Basis of Safety

When someone asks “what is your basis of safety?”, in an engineering context, how would you reply?

The concept of a “basis of safety” can be hard to explain, and even harder to prove in some cases.

It is certainly a document you should consider during the design phase as it will then steer and inform future design decisions.

In the most basic terms and to comply with various legislative requirements, our clients have to demonstrate that they are keeping personnel safe, in line with ALARP principles.

To do this, they need to identify HOW people will be kept safe, by demonstrating HOW they are keeping them safe, e.g. how a fire or explosion will be prevented or mitigated.

We therefore describe there being two types of basis of safety we can use:

Preventative basis of safety

1. Avoidance of a flammable atmosphere e.g. by inertion, high ventilation, using an alternative material, making the material non flammable etc.
2. Avoidance of ignition sources harder than it sounds when there are so many to consider
3. Control of ignition sources which easier to do, by e.g. using suitably rated equipment which should not become an ignition sources if maintained and operated correctly.

Mitigative basis of safety

1. Safe venting of explosions (to a safe location, or with safe venting equipment such as flameless vents)
2. Explosion suppression (potentially expensive and complex solution)
3. Exclusion of personnel from the area (this could be hard to prove).
4. Once the most suitable basis of safety has been chosen, then all the safeguards needed to achieve this need to be in place.

This is where recommendations come in. If there are gaps in protection layers which means a basis of safety has not been achieved to an ALARP level, then we can make recommendations to plug these gaps with improvements.

For example, if we have a dust collector, with an explosion panel fitted, and the intended basis of safety is “safe venting of explosions”, there might need to be a recommendation to:

Ensure explosion panel is suitably ATEX rated and maintained.

Ensure explosion panel does not vent into an occupied area.

The equipment may already have the means to provide the basis of safety, but it may not quite be there in terms of a reliable and ALARP level.
So next time someone asks what your basis of safety is going to be, just think “should we preventing this, or mitigating this?”.

This is why completing the basis of safety should be an early priority. In line with the risk hierarchy and principals of inherently safe design, preventative is always preferrable, and is most likely to achieve before a new process or site has been built.

Contact Owen Llanwarne to find out how to integrate BoS in to your design and operations.