Almost every duty in the Health and Safety at Work Act is qualified by five words: so far as is reasonably practicable. It is the difference between a standard you could never meet and one you can.
It is also widely misread as “whatever we could afford at the time”, which is close to the opposite of what it means.
The test
Reasonably practicable means what is, or was at a particular time, reasonably able to be done to ensure health and safety — having weighed up all the relevant matters. Two things follow from that wording.
It is judged at a point in time, against what was known or knowable then, not with the benefit of what the incident later revealed. And it requires weighing, which means a decision you can explain, not a conclusion you arrived at.
The matters you weigh
WorkSafe’s guidance sets out what goes into the balance:
How likely the hazard or the risk is to occur
How severe the harm could be if it did
What the person knows, or ought reasonably to know, about the risk
What the person knows, or ought reasonably to know, about the ways of eliminating or minimising it
The availability and suitability of those control measures
And last, the cost — including whether it is grossly disproportionate to the risk
Why the order matters
Cost is on the list, which surprises people who assume safety law ignores money. But it is weighed last, and only after the first five have been worked through — and the threshold is not “expensive”, it is grossly disproportionate to the risk.
That is a high bar deliberately. A control that costs real money to prevent a credible risk of serious harm is not grossly disproportionate; it is just expensive. The argument only becomes available at the margins, where the remaining risk is small and the remaining cost is enormous.
“Ought reasonably to know” is the sharp edge
Two of those matters turn on what you ought to have known, which means ignorance is not automatically a defence. If the hazard is well documented in your industry, if there is published guidance, if your trade association has written about it, if a supplier’s safety data sheet says it — you are treated as knowing.
This is the clause that catches organisations who genuinely did not know. The question is not whether you knew, but whether a reasonable business doing your kind of work should have.
What this means for your records
Because the test is about weighing, the useful evidence is the weighing itself: the hazard you identified, what you knew at the time, the options you considered, what you chose and why, and what you rejected and why.
Most organisations record the decision and lose the reasoning. Then an incident happens, and the only available account of why a control was not adopted is a recollection formed after the event. A risk register that captures the reasoning at the time is doing more work than it appears to.
Frequently asked questions
What does “so far as is reasonably practicable” mean?
What was reasonably able to be done at the time to ensure health and safety, after weighing up all relevant matters — the likelihood of the risk, the severity of the potential harm, what was known or ought to have been known about the risk and the ways of controlling it, the availability and suitability of controls, and finally cost.
Can cost be a reason not to control a risk?
Only at the margins. Cost is weighed last, and the test is whether it is grossly disproportionate to the risk — not simply whether it is expensive. A control that costs real money to prevent credible serious harm will not usually clear that bar.
Is it a defence that we did not know about the hazard?
Not necessarily. The test includes what you ought reasonably to have known. If the hazard is documented in your industry, covered by published guidance, or stated on a supplier’s safety data sheet, you are generally treated as knowing about it.
How is “reasonably practicable” judged after an incident?
Against what was known or knowable at the time the decision was made, not with hindsight. That is why recording the reasoning behind a control decision at the time is more useful than recording only the decision.
