Posted By Jane Blunt Luan There are many types of halon. The word stands for halogenated hydrocarbon, and the halogens are fluorine, chlorine, bromine and iodine. The commonest halons are Halon 1301 and 1211 commonly used in fire extinguishers. In the name the first digit tells you how many carbon atoms, the second digit the number of fluorine atoms, the third digit the number of chlorine atoms, the fourth the bromine and the fifth digit the number of iodine atoms. Anything unaccounted for is hydrogen. So halon 104 is carbon tetrachloride - one carbon, 4 chlorine. They are being phased out because they react with ozone when the waft up into the upper atmosphere, and destroy it very efficiently. Jane

Posted By Luan Jane, Thanks for your information making my mind clear. Nigel, Thanks for your definations and some additional infromation. From the defination of incident and accident, it seems they are excluded each other. my unstanding before is that the scope of incident can cover the scope of accidnet, which is right please? could Nigel or anybody can help? Could any body help on other questions? they are suspended in my mind for a long period... Thanks

Posted By Jane Blunt Dear Luan I think you will never define incident or accident precisely to everyone's satisfaction, because both words are used in everyday language. Even if we do succeed in defining the words to our satisfaction, we still have to communicate with those who have not been on our training courses and have not gone through the process of thinking about what the words mean. The health and safety person likes to look for root causes. However, in everyday life people often use the word accident to imply that nothing could have prevented it. I believe that this is the reason that those studying H&S are confronted with a trainer who is trying to make us think about our definition. We should be aware of the fact that people describing an accident to us may already have decided that it was something that could not have been prevented, simply because their perception of accident has a degree of helplessness attached to it. I don't loose too much sleep in trying to teach my colleagues what I mean by the two words. Instead I tell them to report anything where some person or thing was damaged, and near misses - the ...... "Phew, thank goodness I wasn't in the way of that" moments. Jane

Posted By Luan Thanks for everyboday's help. Can anyone help on the 2nd question? I realized it is about understanding of safety, but I can not explain it logically ...

Posted By John Allen Luan, Quantitative Risk Assessment is a type of risk assessment used to predict the likelihood of an undesired event occurring using numerical techniques. It was pioneered in the nuclear industry because there was no historical evidence on which to base risk assessments. Today it is commonly used in the process industry to determine the level of risk in plant both on and offshore handling hazardous substances and Flammable gasses/liquids. A very simple example would be as follows for an offshore installation handling flammables: There is a likelihood that a leak of flammable material will occur. This will be dependent on known factors eg the number of flanges or valves in a system but it will also depend on some factors which have to be estimated eg the likelihood of corrosion or a release ocurring during mainteance intervention (sometimes this information may be available from historical tables maintained by companies like DNV) If a leak occurs it has to form a stoichiometric mixture and find an ignition source before an explosion occurs. Figures for the probability of this happening are available or can be estimated. Finally is anyone in the area when this happens? Occupancy figures can be determined by survey and applied to decide the final figure. Is every one in the vicinity killed if an explosion occurs or could they escape? This can be taken further eg is the explosion contained or does it escalate? If escalate, then is sufficient time available to allow people to escape by helicopters or lifeboats ie does the temporary refuge have sufficient endurance to allow this to happen? This process can be illustrated graphically in the form of a tree where each decision is shown as a branch leading ultimately to the least desired event ie one or more fatalities. The probability of the fatality occurring is expressed as "one in n years". Typically any risk of individual fatality greater than 1 in a 1000 years is considered unacceptable. This is not an exact science and a lot depends on the assumptions made. It is therefore difficult to compare the QRA of two installations because different assumptions may have been applied. The best you can do is demonstrate that your own process has been rigorous and comes out with an answer that is the right area, if not you have a lot of remedial work to do on your plant. Hope this helps.

Posted By Luan Some times we say fire wall has 60' or 30' fire proof ability, could anybody help on the standards for defining these numbers? Thank you!