Imagine my surprise recently when I was pontificating about careers in chemistry, only to be interrupted by a student putting her hand into her pocket and exclaiming, “Ow, hot!” She held the pocket material away from her skin. I asked her what she had in there and she told me that she had a couple of batteries. I told her to take them out of her pocket, to which she replied that they were too hot to touch.
I initially thought she was burning from the battery acid coming into contact with her skin. In fact, when I retrieved a pair of crucible tongs for her to take out the hot batteries, she emptied the contents of her pocket and found that she had two 9 volt batteries (one hot, one cold) and a variety of coins. She had managed to create a short circuit with one of the batteries and the coins! In the end she came out of the incident with only a minor red patch on her skin. I was having a “Learning by Accident” moment even though I was not doing a lab or demonstration!
Comments from the Safety Committee
This incident shows that improperly handled or stored dry cells can cause injury if they are allowed to short circuit. The major danger is from heat and possibly fire if the batteries come in contact with combustible material. It has also been reported that two 9 V batteries were maliciously attached together (positive to negative) and hidden in a drawer of paper towels after an electricity lab activity in a secondary school.
Luckily the teacher had good classroom management practices and went in search of the two missing batteries. Ideally the class would not have been dismissed until a full accounting of all the supplies had taken place, but this is not always possible. Batteries left inside an electrical device can leak damaging the battery holder and the electrical contacts. It is best to remove batteries if the device is not used regularly (summer holidays).
More detailed advice with respect to the storage and safe use of dry cell batteries can be found in the STAO publication Safe on Science available for purchase from the STAO Science Store.
About Learning by Accident
Learning by Accident is an ongoing STAOBlog feature, in which real-life lab accidents or incidents are recounted and explained. The goal is to highlight the consequence of ignoring safety rules so that science educators will be further encouraged to become knowledgeable, and to take appropriate action, in areas of safety that affect their daily activities in the science classroom. Submissions are encouraged. Anonymity will be guaranteed. Please send written descriptions to email@example.com, and mark Attention STAO Safety Committee