JBD wrote:
PaulEngr wrote:
Sounds like yet another rumor started somewhere.
Most likely from the old rumor that UV light from a welding arc would also cause contacts to stick, or fuse, to the eyeball.
It seems many safety people have a hard time with the concept of probable vs possible, to the point I wonder how many lottery tickets they buy.
Probabilistic safety is pretty much where the modern safety approach has gone to. I work in maintenance. Do you know how many times I've been asked the question can you guarantee X? To which the standard reply is there are no guarantees in life.
Realistically the modern approach is two fold. First we ignore all the safeties that change the probability of an outcome or in some cases even those (passive protections) and then we apply all the safeties and estimate likelihood. Then based on these two factors we look at whether or not the risk (combination of likelihood AND magnitude) are acceptable or not. Generally the goal is to achieve a likelihood of one in a million (per year) or less often of a single fatality which is generally where shock hazards are. As we ratchet back from that outcome we can gradually accept higher likelihoods for lesser injuries. For instance a hospital stay might be 1 in 100,000 which is where arc flash is, all the way up to paper cuts.
However there are to caveats that make this hard. First off a lot of safety folks struggle with the two factor approach and constantly try to lump things together. They get a god complex and believe they are alone in a crusade to save the world from themselves, and will stop at nothing to achieve it. They get hung up on the morbid side and ignore the rest. The second and more severe problem is the Ethics Code for professional engineers that specifically calls for taking a "conservative approach" to everything. So they turn their brains off and view everything from an extreme absolutist point of view regardless of the consequences. In electrical engineering this is understandable. Generally it is fairly easy and inexpensive to beef up the structure to achieve a higher AIC, use a bigger breaker, etc. But in other engineering fields particularly the "soft" types such as materials engineering, chemical engineering, and the like, this "bigger hammer" doesn't work. At one time both were declared chicken littles and ignored but in today's litigious environment this approach actually gets credibility.