A very common conversation I have with organisations is, what is “practicable” and how do organisations meet the legal obligation to manage hazards “as low as” or “so far as is” practicable? Organisations often tell me this very difficult because “risk”, or risk perception, is “subjective”. What I see as being hazardous or risky, is different from how someone else might see it.
I think this is true, and personal perceptions of hazard and risk do vary based on our personal understanding.
It is, however, a very different thing to extrapolate that thinking into health and safety legislation and conclude that practicable is somehow subjective. It is not. Your view of what is practicable is not conclusive - it is judged against objective evidence.
At first glance, this may seem counterintuitive. After all, the High Court has said that practicable is a “value judgement”:
The words “reasonably practicable” have, somewhat surprisingly, been the subject of much judicial consideration. It is surprising because the word “reasonably practicable” are ordinary words bearing their ordinary meaning. And the question whether a measure is or is not reasonably practicable is one which requires no more than the making of a value judgement in light of all the facts. (per Gaudron J, Slivak v Lurgi (Aust) Pty Ltd 177 ALR 585 )
Even though safety can be defined as a value judgement, it is not subjective.
If I say I do not like spinach, that is my subjective view of the vegetable. Someone else might like spinach. But there are no objective criteria about whether spinach is good or bad. However, if I send a worker onto a roof without fall protection a Court can, and will, make an objective assessment about whether I have managed the risk as far as reasonably practicable.
Whether a measure could, or should, have been taken in a particular case is an objective assessment that has to be tested against the general state of knowledge about that risk, as well as any specific knowledge that was available within a relevant industry (See for example, Chugg v Pacific Dunlop (No 2)  3 VR 934; Yamasa Seafood Australia Pty Ltd v Watkins  VSC 156; Silent Vector v Shepherd  WASCA 315).
An organisation or an individual is not entitled to rely on their subjective view of the world or subjective state of knowledge to justify their actions or inaction in relation to safety. An organisation or an individual cannot just say they did not know about a hazard or relevant control in arguing they did everything practicable. The fact and organisation or individual did not foresee the hazard or understand the controls may be relevant to whether or not it was foreseeable, but it will not be conclusive (R v Australian Char Pty Ltd  3 VR 834).
To take my working on the roof example above, an organisation is not entitled to say they were not aware of codes of practice relevant to working at height – any reasonable organisation engaged in working on a roof would be expected to understand, know about and implement the relevant codes of practice.
The legal test is what the organisation or individual knew, or ought to have known relative to the hazard. What would a reasonable organisational individual in the same circumstances have known or done? This is an objective test, independent of the individual circumstances or knowledge of the particular business or individual.
The relevant state of knowledge is not that of the particular employer who is the defendant, but what is generally known, to which, upon reasonable inquiry, the employer might have gained access. (Kirwin v Laing O’Rourke (BMC) Pty Ltd  WASC 194, . See also R v Australian Char Pty Ltd  3 VR 834; Reilly v Devcon Australia Pty Ltd  WASCA 84)
I think the greater confusion in most cases is finding the balance between what is practicable and doing everything possible. Employers are not required to ensure that accidents never happen. The obligation is to provide and maintain, so far as is reasonably practicable, a working environment that is safe and without risks to health (See for example: Holmes v RE Spence & Co Pty Ltd (1992) 5 VIR 119; R v Australian Char Pty Ltd  3 VR 834; R v Commercial Industrial Construction Group (2006) 14 VR 321; Western Power Corporation v Shepherd  WASCA 233; Baiada Poultry Pty Ltd v R  HCA 14).
All the law is saying, is that sometimes you can do everything reasonably practicable, but accidents still happen.
This article represents a general discussion about legal principles. It is not specific advice, and you should seek your own legal advice in relation to your specific circumstances.