A range of new chemicals, used in everything from fire extinguishers to cleaning fluids, are appearing on the market to the concern of scientists studying the ozone layer. The new substances, with names such as n-propyl bromide and halon-1202, are not controlled by the Montreal Protocol, the 1987 international treaty that lists ozone-depleting substances that are to be phased out. Studies indicate that some of the new substances, which are being used as replacements for banned ones, may have the potential to damage the ozone layer.