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There was an incident a couple of years ago where a teenage girl during an art lessen got her hands stuck in a bucket with plaster. As the plaster set, the heat from the chemical process caused her fingers to melt (it says in the article that the temperature reached 60 °C; I am not sure how this can melt your fingers, but this seems to be the case). As a result, she had to have all but two fingers amputated. The lesson we seem to learn is that sticking your hands into a bucket with plaster is a bad idea.

At the same time, plaster casting the human body is something that people do all the time, both in art and for medical purposes. Of course, the layers are thinner in this case. So, what are these people doing differently than in that school incident? Could they be using a different kind of plaster that generates less heat?

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    $\begingroup$ Your cast has a far larger relative surface than that bucket. Also the incident was in Boston, if you read that link carefully. Plaster of Paris, not in. $\endgroup$
    – Karl
    Oct 11 '19 at 0:17
  • $\begingroup$ Also you can mix the plaster with a large amount of inert filler if you absolutely want to put your hand in a full bucket, instead of just wrapping it in bandage with some plaster added. And think about how to get your hand out again without heavy machinery. Seems the stuff only becomes hot after it has already set ... $\endgroup$
    – Karl
    Oct 11 '19 at 0:32
  • $\begingroup$ I once fixed a boat hull outside with some two component epoxy. It was under direct sunlight and I did the error of wanting to do some final smoothing of an uneven blob with a hand. That glue was smoking hot. Using it under direct sunlight was probably an oversight. UV light accelerates many things epoxy-like. Getting my hand out of the rapidly heat-shrinking/deteriorating glove was fortunate. $\endgroup$ Nov 11 '19 at 7:56
  • $\begingroup$ The thermal effect depends strongly on the amount of plaster and the surface area of the object filled with plaster. A bucket filled with plaster will reach a much higher temperature than a thin layer of plaster (as used in fixing broken bones). $\endgroup$
    – matt_black
    Jul 7 '20 at 11:01
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What are these people doing differently than in that school incident?

The plaster casting of the human body is a totally different process compared to the incident at school. At school, it was a liquid plaster of Paris paste ready for molding. Nowadays, plaster casting is done in medical purposes differently.

  1. First they put thin stockinette (e.g., Delta Net®) covering the injured joint or around it covering all of the area that needs to be cast.
  2. Then, put padding (e.g., Soffban®) over the stockinette. Wrap padding at least twice over the area.
  3. Then apply wetted plaster of Paris bandage (Trade names: Gypsona®, Specialist®, Platrix®, or Biplatrix®) over the padding.
  4. To secure the Plaster of Paris bandage, wrap around elastic or cohesive bandage (e.g., Elastomull® or Tensoplus®) over.

As you see, no liquid plaster of Paris paste has been used. The process just uses wetted plaster of Paris bandages, the extra water of which is also removed before wrapping around the injured surface. The videos of this, this, and this would help you understand the process clearly.

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The thermal effect depends on the amount of water used. If you mix plaster of Paris with 0.6 times its amount of water (in weight) at $20$°c, the temperature will not go higher than $37$°C.

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  • $\begingroup$ You can't make such a strong blanket statement. For instance, it doesn't account for the temperature of the water being used. $\endgroup$
    – theorist
    Jul 5 at 0:47

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