Use of Hazards Analysis in Product Engineering & Design

The safety of a product is always a core element of any product design and development process, and it is an increasingly heavily regulated area.

Ensuring that any potential hazard associated with a product’s use – either through product failure or misuse – is therefore an essential part of a product designer’s role.

The process of ensuring product and technology safety for the intended end user is called Hazards Analysis. It covers not just the direct, every day and intended use of the product, but also any possible unusual or abnormal use.

Hazards Analysis is a systematic approach which product designers use to assess and evaluate potential hazards associated with possible product failure or misuse of that product in a variety of circumstances. It extends to all situations where unintended or unforeseen loading, pressure or fatigue may come about for environmental, manufacturing, age or stress-related reasons, or simply the tool is a way to expose potential design flaws at the early stages.

Importantly, the analysis extends to an assessment of the potential severity of any harm that could arise as a result of the potential failure or misuse.

Cambridge Design Technology, amongst others, uses two tools to ensure our designs are engineered safely and with inherent quality and reliability. These are:

• Failure Mode Effects Analysis – FMEA
• Misuse Mode Effects Analysis – MMEA

Failure Mode and Effects Analysis FMEA

FMEA is the analysis of a potential single point failure of any aspect of a design and then the assessment of the possible impact of that failure.

A “failure” is defined as the loss of a function under a stated condition, in other words the possibility of a product or any of its components ceasing to work properly.

Assessing Risk using Severity & Probability

Product failure is assessed by designating a “risk priority”.

This risk is determined through a matrix of the severity of the failure and probability of the failure occurring.

Severity, in the context of a medical device, can range from ‘major’ to ‘negligible’ as follows:

• Major – May result in death or serious injury
• Moderate – May result in an injury requiring medical intervention
• Minor – May result in a non-serious injury that does not require medical intervention
• Negligible – There is no risk of injury

Probability may be assessed as follows:

• Frequent – Likely to occur frequently
• Probable – Will occur several times in the product life cycle
• Occasional – Likely to occur sometime in the lifetime of the product
• Remote – Unlikely to occur but possible to happen in the lifetime of the product
• Improbable – Unlikely to occur during the product life cycle

From the matrix of severity and probability the risk can be ascertained and would be generally classified as one of the following:

• Unacceptable
• Acceptable
• As low as reasonably practical (ALARP)

For development teams, the requirement is then to ensure that that any unacceptable risks are addressed via development, engineering, testing and scrutiny.

Any acceptable risks are mitigated by means of rational assessment of probability and severity. Changes in design or prevention through other means and detection mechanisms are implemented to ensure the product can be used safely.

In most cases, ALARP scenarios are deemed satisfactory, but it is important to note that an ALARP classification does not mean that a product failure will not occur. It does however mean that if failure does occur, no-one will be injured. While the chances of failure are slim, the possibility is nevertheless still present.

The coffee cup example

A simple example is that of a coffee cup.

This single point of failure is the handle, which may fracture and break away from the cup. The severity of the failure in this instance could be major. Boiling hot liquid could spill on to a user or someone near to the user, and could result in serious burns to at least one person.

The probability of this happening is deemed to be unlikely.

The coffee cup is a common – almost ubiquitous – product so it would not be appropriate to classify a handle failure even as occasional. To do so would suggest that every coffee cup has the potential to fail during its life time, which is clearly not the case.

From this example however, we can see how some assessment scenarios may be subjective, so it is vital that any Hazard Analysis is performed by more than one team member.

Each analysis should be reviewed and approved at different levels including at minimum:

• Technical reviewer
• Technical approver
• Senior management

Note: in the case of medical devices additional approval would also routinely be required by Regulatory Affairs, Clinical Affairs and other interested parties prior to product design specifications being released to production.

Returning to our coffee cup example, the resultant risk of a handle failure is unacceptable.

The only solution is for the design of our cup to undergo revision, engineering, testing, analysis and review. Once this has been completed, the mitigations can be made to modify the residual risk down to ALARP.

The severity remains, but the probability has to be reduced and proven to be improbable. Once the review teams agree with this, the residual risk can be revised to “acceptable”.

So far so good.

But what happens if our coffee cup is knocked or bumped in the dishwasher?

Let’s look at “misuse” mode – as distinct from the issues of “failure mode” described above.

Misuse Mode and Effects Analysis FMEA

The analysis of a misuse in product design is identical to that of failure except, as the name suggests, for the definition of the mode.

Going back to our coffee cup scenario, the misuse mode may be that the cup is thrown or slammed down in frustration by its user, who happens to be having a bad day.

All but the most ‘ruggedised’ of coffee cups are not designed to withstand this type of treatment, so this scenario is no longer “fault mode” but “misuse mode”.

Applying the same sort of analysis we used earlier, the severity of this potential scenario is moderate and the probability is remote.

The risk outcome would therefore be acceptable in this instance, however the design team and client could build some form of “mitigation action” into the product.

Examples might include product packaging warnings and ‘fair usage’ guidelines.

Cambridge Design Technology’s Experience

Cambridge Design Technology are very experienced in FMEA and MMEA processes, which can be performed on any device or product.

While the processes may at first glance appear complex and onerous, they are (for the experienced product or technology designer) straightforward when distilled into simple statements and rational assessments.

When reviewed by an approvals team, these measures will ensure that high levels of reliability, quality and safety can be inherently embedded in your product designs.

The “what if” question

Most consumer products and certainly all medical devices warrant hazards analysis at the development stage – indeed for the latter it is a mandatory requirement.

But it’s worth noting that even if your product does not require a full hazards analysis programme, the design team at Cambridge Design Technology will constantly think about every aspect of your design.

By default we look at potential hazards simply by asking the “what if” question.

What if the user does this? What if that component fails? What if…

This constant questioning and analysis is core to our product design approach, and feeds directly into the reliability, safety and quality of the designs we work on.

Can we help?

To find out more about Cambridge Design Technology and our hazards analysis services, please contact us to discuss your requirements on 01787 377106.