Halons are bromochlorofluorocarbons which have been used extensively
for fire extinguishing. They are amongst the worst substances known for
depletion of the ozone layer. These
substances are very effective and it is difficult to find substitutes
that are satisfactory for all applications.
For example, computer rooms have to have an extinguishing agent that will
not cause damage to the contents, including data storage devices. Obviously,
water cannot be used for electrical fires and powder extinguishers would
cause malfunctioning. Carbon dioxide gas flooding would be a possibility,
except that anyone in the room when the gas was released would be
suffocated!
The real problem though is with aircraft and ships. Halons are critical
for their safety. However, it was found that most of the use of halons was
not for fire-fighting but for testing fire-fighting systems. As these have
already been deemed very reliable, rules were brought in to forbid releasing
halons during testing. Many countries set up halon banks with unused and
recycled products for replenishment of supplies for critical aircraft and
ship use. Current halon manufacture is negligible.