Bonnet and gloves OR The problem of permeation and pinholes

I wrote about growing Scotch Bonnet chilli peppers (a cultivar of Capsicum chinense) on my personal blog recently. It is quite the rigmarole to harvest and process them. It involved stinging lips, sore eyes, and coughing fits for at least an afternoon. I've got some chopped and blanched in the freezer to add into my infamous curries, but I ditched the blended chilis that I'd pickled in white wine vinegar, they smelled rank after a week or so; I must have done something wrong.

Anyway, I had got hold of some catering gloves to wear while I did the processing and put on some goggles and a face mask just for a bit of fun so that my wife (Mrs Sciencebase) could get a photo of me to illustrate the blog (and now, of course, this post). Once the post appeared and I shared it on social media, one commenter, who just happens to work at a local university of which you may have heard, mentioned a genuine problem with laboratory gloves about which not many people are aware and I thought I would discuss that a little here. I am making the assumption that readers often need to handle hazardous materials and that they have safety gloves to hand, as it were, when they do so.

One aspect of laboratory and catering gloves is that many of these disposable items are very thin and the permeation time of a hazardous substance with which they might come into contact particular if splashed can be problematic for the wearer. The common nitrile disposable gloves are good for some things but not others because of these issues. For example, such disposable gloves are a convenient way of keeping fingerprints off delicate devices when they are being made in the research laboratory. In catering, they reduce the spread of pathogens.

Under some conditions, they provide reasonable protection. In other circumstances, they can disintegrate or at best become quite permeable to some materials rather more quickly than you might wish if you're handling corrosive or toxic materials or have particularly susceptible skin. Some chemicals do not pass through gloves even after an hour or so of exposure while other substances can permeate within a few minutes. Dilute acids and alcohols are fine with nitrile, but chlorinated solvents and amines go through much more easily because of the way they get between the polymer molecules. Very thin gloves are more susceptible, obviously. For longer exposure, it is best not to risk their use with some hazardous materials that you really don't want to risk getting on your skin.

Add to that the statistics of finding a small pinhole in a glove. It is expensive to test every single item and might be a destructive thing to do anyway. So manufacturers and regulators take samples, draw conclusions about quality, and make decisions about balancing costs with price and with legal requirements. Reasonably good quality disposable plastic gloves [to standard EN 374] have a small pinhole in 65 out of 10,000. A box of 100 could conceivably have one or two such gloves and the mathematics of small samples would mean that is acceptable if that is all that you were able to test. Compare that standard to condoms where typically there are holes in about 25 in every 10000 items!

The take-home message from all this safety glove talk is that some chemicals permeate quickly and that is one important consideration. But, more worrying is the likelihood, in a busy lab with a high glove turnover, of playing "rubber glove roulette" and finding that your glove has a pinhole at the most chemically inopportune moment. If there is a reason you do not want a particular chemical or biological agent, to come into contact with your skin, then you cannot simply rely on thin safety gloves. It is seriously advisable to either double-glove and hope that any pinholes are in different gloves or not in the same place if two gloves are damaged. A slightly better option that might be more cumbersome for some applications is to use composite design or thicker gloves. Alternatively, there is also the protocol approach - find a better technique for manipulating the hazardous materials with which you work, without literally manipulating them, gloved or ungloved.

My blog commenter at the University sent me details of the various Acceptable Quality Levels (AQLs) which are essentially water tightness and air tightness of safety gloves. He also sent me a hefty list of the chemicals that one might wish to be protected against and how these couple with the permeation times and the pinholes statistics. It makes for a worrying read and makes me thankful sometimes to be desk-bound rather than bench-bound. Indeed, the only real-time chemistry I do these days is cookery although even that with the choking fumes of Scotch Bonnets and the under-fingernail risks of pith and juice are not something to be taken lightly, hence my gloves, goggles, and face mask. I think next year, I'll stick to growing tomatoes (Solanum lycopersicum cerasiforme).

David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase. His popular science book Deceived Wisdom is now available.