Your thoughts on exploding tanks, dicholoromethane and closing down the lab for Christmas
Santa’s little helpers
It was the night before Christmas and all through the lab not a creature was stirring… apart from the safety team doing the shutdown. Spare a thought this festive season when you are happily down the pub for those left behind ensuring the building is still intact for your return. The last few users are ushered out and the doors closed yielding only to those who have drawn the short straw in keeping the cryogens topped up and cultures alive.
In theory, this is a simple task of checking everything is switched off, doors locked and regents put away. In reality, it becomes a marathon of problem solving as ladders are sought so that malfunctioning fume cupboards can be isolated, leaking windows are plugged with whatever we can find (normally lab coats) and wet floor signs are dug out because there is no one sober left in campus services and there is water running down the wall.
It is also a once-a-year opportunity for a quick lab and office inspection while the users are way, so you had better be sure you have not been naughty! Indeed, the Santa comparison does not end there: many abandoned mince pies are consumed in the name of clearing up!
Charles Harrison MRSC
University of Exeter, UK
Tank trouble
I have a question about the action required for a bulging tank of sodium hypochlorite solution in September’s On the spot (Chemistry World, September 2017, p73). The answer given suggests that chlorine could be the cause of the bulging tank and precautions should be taken for a toxic gas. Sodium hypochlorite solution is supplied with an excess of alkalinity and under alkaline conditions it decomposes slowly to sodium chlorate or oxygen. The decomposition to oxygen can be increased by heat or catalysis by some transition metal ions. It seems more likely in this case that the pressurisation in the tank is due to oxygen gas, and the gas can be released by opening the cap.
A M Couper CChem MRSC
Northwich, UK
Tom Baker, senior responder at the National Chemical Emergency Centre, replies:
You’re quite right: sodium hypochlorite solutions can evolve oxygen as they decompose, which we didn’t acknowledge in our solution. However, a large proportion of the incidents we respond to are the result of accidental contamination. We tend to default to the worst case scenario – in this case acid contamination – as in an incident as we will have limited information. We do this to allow the Fire Service to take appropriate measures to ensure they’re protected in case the worst happens.
Dichloromethane facts
Thanks to Mark Peplow for bringing the subject of dichloromethane and its alleged action as an ozone-depleting chemical to a wider readership (Chemistry World, August 2017, p15), based on the findings and predictions of a recent paper by Hossaini et al.1 However, Peplow’s comment that ‘acknowledging that the problem exists would be a good first step’ is, I suggest, unfair. As a producer of dichloromethane, it appears that we can be criticised for rushing out reactive statements on papers which identify problems. Here, we are criticised for conducting detailed evaluation before responding to new findings.
Thanks to Mark Peplow for bringing the subject of dichloromethane and its alleged action as an ozone-depleting chemical to a wider readership (Chemistry World, August 2017, p15), based on the findings and predictions of a recent paper by Hossaini et al. However, Peplow’s comment that ‘acknowledging that the problem exists would be a good first step’ is, I suggest, unfair. As a producer of dichloromethane, it appears that we can be criticised for rushing out reactive statements on papers which identify problems. Here, we are criticised for conducting detailed evaluation before responding to new findings.
The development of meaningful reactions to external publications based on scientific rigour for such complex issues does, unfortunately, take some time. It will come, and there has already been a formal expert reaction prepared. While we will always respect academic freedom, it’s important to discuss things together and base regulations on sound, repeatable science that involves accurate market statistics.
Unfortunately, the Hossaini paper has several errors. For example, in the paper there is a correlation between use of dichloromethane and levels in the atmosphere but the paper also makes false assumptions about unrealistically high growth rates of dichloromethane production, while in reality production capacity has been stable for a number of years. A key aspect here is that the use is a feedstock use: the dichloromethane is consumed. There are feedstock exemptions under regulation 1005/2009 – and numerous specified containment obligations in other regulations – so it does not follow that increasing use of dichloromethane in this application results in higher atmospheric levels. The authors also mention that dichloromethane is used extensively in manufacture of HCFC22. It is not. It is chloroform, the manufacture of which also produces dichloromethane, which is used in the manufacture of HCFC22.
A reality check by the authors would have helped, and we would have willingly entered into discussions. We would also be delighted to make the formal expert reaction to the paper available to anyone interested.
Chris Howick CCsi CChem FRSC
Inovyn Chlorvinyls
Runcorn, UK
Reference
R Hossaini et al, Nat. Commun., 2017 DOI: 10.1038/ncomms15962
Steamy recollection
I have a distinct memory of reading a piece in New Scientist in the mid-1960s which described a process for recycling polyethylene essentially by steam distillation. As I recall, steam at 130–140°C was passed over the waste polyethylene which caused it to volatilise, leaving behind colorants and other impurities. The polymer was then condensed and could be reused.
Does anybody know what happened to this process? Was it ever commercialised, or am I making it up?
Barry Knight MRSC
St Albans, UK
References
R Hossaini et al, Nat. Commun., 2017 DOI: 10.1038/ncomms15962
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