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2) Health, Safety and Accident Prevention - Oxyacetylene Welding, Cutting and Heating (1)

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  Health, safety and accident prevention - oxyacetylene welding, cutting and heating  Guidelines are given on the principal health and safety considerations for oxyacetylene welding to ensure safe welding practices. Health, safety and accident prevention Oxyacetylene welding, cuttingand heating Guidelines are given on the principal health and safety considerations foroxyacetylene welding to ensure safe welding practices. The oxyacetylene process The oxyacetylene process produces a high temperature flame, over 3000 degrees C,by the combustion of pure oxygen and acetylene. It is the only gas mixture hotenough to melt steel other gases !propane, #G or hydrogen$ can be used for lowermelting point non%ferrous metals, for bra&ing and silver soldering and as apreheating'piercing gas for cutting. Safe storage Gases are normally supplied under high pressure in steelcylinders in the (), the colour coding for the cylinders is inthe process of being harmonised across *urope. +oracetylene the shoulder of the cylinder is maroon and foroxygen the shoulder is white, although blac oxygencylinders will remain in circulation for some time. Thecylinder should also have a label mared with the type of gas. To prevent the interchange of fittings between cylinderscontaining combustible and non%combustible gases, oxygencylinders have a right%hand and acetylene have a left%handthread. -ll cylinders are opened by turning the ey or nobanticlocwise and closed by turning them clocwise.xygen will cause a fire to burn more fiercely and a mixture of oxygen and a fuel gascan cause an explosion. It is, therefore, essential that the oxygen cylinders areseparated from the fuel gas cylinders and stored in an area free from combustiblematerial. Safe practice and accident avoidance  ã /tore the cylinders in a well%ventilated area, preferably in the open air ã The storage area should be well away from sources of heat, spars and fireris ã Cylinders should be stored upright and well secured ã xygen cylinders should be stored at least 3m from fuel gas cylinders orseparated by a 30 minute fire resisting barrier ã The store area should be designated 1o /moing. Handling compressed gases Cylinders are fitted with regulators to reduce the gas pressure in the cylinder to theworing pressure of the torch. The regulator has two gauges, a high pressure gaugefor the gas in the cylinder and a low pressure gauge for the gas being fed to thetorch. The gas flow rate is controlled by a pressure ad2usting screw which sets theoutlet gas pressure. The CG- Code of #ractice C#4 recommends the gauges arecheced annually and replaced every 5 years.+actors to be considered are that the gas system is suitable for the pressure ratingand the hoses are connected without any leas. 6alve threads should be cleanedbefore screwing in the regulator. The valve of an acetylene cylinders can be openedslightly to blow out the threads but the threads in oxygen cylinders are best cleanedusing clean compressed air !the threads on hydrogen cylinders must always be blownout using compressed air$.-s oxygen can react violently with oils and grease, lubricating oils or sealant for thethreads must not be used. Safe practice and accident avoidance ã Cylinders are very heavy and must be securely fastened at all times ã Cylinder valves or valve guards should never be loosened ã Chec the regulator is rated for the pressure in the cylinder ã 7hen attaching the regulator to the cylinder the 2oints must be clean andsealant must not be used ã efore attaching a regulator, the pressure ad2ustment screw must be screwedout to prevent unregulated flow of gas into the system when the cylindervalve is opened Using compressed gases Gases are mixed in the hand%held torch or blowpipe in the correct proportions. 8osesbetween regulator and torch should be colour coded in the (), red for acetylene andblue for oxygen. 8oses should be ept as short as possible and users should checperiodically that they are not near hot or sharp ob2ects which could damage the hosewall. -cetylene cylinders must always be used upright.7hen connecting the system, and at least at the start of each shift, hoses and torchmust be purged to remove any inflammable gas mixtures. It is essential the oxygenstream does not come into contact with oil which can ignite spontaneously. #urgingshould also not be carried out in confined spaces.  The torch should be lit with a friction lighter or stationary pilot flame to avoid burningthe hands matches should not be used and the flame should not be reignited fromhot metal, especially when woring in a confined space.The cylinders should not become heated, for example by allowing the torch flame toheat locally the cylinder wall. /imilarly, arc welding too close to the cylinder couldresult in an arc forming between the cylinder and worpiece'electrode.-lthough very little (6 is emitted, the welder must wear tinted goggles. The grade of filter is determined by the intensity of the flame which depends on the thicness of metal being welded recommendations for filters according to the acetylene flow rateare given in the table !/*1 9:;<9;;=$.Grade of filter recommended according to the acetylene flow rate< Workflow rate of acetylene in l/hr up to7070 -200200 -800over 800Welding and braze welding of heavy metals e.g. steels, copper and their alloys! 7Welding with emittive flu#es $notably light alloys%a!a a7a Safe practice and accident avoidance ã 7hen cleaning the cylinder threads, connecting the regulator and purging thehoses, protect face and eyes by wearing the appropriate head shield ã (se a suitable welding shield e>uipped with the appropriate ocular protectionfilter ã 7ear non%combustible clothing ã *nsure the cylinder is not heated by the flame or by stray arcs from ad2acentelectrical e>uipment Leak detection ?oints and hoses should be checed for leas before any welding is attempted. 7hilstacetylene may be detected by its distinctive smell !usually at levels of less than =@$oxygen is odourless. ea detection is best carried out applying a wea !typically 0.5@$ solution of adetergent in water or a lea detecting solution from one of the gas supplycompanies. It is applied to the 2oints using a brush and the escaping gas will formbubbles. n curing the lea, the area should be cleaned to remove the residue fromthe lea detecting solution. eas in hoses may be repaired but approvedreplacement hose and couplings must be used in accordance with /*1 5:0<9;;5and /*1 9=5:<9;;:. ackfire and flash!ack  - bacfire !a single cracing or popping sound$ is when the flame has ignited thegases inside the no&&le and extinguished itself. This may happen when the torch isheld too near the worpiece.- flashbac !a shrill hissing sound$ when the flame is burning inside the torch, ismore severe. The flame may pass bac through the torch mixing chamber to thehose. The most liely cause is incorrect gas pressures giving too low a gas velocity.-lternatively, a situation may be created by a higher pressure gas !acetylene$feeding up a lower pressure gas !oxygen$ stream. This could occur if the oxygencylinder is almost empty but other potential causes would be hose leas, looseconnections, or failure to ade>uately purge the hoses.1on%return valves fitted to the hoses will detect and stop reverse gas flow preventingan inflammable oxygen and acetylene mixture from forming in the hose. Theflashbac arrestor is an automatic flame trap device designed not only to >uench theflame but also to prevent the flame from reaching the regulator. ackfire or flash!ack procedure -fter an unsustained bacfire in which the flame is extinguished< ã close the blowpipe control valves !fuel gas first$ ã chec the no&&le is tight ã chec the pressures on regulators ã re%light the torch using the recommended procedure If the flame continues to burn< ã close the oxygen valve at the torch !to prevent internal burning$ ã close the acetylene valve at the torch ã close cylinder valves or gas supply point isolation valves for both oxygen andacetylene ã close outlets of ad2ustable pressure regulators by winding out the pressure%ad2usting screws ã open both torch valves to vent the pressure in the e>uipment ã close torch valves ã chec no&&le tightness and pressures on regulators ã re%light the torch using the recommended procedure If a flashbac occurs in the hose and e>uipment, or fire in the hose, regulatorconnections or gas supply outlet points< ã isolate oxygen and fuel gas supplies at the cylinder valves or gas supplyoutlet points !only if this can be done safely$ ã if no ris of personal in2ury, control fire using first aid fire%fighting e>uipment ã if the fire cannot be put out at once, call emergency fire services ã after the e>uipment has cooled, examine the e>uipment and replace defectivecomponents 7hen a bacfire has been investigated and the fault rectified, the torch may be re%lit.-fter a flashbac, because the flame has extended to the regulator it is essential notonly to examine the torch, but the hoses and components must be checed and, if 
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