Self heating cans were used a lot by the military and explorers, and
there is a nice article here about people's experiences using them, as
they did not always work as planned:
http://www.thejournal.ie/self-heating-soup-cans-1370166-Mar2014/
In the Polar Museum collection in Cambridge there are Heinz cans which
used a self-heating mechanism patented by ICI in 1942. This was only
one of several patents relating to self-heating food packages, and it
seems there were different mechanisms and different heating chemicals
used at various times. The oldest form of self-heating can used pockets
of quicklime, which was exposed to water when the tin was punctured in a
certain place. The Heinz ICI cans were different and used a
nitrocellulose fuse and a mixture of red lead and calcium silicide and
talc which react to give off heat. The whole patent description for
this mechanism is here:
https://www.google.com/patents/US2384278
The hazards from these tins will vary according to which mechanism they
have, so if it is possible to see the patent number and look it up on
the Google patents site this should help work out what the issues might
be. The ICI/Heinz tins from the 1940's contain a poison (red lead) and
calcium silicide which can spontaneously combust in air. The
nitrocellulose fuse might also be a risk. For tins which use quicklime
there is a risk if the contents are exposed to water and also a risk of
burns to the skin in handling, if the quicklime gets out of the tin.
It would be worth considering using an oxygen free enclosure (e.g.
vapour barrier film with Ageless) for tins which are corroding and might
contain calcium silicide - this would keep air away from the chemical,
slow down the corrosion if the RH is kept low and would also help
protect anyone handling the tins. If the tins are so corroded that the
contents are coming out then you could consider disposing of the whole
thing or, preferably, the hazardous components only. Obviously this
should only be done ethically after full consultation and the waste
should be disposed of legally and responsibly.
--
Sophie Rowe ACR
Conservator
Scott Polar Research Institute
Lensfield Road
Cambridge CB2 1ER
Tel: 01223 761813
http://www.spri.cam.ac.uk/museum/
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