To prevent leakage, odors, or reaction with air, tightly seal all containers of highly toxic, highly volatile, malodorous, carcinogenic or reactive chemicals. Make sure that caps and other closures are tight on all hazardous chemicals. A limited exception is freshly-generated mixtures such as acids and organics that may generate gas pressure sufficient to burst a tightly sealed bottle. Use commercially available vent caps or keep the lids loose until sufficient time passes to complete the reactions, and then tightly close the lids. Until all reactions are completed, the contents of the bottle are not waste, but are instead the last step of the chemical procedure.

The best seal is the screw cap with a conical polyethylene or Teflon insert (Figure 4.2). Seal the caps with tape or Parafilm® “M” as a further precaution. Additional protection can include wrapping the container in an absorbent paper, sealing it inside a plastic bag, and storing the bag inside a metal can with a friction fitting lid.

Figure 4.2
(Left) Screw caps with conical polyethylene inserts. (Right) Screw caps with Teflon inserts.