Continuing our discussion from last week, here's more on the topic of minumum standards from the President of CIC:
So why would a rubber curing oven explode despite being fitted with an analyzer in the drying zone?
Everything appeared to be correct. The design specifications given to the machine maker called for a low Flash Point solvent. The drying zone wasn’t particularly hot. The analyzer was in the right place in the drying zone. It should have been OK. The thing is, treating rubber involves two main types of solvents, not just one, something the machine maker didn’t realize and the end user didn’t think important to talk about. The one specified was indeed easily dried and had a low Flash Point. The other was quite a bit harder to dry, with a Flash Point well above the temperature of the drying zone. So when the end user switched between the two solvents, thinking nothing of it – just normal rubber treating - the high Flash Point solvent went right past the drying zone without producing any fumes worth measuring and carried into the curing zone heated well above the Boiling Point, where it exploded.
The “spill-over” or “profile shift” of solvent between adjacent drying zones is why an analyzer in the main drying zone if often insufficient to detect problems with drying. The main drying zone is often the highest reading normally, but often the adjacent zone is where the highest concentration occurs during an upset that floods the dryer with solvent.