《WorkwithAcetylene乙炔英文安全.ppt》由会员分享，可在线阅读，更多相关《WorkwithAcetylene乙炔英文安全.ppt（12页珍藏版）》请在三一办公上搜索。
1、Work with Acetylene,Case study,Acetylene cylinder explosionAn operator was lighting an oxy/acetylene cutting torch.There was a flashback to the acetylene cylinder,which started to vibrate.Three minutes later the cylinder exploded.The cylinder split into two parts.The largest part shot through a wind
2、ow and travelled 23 metres before embedding itself in anembankment at the factory boundary.The workshop was badly damaged.The windows were blown out and the roof collapsed.The explosion also lifted the roof of the main factory building,which had to be replaced.The cost of the damage was over 1 milli
3、on.Fortunately,no-one was injured,because the operator realised that the cylinder was in a dangerous condition.He raised the alarm and the factory was immediately evacuated.,Case study,What went wrong?Acetylene is an extremely flammable gas.It is different from other flammable gases because it is al
4、so unstable.Under certain conditions,it can decompose explosively into its constituent elements,carbon and hydrogen.The operator did not fully appreciate the hazards of acetylene.He did not follow the recommended procedures or take adequate precautions.In particular:The correct lighting up procedure
5、 was not followed.The gas hoses were notpurged.The acetylene gas was not at the correct pressure.The gas cylinders were not protected with flashback arresters.A flashback can occurif there is a flammable mixture of fuel gas and oxygen in the hoses when the torch is lit.If it is not stopped,the flame
6、 will ignite the mixture and will travel backwards from the torch,along the hoses,through the regulator and into the cylinder.A flashback can trigger decomposition of the acetylene in the fuel hose,in the regulator and in the cylinder itself.,Hazards of acetylene cylinders,There are a number of inci
7、dents each year where a flashback into an acetylene cylinder triggers decomposition,leaving the cylinder in a dangerous,unstable condition.An explosion of the cylinder only three minutes after a flashback is extremely rare.In most cases,if the decomposition is identified at an early stage,there is t
8、ime for the building to be evacuated,the fire brigade to be called and for emergency action to be taken.To make an unstable cylinder safe,the fire brigade may have to apply cooling water for many hours.It could be several days before the cylinder can be moved,because moving the cylinder could restar
9、t or accelerate the decomposition.These incidents put at risk anyone in the vicinity of the cylinder and anyone who tries to make the cylinder safe,such as the emergency services.,Acetylene cylinders can be used safely,An acetylene cylinder has a different design from most other gas cylinders.It con
10、sists of a steel shell containing a porous mass.The porous mass is a cellular structure which completely fills the cylinder.The acetylene gas in the cylinder is dissolved in acetone which is absorbed by the porous mass.Decomposition of the acetylene is usually triggered by heat.For example,if the cy
11、linder is:involved in a fire;scorched by flames from a blowtorch;or involved in a flashback.The porous mass is designed to slow down or stifle any decomposition of the gas.From the start of decomposition to the cylinder exploding should take several hours.This will usually(but not always)provide tim
12、e for emergency action.,Acetylene cylinders can be used safely,Decomposition can be triggered more easily and can proceed more rapidly if:the porous mass has been damaged by repeated flashbacks or by mishandling or dropping the cylinder;the cylinder valve is leaking gas(an open or leaking valve incr
13、eases the rate of decomposition within the cylinder);or the acetylene in the hoses is above the pressure recommended by the supplier.For most welding and cutting processes,the acetylene pressure should not exceed 0.62 bar(9psi).(See note under References.),What can you do to prevent flashback?,Train
14、ingDo not use oxy/acetylene equipment unless you have been trained.Use the correct lighting-up proceduresBefore lighting the blowpipe,purge the hoses by opening the gas supply to each hose for a few seconds.This will flush out any flammable mixtures of gases in the hose.Purge one hose at a time and
15、close the blowpipe valve after purging.Use a well-ventilated area.Use a spark ignitor to light the gas.Use the correct gas pressures and nozzle sizes for the job.,What can you do to prevent flashback?,Handle acetylene cylinders with careDo not drop or jar them.Do not roll them across the floor.Keep
16、them in an upright position.Fit flashback arrestersFit flashback arresters onto the pressure regulators on both the acetylene cylinder and the oxygen cylinder.For long lengths of hose,fit arresters on both the blowpipe and the regulator.Note:The fitting of flashback arresters is not a substitute for
17、 safe working practices,What can you do to prevent flashback?,Maintain non-return valvesFit non-return valves(often called check valves)on the torch,to prevent backfeeding of gas into the hoses.Inspect regularly and replace damaged non-return valves.Note:non-return valves will not stop a flashback o
18、nce it has occurred.Keep nozzles in good conditionPoorly maintained nozzles cause turbulent gas flow,which increases the risk of flashback.Inspect nozzles regularly.Make sure they are not blocked by dirt or spatter.Replace damaged nozzles.Do not hold the nozzle too close to the workpiece.The nozzle
19、can overheat and cause a flashback.,If a flashback does occur:,Immediately close the cylinder valves,both acetylene and oxygen,if it is safe to do so.The flame should go out when the fuel gas(acetylene)is shut off.If the flame cannot be put out at once,evacuate the area and call the emergency fire s
20、ervices and the gas supplier.Check any acetylene cylinder which has been involved in a flashback or which may have been affected by fire or flames.If it becomes warm or starts to vibrate,evacuate the building immediately and call the emergency fire services.Also call the gas supplier.Do not attempt
21、to move an unstable cylinder.Direct water spray at the cylinder body,if it is safe to do so.Before using again,check flashback arresters and other components which may have been damaged by the flashback.Replace if necessary.If in doubt,consult the supplier.,References,More detailed advice may be fou
22、nd in the following publications:The safe use of compressed gases in welding,flame cutting and allied processesHSG139 HSE Books 1997British Compressed Gases Association Code of Practice CP7 The safe use of oxyfuelgas equipment(Individual portable or mobile cylinder supply).Revision 2:1996BS EN 730 G
23、as welding equipment-Equipment used in gas welding,cutting andallied processes,safety devices for fuel gases and oxygen or compressed air.General specifications,requirements and test.Hot work on small tanks and drums INDG314 HSE Books 2000Safety in gas welding cutting and similar processes INDG297 H
24、SE Books 1999Take care with oxygen:Fire and explosion hazards in the use of oxygen HSE8(rev2)HSE Books 1999*Acetylene pressure must not exceed 0.62 bar(9psi)unless equipment has beendesigned to meet HSE Exemption Certificate No 2 of 1989 issued by theExplosives Inspectorate,St Annes House,Stanley Pr
25、ecinct,Bootle,Merseyside,L20 3RA Tel:0151 951 4025 and British Compressed Gases Association Code ofPractice CP6 The safe distribution of acetylene in the pressure range 0-1.5 bar(0-22 lbf/in2).Revision 1:1998While every effort has been made to ensure the accuracy of the references listed inthis publication,their future availability cannot be guaranteed.,
