Product Safety Hierarchy: PWC Manufacturers Must Design Risk Out of PWC Rather Than Simply Warning of Risk


Disputes over warnings almost always bleed over into disputes over product design. And despite both being mechanisms for controlling product hazards and promoting safety, warning and design represent polar extremes in viewpoints on responsibility, blame and legal interests. Under the design approach, the product manufacturer/designer bears the responsibility for product safety. On the other hand, the warning approach places responsibility for the product’s safety onto the user (by requiring action/inaction on the part of the user to address safety hazards arising from design flaws that could have been designed out of the product).

Design and warnings both have advantages and disadvantages. The major advantage of warnings is that they are relatively cheap, so naturally product manufacturers prefer them. This is fine, since there is no denying that practical considerations always play a role in safety, as in everything else. However, warnings also have a major down-side; they are highly unreliable. Research has repeatedly shown, that outside the artificial world of university laboratories, warnings frequently (and some would say usually) fail.

Design costs more but has the advantage of being, in principle, a more certain means for preventing accidents. Human factors professionals widely recognize the unreliability of warnings and superiority of design. This is illustrated by the various safety protocols that human factors and ergonomic professionals employ. The most common is referred to as the “Safety Hierarchy”:

“Safety Hierarchy”

1 Design
2. Guard
3. Warn

When a hazard is identified, the safest approach is to perform a redesign which removes the hazard. If redesign is not feasible, then the next best approach is to employ a guard or barrier to separate the user from the hazard. If the guard is not feasible, then the next step is to use a warning. Use of the Safety Hierarchy is standard safety practice.

Despite slight industry-specific variations in the safety hierarchy, all are based on the premise that warnings and other methods that depend on user behavior are inferior compared to design changes that eliminate the hazard or guard against the hazard. Safety mechanisms can be classified based upon their reliance on user behavior, as follows (note that the order is also the order of effectiveness):

  • No dependence on user behavior – Design changes which provide complete separation of the user from the hazard;
  • Partial dependence on user behavior – Guards that are not complete or tamper-proof. In some cases, users can circumvent guards, forget to use them or actively attempt to defeat them, i.e., disabling a lockout;
  • Complete dependence on user behavior – Warnings, training, procedures and protective clothing.

Why does the effectiveness of a safety mechanism decline upon increased reliance on user behavior? The reasons are both numerous and varied: People become tired and distracted. They work under pressure to get the job done. They know that warnings are often for legal “cover-your-ass” purposes rather than safety ones. They see everyone else ignoring the warning or not following procedures with no bad consequences. They believe that they can control the risk, or they believe that there is no risk.

Application of the Safety Hierarchy to the PWC Industry

As addressed in a previous blog entry, the inadequacy of using only a warning remedy for the hazard of rear ejection orifice injuries is, or should be, apparent to personal watercraft manufacturers. Compliance with a warning to wear a wetsuit or a wetsuit bottom when riding as a passenger on a PWC would be predictably and reasonably low in light of various factors reliably shown in human factors research to affect compliance with product warnings: perception of risk, cost of compliance, and the tendency to emulate others.

Perception of risk. Perception of risk for operating or riding on personal watercraft is lower than the risks associated with the use of other motorized recreational vehicles. Research has also shown that the risk perception for riding as a passenger on a personal watercraft was exceptionally low and not reliably different from numerous low-risk activities such as riding in a small private plane or talking on a home telephone during a thunderstorm. Low perception of risk decreases compliance with warnings.

Cost of compliance. A common difficulty in producing compliance with warnings is the cost of compliance. A variety of studies have shown that the cost of compliance affects the use of safety equipment. For a person simply wanting to ride as a passenger on a PWC and having no access to a wetsuit or wetsuit bottom, the cost of compliance in obtaining one would, almost always, be enormous. Many times riding as a passenger on a PWC is often not a planned event, but the opportunity to do so is taken when it is available. Very seldom will the operator or owner of a PWC, who offers a ride, have available a wetsuit, a wetsuit bottom, or some other item of protective clothing. High costs of compliance decrease compliance with warnings.

Tendency to emulate others. A variety of studies in human factors have found that compliance with warnings is reduced by observing others in the situation who do not comply. Research shows that the use of wetsuits, wet suit bottoms, or neoprene shorts when riding as passengers on personal watercraft is practically nonexistent. That research to date involves the observations of over 300 PWC users in seven states during the summer months of 2004. Wet suits, wet suit bottoms, or neoprene shorts were worn by only 4% of operators and by only 1% of passengers. Almost all operators and passengers on PWCs wore only swimsuits.

Bottom line – If PWC manufacturers really cared about safety as they profess to, they would manufacture personal watercraft in accordance with the safety hierarchy, and incorporate design changes into PWC that would prevent orifice injuries, rather than simply providing a warning that such injuries can occur.


Green, M. (2006). Safety Hierarchy: Design v. Warnings.

Arndt, S., Ayres, T., McCarthy, R., Schmidt, R., Wood, C. & Young ,D. (1998). Warning Labels and Accident Data. Human Factors and Ergonomics Society Annual Meeting Proceedings, 550-553.

Ayres, T. (2004). Facing a pervasive bias in warnings research. Human Factors and Ergonomics Society Annual Meeting Proceedings, 28, 2035-2039.

Ayres, T., Wood, C., Schmidt, R., & McCarthy, R. (1998). Risk perception and behavioral choice. International Journal of Cognitive Ergonomics, 2, 35-52).

Ayres, T., Wood, C, Schmidt, R., Young, D. & Murray, J. (1998). Effectiveness of Warning Labels and Signs: An Update on Compliance Research. Proceedings of the Silicon Valley Ergonomics Conference & Exposition, 199-205.

Brauer, R. (2006) Safety And Health For Engineers. John Wiley & Sons, Inc: Hoboken, New Jersey.

Geller, E (2000). The Psychology of Safety Handbook. Lewis Publishers Inc.

Hale, A. & Glendon, I. (1987). Individual Behaviour in the Face of Danger.

Manuele, J. (2003). On The Practice of Safety. John Wiley & Sons, Inc: Hoboken, New Jersey.

McCarthy, R, Finnegan, J., Krumm-Scott, S., McCarthy, G. (1984) Product information presentation, user behavior, and safety. Human Factors and Ergonomics Society Annual Meeting Proceedings, 81-85.

Reason J. (2000) Human error: models and management. British Medical Journal, 320, 768-770.

Stephans, R. (2004). System Safety For the 21st Century. The Updated And Revised Edition Of System Safety 2000. John Wiley & Sons, Inc: Hoboken, New Jersey.

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