Pete
While the question you asked was simple, 'how is that initial judgement being quantified?, both your own comments and those of Ray are, not unreasonably much more expansive.
This is normal and unavoidable. If you read research by leading experts on risk management, such as Fischoff, you can see that the leading edge of the debate is about the cognitive psychology of risks, i.e. how can human minds conceptualise uncertainties and communicate about it.
Translating this into operational aspects of safety and health management, I agree with Ray's observation about the probable pace of change in complex organisations (and even in very small ones). In my experience, the greatest difficulty is not about the processes of quantification but about how people at work. especially at managerial level, address human emotions, which are unavoidably part of what every person brings to work.
Emotions, of their nature, can be quantified with much less reliability and validity than other aspects of human behaviour and experience. This is one reason why the safety profession is unwilling or unable to manage them or even acknowledge them with greater skill and clarity.
A simple example may illustrate. At the 2010 IOSH Railway SIG conference, none of the many railway managers who spoke about managing people said one single word about emotions. When Dave Morris, former Chief Inspector of the RR and current chairman of NEBOSH spoke about the culture of railway safety, he referred to the importance of communications and occupational health, insisting that both 'must be greatly improved!'. When I enquired how they could be improved when even he made no mention of emotions, he visibly gulped and, after a lengthy pause, said 'I have great difficulty dealing with grief!'.
As long as senior management see 'grief' as the only emotion associated with safety and with effective performance, the safety profession has a very, very long journey into not only managing 'risks' but also of consistently effective and profitabe performance.
To my knowledge, no professions are very effectively and consistently led, by men (or women) with such outdated beliefs about the people for whose safety, health and performance they are responsible. If you want to read relevant research, look at 'From Good to Great' by Jim Collins (Harper, 1998) and at 'Risky Business', ed. R Burke and C Cooper, Gower, 2010