Resources - Safety Info

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From November 1992 edition of ‘Crucible’ Volume 23.5

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The current controversy concerning the classroom use of mercury thermometers and the necessity to substitute them for a safer alternative has left most of us with a stock of ‘stored’ mercury thermometers and budgets severely stressed in an attempt to purchase some viable replacements.

We all know that cleanup after a mercury thermometer can be hazardous (the TLV* for mercury is reached if four mercury thermometers are broken in a room 12.2 m x 9 .1 m x 2.7 m). It is also a procedure which can be very costly. It is for these two reasons that many believe an alternative to the mercury thermometer should be found.

An obvious replacement for the standard mercury thermometer is the alcohol thermometer. One of the arguments against alcohol thermometers however is their relative inaccuracy. According to a researcher for the University of Wisconsin’s Environmental Notes, alcohol thermometers "have a lower usable range than do mercury thermometers, typically being accurate only below 300C". The range for the alcohol thermometers in most catalogues is -20 to 200C. A second problem is the separation of the alcohol column; however, most catalogues and retailers provide hints on how to overcome this problem with both alcohol and mercury columns. A third consideration is cost. The price of an alcohol thermometer depends on quality, quantity and immersion depth. However, in most cases, their prices are comparable to mercury thermometers.

The Teflon coating now available for both the mercury and alcohol thermometers may help to solve the problems of durability and spill cleanup. The special coating is intended to make the thermometers shatterproof and resistant to acids and corrosive chemicals.

Digital thermometers are available ranging from -250 to 1 375C for approximately $400, and ranging from -50 to 170C for about $50 with resolution and precision varying according to price.

Consideration given to factors of cost, safety and efficiency, the choice is up to you, the Science teacher. Do we use mercury thermometers and shut down the lab when one is broken? Do we use Teflon coated mercury thermometers and hope the coating contains the spill if the thermometer is broken? Do we use alcohol thermometers and sacrifice accuracy above 300C, and clean up the mess of an accident ourselves? Or do we spend a fortune and get one expensive digital thermometer to be used in five labs by 200 students and five irate teachers all at once?

Given the alternatives, the STAO Safety Committee recommends that alcohol thermometers be used by students up to and including grade 10. In senior Science courses, teachers should give serious consideration to the use of mercury thermometers with Teflon coating. If mercury thermometers are to be used, a mercury spill procedure must be in place.

* TLV = Threshold Limit Value