Roger Searjeant (rogers(at)i2.co.uk)
Fri, 20 Nov 1998 16:05:07 -0000
A fundamental point behind the ALARP principle is allowing (justified) flexibility in meeting safety objectives. We can't expect to ('across the board' define what is acceptable. Even the ALARP principle when encoded in company procedures does not provide a mechanistic interpretation of when things are OK vs. when things are not OK. ALARP is by its nature subjective. Subjectivity in safety decisions is nothing new - people make subjective judgements all the time. ALARP simply brings this process out into the open and forces people to justify (usually through the medium of the safety case) their decisions. [Roger] OK, that almost answers my question; as long as a Safety Case has been made for the system in question, and the judgements made (about what is acceptable or reasonable) are recorded in it, there is something to refer to later. Whether a risk has been reduced ALARP requires study and evaluation of the justification of risk reduction measures employed vs. not employed, cost of these options etc. It is not a tick / cross exercise. Apart from having limits (the boundary in the ALARP triangle between TOLERABLE and INTOLERABLE risk) ACCEPTABLE risk cannot be determined a priori. [Roger] I can see that this sort of thing cannot be a tick/cross exercise. What I am trying to understand is how the Safety Case arguments are reviewed/approved before implementation, and examined (perhaps in the light of an accident) after implementation. When you are engaged in a project requiring a Safety Case, how do you know whether the case you are constructing will stand up to scrutiny? Is it mostly (or solely) a matter of 'prior art', looking at past cases to see how they were written? Are there guidelines for constructing a Safety Case (in a given field)? As an interested newcomer to this field, I am bound to ask elementary questions. Examples would help. Are there any Safety Cases published on the web? Would they be digestible/understandable? If not, is there other material available? Thanks, Roger Searjeant. Attachment Converted: "C:\JDMDATA\ZImports\RE Public domain examples of t1"