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Anne Marie Helmenstine, Ph.D.

Plaster of Paris - Exothermic Reaction Can Cause Serious Burns

By October 5, 2012

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You may have read a while back about how a school in Lincolnshire (UK) was fined 20,000 for failing to report a tragic accident in which a girl essentially lost her hands after immersing them in plaster of Paris to make a mold for an art project. Plaster of Paris is used in a lot of art and science projects, often very casually, though it is a potentially hazardous chemical.

First off, plaster of Paris, which is calcium sulfate hemihydrate, may contain silica and asbestos as impurities. Both of these materials are capable of causing permanent lung damage and other ailments if inhaled. Second, and more significantly, plaster of Paris mixes with water in an exothermic reaction. In the Lincolnshire accident, the 16-year-old girl was seriously burned when she immersed her hands in a bucket of plaster of Paris mixture. She was unable to remove her hands from the setting plaster, which may have reached 60°C.

Now, I'm not saying you shouldn't play with plaster of Paris. It's great for making geodes and molds and for many other projects. It's safe for kids to use, but only if they are aware of and can follow the proper safety precautions for working with that chemical:

  • Wear a mask when working with dry plaster to prevent inhalation of the calcium sulfate or impurities which may be present in the powder.

  • Wear gloves when working with plaster of Paris and avoid situations where your skin might be in contact with the plaster.

  • Avoid washing plaster of Paris down the drain, since the plaster can set up in the plumbing.
When it's used properly, plaster of Paris is a useful chemical to have around. Just be careful.

Make a Crystal Geode | Make Colored Chalk

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August 13, 2010 at 11:34 pm
(1) brandon wade says:

i inaild a small bit when i was working on a project will it hurt me cause i am scared

August 14, 2010 at 9:16 am
(2) chemistry says:

Brandon, No, it’s nontoxic. It’s not great for your lungs, but you’ll be fine :)

October 20, 2012 at 1:34 am
(3) Mike F says:

I’m an orthopedic technician and have worked with a lot of plaster products over my 16 year career(most commonly J&J splinting). I seldom mask, am I at risk?

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