wall.

The foreseeable danger inherent in the toaster is the obvious danger of electrical shock. Since this danger cannot be completely designed out of the toaster, the rules of safe product design require that the manufacturer guard against it. With no insulation on the electrical leads, their proximity to each other, and the risk of “shorting” them with the crumb tray, it appeared that the second rule of safe product design had been disregarded by the designer of the toaster.

Having arrived at an initial conclusion about how the toaster violated the rules of safe product design, we could then begin to think about legal issues such as strict products liability, the definition of product defect, how to prove it, how comparative fault might affect the case, etc.

Disassembly of the exemplar toasters revealed that they were built exactly like the client’s toaster, confirming that this was a case of design defect, and not a manufacturing error in a particular toaster.

For purposes of making a settlement demand, it was not hard to make the argument that shielding the electrical leads with insulation, or separating them physically, or changing the shape of the crumb tray would easily and inexpensively guard the user against the danger of electrical shock.

The case didn’t settle before suit was filed, but it settled shortly thereafter when the defendant produced design drawings showing recent modifications adding the same types of guarding plaintiff was arguing for.

III. The Hot Glue and Sealing Machine

In Lewiston, a factory worker was assigned to glue covers on calendar books using a machine that applies hot glue and seals the book and cover together with mechanical pressure of about 200 lbs. per square inch.

To load the book and cover into the machine, the worker must put his hands between the heated plates of the press. This machine uses compressed air to provide the pressing force. Electricity heats the press plates, and controls the pneumatic valves which activate the press.

The danger of having the operator’s hands mechanically crushed and burned by the press is obvious, and cannot be designed out of the machine without making it non-functional. Applying the second rule of safe product design, the press manufacturer guarded against the danger by the use of palm buttons. Palm buttons are electric switches, located a safe distance apart, which must be simultaneously activated (one by the right hand and one by the left hand) in order to cycle the press plates.

On the day of the injury, while the operator was placing a book and cover between the press plates, with his hands nowhere near the palm buttons, the press cycled, crushing and burning his hands. How could this happen with the palm buttons in place to guard against it?

The employer did an investigation which revealed the problem. Inside the electrical control box, there were bare wires leading to the valve which controlled the release of air to activate the press. The wires were very close together. Under some circumstances, including a combination of high levels of moisture in the air (moisture conducts electricity) and vibration, electrical arcing occurred across the wires. The arcing resulted in a short circuit, eliminating the role of the palm buttons and releasing air to power the machine with no warning to the operator. The arcing is what resulted in the operator’s severe injury.

The employer’s investigation answered the question of how the product contributed to the injury. Interestingly, although the primary foreseeable danger in the press (physical crushing and burning) caused the injury, it turned out not to be the center of the defect argument. The defect in the product arose from a secondary danger (electrical arcing) which was introduced into the machine by a poorly designed control system. In this case, it is most helpful to think about the defective product as the control system, not the press.

Once understood as a case about a defective control system, the case developed as a strict products liability case in which the risk/utility analysis, necessary to proving defect under the law, centered on the danger of bare wires, alternative designs that could eliminate or guard against that danger, and so on.

The manufacturer denied responsibility, asserting “intervening cause” in that the employer had modified some aspects of the electrical controls. While some modifications had been made, they were not in the electrical control box at issue.

A lawsuit was filed, and in discovery the defendant was forced to reveal other similar incidents which had occurred in control systems made according to the same design as the one at issue. The case settled shortly thereafter.

Understanding precisely how the press violated the rules of safe product design was helpful in choosing expert witnesses, framing defect arguments, anticipating defenses and drafting discovery. It allowed us to avoid being sidetracked by the endless list of legal and technical issues which can confront a plaintiff in a products case, such as the open and obvious danger of the hot press plates, the adequacy of warnings and instructions which may have come with the press.

IV. Conclusion

The basic rules of safe product design exist and are well-known to engineers because they work. Conscientiously applied, they result in better products. When the rules are ignored or forgotten, and when injury results, those same rules can be applied by lawyers to efficiently find an answer to the question of how the product contributed to the injury. Only after that question is answered can the “legal” aspects of case development begin.

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