Edition #4 - The Role of Fail-Safe Design in Preventing Product Injuries

Good design plays a critical role in reducing product risks, especially the risk of injury. Injuries don’t just affect users; they can also trigger product recalls, legal action, and reputational damage. The EU Safety Gate 2023 Annual Report highlighted that injuries were the second most common reason for product recalls (after chemical risks), accounting for 21% of all cases.

While thorough risk assessments are essential, applying sound design principles from the outset can significantly reduce the chance of mechanical failure and resulting harm. One powerful approach is fail-safe design.

The Principle of Fail-Safe Design

Fail-safe design ensures that when a component or a product fails, it does not create a hazardous situation. Ideally, failure should make the product unusable--not dangerous.

There are a number of key ideas behind this principle:

1. The first point of failure should not lead to harm.
As a product nears the end of its usable life, the most likely failure point should not expose the user to risk. Instead, it should make the product unusable in a way that clearly signals it has reached the end of its life.

This is also particularly important in the context of product repairability, which is being actively encouraged (and regulated) through frameworks such as the EU Ecodesign Directive. Repairable products must be designed so that replacing a single part doesn’t lead to a subsequent, more dangerous failure at a later time. Refurbishment (the preferred activity for a product nearing the end of its life) should include assessment of all high-risk components, not just the visibly damaged ones.

2. Failure of multi-state components should default to a safe state.
For systems with multiple states (for example on or off), like brakes or latches, failure should result in the safest configuration being locked in. Brakes, for example, in most instances, should fail in the "on" position. While this may be frustrating for a user, this ensures a product without a working brake system cannot be used. A product where the brake fails in the off position may be continued to be used until the situation presents itself where engaging the brake is necessary to prevent an injury or other harm.  A quick-release wheel for example should fail by staying secured (inconvenient but not hazardous), not falling off mid-use.

When designing a product with different states, go through each use state and identify whether a failure could freeze a component in an unsafe state as this is a very common cause of subsequent injuries.

3. Failures must be visible.
Users must be able to recognise when something is wrong. Subtle or hidden failures are especially dangerous, as users may continue to use a product that is no longer safe.

A good design might include a secondary mechanism that prevents total collapse of a product while clearly showing the product is no longer safe to use through its partial change in geometry. A bad design hides the failure until injury occurs.

4. Avoid secondary hazards.
A failure should not create new dangers such as sharp edges, exposed moving parts, or pinch points. Unfortunately, many users will continue to use damaged products—and I’ve seen cases where this led to crushed fingers or worse. Design with this reality in mind.

Tip: Durability testing is a valuable tool to simulate long-term wear and identify likely failure points and hazards created as a result of failure. It can help you build safer end-of-life scenarios into your design.

By integrating fail-safe principles into product design from the start, businesses can significantly reduce injury risks, meet regulatory expectations, and create safer, more reliable products.

In the next newsletter we will look at safety mechanism design best practice.