Sentences with word «halon»

By international agreement, however, production of all types of halons ceased in 1994 because the bromine and chlorine atoms in the chemical were found to migrate over time to the stratosphere, where they react to deplete ozone in a very efficient catalytic cycle.

Indeed, bromine and chlorine atoms are released as halons decompose in the heat of the fire, establishing a catalytic cycle involving HBr and HCl; the cycle converts active hydrogen atoms to stable H2 molecules, breaking the chain reaction.

Beginning in 1987, the internationally agreed - upon Montreal Protocol on Substances that Deplete the Ozone Layer has regulated these ozone - depleting compounds, such as chlorine - containing chlorofluorocarbons used in refrigerants and bromine - containing halon gases used as fire suppressants.

These properties made halons an ideal choice for protecting computers, archives and works of art.

There is no easy substitute for halons in fire fighting, a seminar organised by the Civil Aviation Authority was told last week.

Its Technology and Economic Assessment Panel, which will be the final arbiter, has already refused to allow any exceptions to the ban on halons despite pleas to be allowed to use them in certain types of fire extinguishers used on planes and trains.

Nine - tenths of the world's current halon production is in China.

Some industrialised countries have built up large stockpiles of recycled halons, as none has manufactured the chemicals since 1994.

The company has trained workers to use water to fight electrical switchgear fires if halon is not available, the report said, raising the risk of flooding in adjacent rooms with electrical controls because flood doors have not been established.

In addition to allowing firefighters to control fires from a safe distance, the FIT - 5 could also replace halon fluorocarbons, an effective fire - fighting tool until they were banned in 1994 after it was discovered that they destroy Earth's ozone layer.

Because halon displaces oxygen, it extinguished electrical, grease and other fires that water alone could not, says Robert Kaul, ARA Safety's technical director.

The need to find halon replacements remains.

Concentrations of ozone - depleting halons in the lower atmosphere are levelling off, according to research carried out by US scientists working for the National Oceanic and Atmospheric Administration at Boulder, Colorado.

The Dutch government has helped set up a national halons «bank» to ensure the most effective use of the chemicals; Britain is considering following suit, Ann Godfrey, a senior official at the Department of the Environment confirmed last week.

Firefighters have called on the world's users of halons not to destroy the ozone - depleting chemicals — or worse, release them into the air — as old fire - extinguishing systems are junked.

NASA is conserving stocks by cutting unnecessary emissions, according to Michelle Collins, who manages the space agency's halon bank.

«The world's entire commercial aircraft fleet is protected by halon - 1301,» says Taylor.

But he urges continued monitoring of other harmful and long - lived compounds still in use, including halons with bromine that are present in fire extinguishers.

Set up in 1987 this agreement has seen levels of ozone - depleting gases such as chlorofluorcarbons and halons above the Arctic fall by 10 % of the amount that would bring them back to the 1980 benchmark level.

NASA's space shuttle fleet and its launch facilities are protected by 40 000 pieces of firefighting equipment containing halon - 1301.

David Ball, the company's development director, admits that the new products are not direct substitutes for halons.

But last month, the European Commission announced that it will allow companies to import 2000 tonnes of halons, with an ozone - destroying potential equal to 20 000 tonnes of CFCs.

A ban on halons, used in fire extinguishers, will be brought forward from 2000 to 1994.

Methyl bromide, used in agriculture, and halons, which are used to fight fires, are the principal humanmade sources of the chemical, and their use helped double the amount of bromine in the atmosphere from the mid to the late 20th century.

The company had not assessed the capability of a halon fire suppression system that protects essential switchgear rooms.

The Montreal Protocol and associated agreements have led to decreases in the atmospheric abundance of gases, such as CFCs (chlorofluorocarbons) and halons, once used in products such as refrigerators, spray cans, insulation foam and fire suppression.

Halons, used as fire extinguishers, have been banned since 1 January.

These companies have invested heavily in alternatives to CFCs and halons, and say sales of their replacements are being limited by a black market in the old ones.

None have been identified with all the positive qualities of halon 1211 and halon 1301.

The phaseout of halons has led to a scramble by government and industry researchers to find environmentally suitable replacements.

Bromotrifluoromethane (CF3Br, or halon 1301) is a close cousin to halon 1211, but has a much lower boiling point and toxic level — properties that have made halon 1301 the firefighting chemical of choice for applications where sprinklers can not be used.

The trick is that the bromine and chlorine atoms in the halon molecule — the very ones that are so damaging to the stratospheric ozone — are also incredibly aggressive scavengers of hydrogen atoms, which are key to maintaining a combustion chain reaction.

The most effective and common fluorocarbon used until recently for this application had been bromochlorodifluoromethane (CF2ClBr), referred to as halon 1211.

Manufacturers have introduced new families of chemicals containing no chlorine or bromine, called hydrofluorocarbons (HFCs), that have physical properties similar to the halons and no ozone depletion potential.

The Montreal Protocol agreement beginning in 1987 regulated ozone depleting substances, such as chlorine - containing chlorofluorocarbons and bromine - containing halons.

These include methane, nitrous oxide («laughing gas»), halons, methyl bromide and chlorofluorocarbons (CFCs), which are notorious as «ozone killers» because they play a major role in ozone depletion in the polar regions.

The countries that have signed the Montreal Protocol have agreed to ban some of the most destructive chemicals, including CFCs and halons, much earlier than originally planned.

However, the company's technical service manager Jan Haeck, told the seminar that none of the agents under trial could match the performance of halons.

Halons are known as «super gas» in the fire protection industry because they are non-conducting, have low toxicity and put out fires fast.

ICI has been trying to develop substitutes for halons 1211 and 1301.

As the deadlines for ending the manufacture of halons and CFCs nears, users are being forced to introduce alternatives or depend on recycled stocks from hastily set up «banks».

France, Britain and Belgium all argued that they should be allowed to continue to make some halons, claiming they are needed for the new generation of trains designed to run through the Channel Tunnel.

He believes that dry powder and water - based agents could be utilised more extensively as alternatives to halons.

The impending end of halon production is forcing the fire protection industry to consider recycling the halons already in use.

Gary Taylor, Canadian fire consultant and co-chair of the Protocol's Halon Technical Options Committee, says there are problems with supplies of halon - 1301, one of the two most widely used forms.

In confined spaces where firefighting chemicals have to be swift - acting but non-toxic, halon - 1301 will continue to be needed for a long time.

The concern is that these halons will eventually be released into the air rather than being recycled.

«It would be a tragedy for the world to gather up and destroy all the halons and then have to come back a couple of years later and restart production to supply airlines and the military,» says Taylor.