Search result for: FLAMMABLE GASES, VAPOURS & LIQUIDS

Hydrogen is a special case: it forms violently explosive mixtures with air in almost any proportions and spontaneously combusts at concentrations greater than 4% in air.
Use this gas for demonstration purposes only in extremely small quantities. Safe methods have been developed using soap-bubble techniques.

The mishandling of flammable solvents has probably caused more fires and personal injuries in chemical laboratories than anything else.

A common injury relates to the burning of loose long hair.
Staff and students must have securely fixed and contained hair to reduce the risk of burning or contact with laboratory apparatus. This can be achieved by the tying back of the hair or by use of caps or hairnets.

Diethyl ether, for example, evaporates readily (boiling point 35C), forming a heavy vapour in air, which can travel several metres along the bench or floor in a gentle air current.

Carbon disulfide has a greater flammability than ether. It forms even more dense vapours, and the vapour has an amazingly low ignition temperature (<100C). Even a water bath can ignite it.
Both ether and carbon disulfide are banned from use in schools. Methylated spirits (or ethanol) and hydrocarbon solvents (petroleum spirit, hexane, etc.) pose the greatest risk in schools.

Mixtures of air with any of these materials are highly flammable, and ignition of vapour is usually followed by a fire in or around the solvent container. Flammable solvents become more difficult to ignite as their boiling points rise, so use the highest boiling-point solvent possible.

Solvent alternatives are suggested for individual chemicals elsewhere in Appendix D. Water baths should be used to heat volatile flammable solvents.

Note: Flammable solvents should not be used directly by students Years K-6. Solvents should only be used by staff with students after assessment of the risks, which include not only flammability but their toxicity including possible allergic reactions.