Wednesday 10 October 2018

Good enough

I'm an evolutionary biologist: I've spent a life-time tracking how living things are different and speculating how they got that way. Charles Darwin is credited with the idea of evolution by natural selection. The two most familiar phrases associated with the idea are "nature red in tooth and claw" and "survival of the fittest" neither of which were coined by Darwin! The first is from In Memoriam by Tennyson and the other was first used by Herbert Spencer in his Principles of Biology (1859). My beef is that you don't need to be the fittest to survive (and leave a parcel of offspring) you just need to be fitter than the chap next door. As the old saw has it, you don't need to out-run a hungry lion, you just need to out-run the other fellow on the road. So for me, evolution is the history of good enough. And that has sort of informed my life: I didn't need to be the smartest, fastest, honestest kid on the block.

On Friday afternoon, I was looking for one of the technicians which is quite aspirational because The Institute has many of the attributes of the Mary Celeste after lunch on Fridays. I noticed a lonely white-coated body in the lab and went over to commiserate about the loneliness of the long-distance scientist. Turned out he was an outside contractor at the end of his day 'calibrating the autoclaves'. I've written quite a bit about autoclaves on The Blob, partly because I am terrified of the things and partly because I want to make sure none of my students have a damaging hot, wet, pressurised accident while using one. Accordingly, I pointed to the beige splodge on the lab ceiling where a student had launched boiling agar skywards as well as catching some on her face. Then I told him about appointing students Autoclave Liaison Officer so they'd learn how to use that equipment safely. Having unloaded on the poor visitor, I then asked what he was doing and how he was doing it.

Seems he was popping a WiFi thermocouple into each instrument, firing it up and capturing to his laptop the actual temperature on the 40 minute heat - hold - cool cycle. tsk, tsk, he shared, that autoclave is not actually holding its temperature for the full 15 minutes. But he wasn't about to fix it, he was only the calibrator. The SOP standard operating procedure says to heat the thing up until it achieves a pressure of 15 p.s.i. and a temperature of 121oC. In any closed system these two statistics are locked together by Gay-Lussac's Law: P/T = constant. On our autoclaves, because the pressure P is measured on a gauge [L: Top L] we don't really need the temperature gauge [L: Mid R] because we believe St Joseph of Gay-Lussac. When the needle reaches the red zone on the dial, we say, then start timing 15 minutes. But one of our autoclaves never quite reaches the red zone because the gauge is set low, and a certain type of student sits around waiting for godot red while everyone else goes to get a cup of tea and a bun. Go on with you, I say, it's good enough at that temperature or if you want to compensate then leave the stuff in for 20 minutes instead of 15 . . . have two buns while you're about it.

Because 15 p.s.i. and 121oC are only rough rules-of-thumb that have worked in most cases, most of the time since 1884 and therefore they must have a good whack of tolerance built in. It's a racing certainty that your Petri dishes won't be contaminated if only 118oC is achieved. You sort of know this is a makey-uppy seat-of-pants measure because 15 p.s.i. is as near as dammit 1 atmosphere (or 100 kiloPascals in new money).  The value, originally chosen for convenience, has now become an article of faith. Part of the training that scientists should get is that they learn when to cut corners safely rather than slavishly following holy writ the SOP.

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