A common misconception in safety management is that you can somehow demonstrate that you have managed something as far as is reasonably practicable; that there is some sort of clear measure. This view of managing legal obligations is often summed up in the acronym “ALARP“.
However, “reasonably practicable” is not a clear standard, it is a value judgement as described by Justice Gaudron in Silvak v Lurgi (Australia) Pty Ltd [2001] HCA 6. You do not “demonstrate” what is reasonably practicable, you mount a “reasonably practicable” argument.
Whether measures taken by an employer to manage health and safety risks in their business are “reasonably practicable” is influenced to a significant degree by the objective state of knowledge about a hazard. For example, working at heights is a well-known hazard, there are specific regulations that govern the management of working at height risks and those regulations are in turn supported by “gazetted” Codes of Practice. It would be very hard for an employer, in light of all this “knowledge” about the hazard to argue that they had done everything “reasonably practicable” if they had not applied the controls evident in the regulations and Codes of Practice.
Being objective, the test for the relevant state of knowledge does not depend on what a particular employer knew at a particular time, but rather what they “ought to have known“. Again, looking at my working at heights example, it would not be open for an individual small-business employer to argue that they did not know about the relevant risks and controls – from the Court’s perspective all employers “ought” to know about them.
The relevant state of knowledge changes over time. A good example of this over the last 20 years is our knowledge about the impact of fatigue in the workplace and the factors that can affect a worker’s level of fatigue. Whereas 15 to 20 years ago an employer may not have appreciated the cumulative effect of their workers working consecutive 12 hour shifts and driving home, the state of knowledge about fatigue risks and the development of guidance material and Codes of Practice to manage those risks mean that employers – all employers – “ought to know” about those risks and the means to control them.
The Western Australian Legislative Assembly, Education and Health Standing Committee report on The impact of FIFO work practices on mental health published today, has moved the issue of knowledge about the hazard of mental health generally, and its impact on FIFO workforces in particular, much closer to the “ought to have known” category. To borrow the Committee’s own words:
The Committee considers that the emerging evidence that shows that mental health problems may be a concern for 30 per cent of the FIFO workforce will have an important positive impact on the state of knowledge cited in section 3 of the OSH Act, and therefore on the duty of care provisions (page 51).
The Committee goes on in Finding 15 to state that the evidence will not only increase the state of knowledge, but “create duty of care responsibilities“.
In an earlier post about zero harm I made a number of observations about how the practice of safety management may undermine safety in workplaces by contributing to harm to people’s mental health and well-being. The post received a huge number of comments which unfortunately focused on the ongoing debate about the use of the term “zero harm“.
The point of the conversation, in my view is much broader.
As evidence emerges about the changing nature of workplace hazards, in particular those that impact on people’s mental health and well-being, this in turn informs our level of “knowledge“.
As our level of knowledge changes it is incumbent on the health and safety industry to turn its mind to the extent to which historical practices may cause harm.
What is it that we “ought to know” ?
My Safety Thoughts 
Could not agree with you more with regard to your observation on change over time, and this is of course where arguably one of the most important steps in the the risk management process should take place – that of “review”. In my experience this is the part that is often either overlooked or at best done sloppily. There are very few organisations that I have worked for or consulted to that do this well and diligently.