Risk, society and design standards

Risk is the combination of the probability that a hazard causes harm and the severity of that harm: $\text{Risk} = \text{probability} \times \text{consequence}$. Zero risk is impossible, so designers aim for risk that is as low as reasonably practicable (ALARP).

Risk and society

• People accept voluntary risks (driving, climbing) more easily than involuntary ones (a dam or chemical plant nearby).
• Rare events with large consequences (aircraft crash, bridge collapse) are feared more than common small ones, though total harm may be less.
• Acceptance depends on benefit, familiarity, control and trust. Engineers have an ethical duty to protect public safety, health and welfare before cost.

Regulations and standards

• Regulations/laws are legally binding (safety acts, boiler, pressure vessel and lift rules, building codes).
• Standards and codes (ISO, IEC, ASME, IS, NS) give accepted minimum design rules, factors of safety, test methods and dimensions; following them also helps in liability defence.
• Product liability puts responsibility on the designer and maker for defects and missing warnings.

Risk assessment steps

1. Define the machine limits, use and misuse.
2. Identify hazards (crushing, shearing, entanglement, high pressure, noise).
3. Estimate risk: likelihood (exposure, probability of event, chance to avoid) and severity.
4. Evaluate against criteria: acceptable or not.
5. Reduce risk in order: eliminate by design, use guards and protective devices, then warnings and training, then personal protective equipment.
6. Document, review and repeat after any change.