Methyl Isocyanate In Student Laboratories
To the Editor: I received the August 1984 edition of this Journal shortly after reading about the tragedy in India where more than 2000 people were killed and many others were left with permanent disabilities because of an accidental escape of methyl isocyanate (CH3-N=C=O) into the atmosphere. In that issue I came upon a laboratory experiment titled, "Synthesis and Testing of the Insecticide Carbaryl" ( I ). The synthesis given uses methyl isocyanate as one of the reagents. I was astonished to note that the authors make no mention of its toxicity. They do, however, indicate that this substance is anowerful lachrvmator and. for this reason, the and diipensed t o the stusolution used should be dents in a hood. Subsequently, the instructions indicate that the reaction vessel, a 25-mL flask or a 6-in. test tube, should he fitted on a steam bath a t the students' desks. For methyl isocyanate, the threshold value limit (TLV, American Conference of Governmental Industrial Hygienists-1967) is 0.02 ppm (0.05 mg/m3) (2,3). Considering the quantities given in the experiment, and assuming a laboratory of 270 m3 (6 m X 15 m X 3 m), it can be calculated that a spill during the preparation of the solution would provide the equivalent of 201.4 mg/m3 (4028 times the TLV). If there is any leakage from the hood, the TLV value could he exceeded easilv. However. s u n ~ o s i n ethat this does not hapof; solution containing 0.87 pen, each &dent receives e of methvl isocvanate. If one student drops his flask, the level of mkthyl
