SERIES & NO. SMI - 118

Transcription

1 1 of 13 SUBJECT: USE OF OXYGEN - FUEL GAS EQUIPMENT I. PURPOSE To describe the methods, equipment, fire, safety and health procedures to be used when performing oxygen- fuel gas cutting or welding. II. REFERENCE Plant Engineering & Environmental Planning Office Procedure No Federal and State Occupational Safety and Health Acts American Conference of Governmental Industrial Hygienists III. FUNCTIONS AFFECTED Manufacturing Engineering Facilities Engineering Production Engineering Security & Fire Prevention Services Employee Safety Industrial Hygiene IV. OPERATIONS AFFECTED Chrysler Corporation V. INFORMATION AND INSTRUCTIONS A. General Information 1. The gases used for cutting and welding are oxygen, methylacetylene propadiene (Mapp Gas), acetylene and hydrogen. Acetylene, Methylacetylene propadiene (Mapp Gas) and hydrogen are called fuel gases. Acetylene is extremely explosive with an explosion range of 2.7% to 89%. Mapp gas has a very low explosion range (3.4% to 10.8%).

2 2 of Sparks produced by oxy-fuel gas welding may fly thirty feet (30') or more, retaining their heat for several seconds after landing. Because of this and other dangers involved in gas cutting and welding extreme caution is necessary. The equipment shall be operated only by qualified and certified personnel. (See M.T.I. SMI-1 16.) B. Use of Equipment 1. Inspection of Equipment The operator shall inspect welding equipment daily before starting work. Leaks shall be detected by applying soapy water to all joints and connections. Faulty equipment shall be repaired only by authorized personnel or replaced immediately. Only authorized and approved welding equipment shall be used. a. Cylinders shall be inspected to insure that they are: 1) Clean and free from oil and grease. 2) Provided with a fixed hand wheel on the valve or a key on the valve stem. 3) Free of defects and leaks. if leaks are detected they shall immediately be moved to the outdoors, away from sources of ignition. The Security and Fire Prevention Services shall immediately be informed of the defective cylinder location. b. Torches shall be inspected to insure that they are: 1) Clean and free from oil and grease. 2) Not leaking or damaged. 3) Not plugged. c. Regulators shall be inspected to insure that they are: 1) Attached to the proper cylinder. 2) Clean and free from oil and grease. 3) Not leaking or damaged.

3 3 of 13 4) Not supplying a pressure greater than 15 lbs. per sq. inch with acetylene; pressures greater than 1 5 psi may be safely used with Mapp Gas. 5) Not creeping. Creeping occurs when the regulator allows the passage of gas at an increasing rate and is indicated on the low pressure (working) gauge. 6) Positioned on the gas cylinders so that the oxygen and fuel gas regulators point away from each other. d. Hoses shall be inspected to insure that they are: 2. Installation of Equipment 1) Clean and free from oil and grease. 2) Positioned to prevent kinks and tangles and to prevent damage by passing trucks, flying sparks, hot slag, hot metals, 3) Free from cuts, burns, worn spots, and other defects. Damaged hoses shall be replaced immediately. 4) Cleaned by applying air pressure to new hoses before installation. (CAUTION: Air used for cleaning new hoses before installation on torch shall be clean air, free of oil, grease, or flammable gas, mists, or vapors.) The equipment and the operator's hands and gloves shall be free from oil and grease when oxy-fuel gas welding components are being assembled. a. Regulators 1) Regulators shall be used only on the cylinders for which they are intended. Green regulators with right hand threads shall be used only on oxygen cylinders; red regulators with left hand threads shall be used only on fuel gas cylinders. 2) Fuel gas regulators shall be attached to the appropriate cylinder, tested and adjusted as follows:

4 4 of Operation of Equipment a. Igniting the Torch a) The regulator is attached to the hose. b) The cylinder valve is cleared by opening the valve momentarily. c) The regulator pressure adjustment screw is released (loose). Care shall be taken to be sure the cylinder valve is closed and the regulator and hose are cleared of gas. d) The regulator is attached to the proper cylinder. e) The torch valve is opened. f) The fuel gas cylinder valve is opened 1/4 TO 1/2 turn. The oxygen cylinder valve is opened all the way. g) The connections are tested with soapy water if leaks are suspected. h) The torch valve is closed. i) The regulator is adjusted by turning the pressure adjusting screw on the regulator until the pressure reaches about pounds per square inch as indicated on the low pressure (working) gauge. j) The regulator shall be examined for creeping (see IV.B.1c, above). If creeping occurs, the regulator is replaced immediately- k) The torch valve is opened. l) The regulator is again adjusted for the proper welding gas flow. Acetylene regulators are adjusted to a maximum pressure of 15 pounds per square inch. Oxygen and Mapp gas regulators are adjusted to the pressure required by the type of welding to be done. Torches shall be ignited:

5 5 of 13 1) Only when both hoses are under pressure. 2) With the oxygen supply turned off at the torch. The oxygen supply is adjusted after the fuel gas is ignited until the flame reaches the correct length. 3) By a friction lighter. Matches or hot surfaces are never used. b. Operating the Torch Improper use of the torch is indicated by: 1) Backfiring A momentary passage of the torch flame to the torch mixing chamber. After a snap or pop, the flame returns to normal. Backfires are caused by: a) Holding the tip of the torch too close to the work. b) Knocking or rubbing the torch tip when welding. c) Corrosion on the torch tip. d) Insufficient fuel gas pressure when lighting the torch. e) A kinked hose or heavy object on the hose. f) A loose torch tip or dirt on the seat of the torch. 2) Flashbacks The burning of gases within the torch mixing chamber, indicated by a whistle. Flashbacks are: a) Caused by an insufficient volume of gas flowing through the hoses. b) Corrected by: 1) Extinguishing the torch (see IV.B.3.c., below)

6 6 of 13 2) Allowing the tip to cool. C. Precautions 1. General 3) Blowing oxygen through the torch for a few seconds to clean out accumulated soot. 4) Adjusting the gas flow. 3) Pre-Ignition The spontaneous igniting of the gas at some point with in the torch or tip. Pre-ignition is caused by: a) Permitting the tip to become over heated. b) An insufficient volume of acetylene. c. Extinguishing the Torch To extinguish the torch, the following steps shall be taken, in sequence: 1) The oxygen valve on the torch is closed. 2) The fuel gas valve on the torch is closed. 3) The valves on both cylinders are closed. 4) The valves on the torch are opened, one at a time, bleeding the gas from the hose. The first valve is closed before the second one is opened. 5) The valves on the torch are closed. 6) The pressure adjusting screws on the regulators are released. d. Prior to removal of a regulator from a cylinder valve the cylinder valve must be closed and all gas released from the regulator. a. Regulators and torches shall not be modified or repaired by the operator.

7 7 of 13 b. Copper fittings shall not be used on Mapp or acetylene equipment. Copper may form an explosive compound when exposed to Mapp or acetylene gas. c. When burning or welding on, or using fluxes or filler metals that contain toxic or hazardous materials, the Industrial Hygiene Department shall be contacted for special instruction. d. Acetylene shall not be used at pressures above 15 pounds per square inch. e. Excessive oxygen pressure, while welding, shall be avoided. Greater pressures cause extra sparks and increase the flow of slag. f. Gas cylinders and hoses shall be kept away from the burning torch. g. The regulator shall not be opened to increase the gas pressure when the cylinder pressure is lower than desired. h. Hoses and torches shall not be hung from the cylinder valves or regulators. The weight of this equipment may damage the valves or regulators. i. Torches shall not be placed in small confined spaces. An accumulation of unburned gases in such a space may cause an explosion. j. Cylinder valves shall be closed except when actually using gas. Cylinder caps shall be installed at all times except when cylinder is connected for use. k. When working in confined spaces the instructions in M.T.I. SMI- I 1 0 "Safety and Health Requirements for Working in Confined Spaces" shall be followed. Cylinders shall not be brought into confined spaces. 2. Fire Prevention a. Permanent welding locations shall be in non- combustible booths painted with a flat black paint and provided with air circulation at floor level. A "Permit to Weld or Burn" is required at all other locations. b. Flammable materials shall be moved to a safe position away from the work area (thirty to forty feet), or are covered with non-combustible paper, blankets, canvas or other fire-resistant material. c. Floors and roofs shall be cleaned before welding. Where necessary, wooden floors

8 8 of 13 shall be hosed down with water and kept wet during the operation. d. Openings between floors, buildings, or at roof level, shall be covered to prevent escape of hot sparks. Areas above and below shall be inspected and all moveable combustible materials removed and personnel assigned on the roof and/or below to watch for hot sparks. e. Welding equipment shall not be used in an area where sparks or flames could be a hazard, i.e. rooms containing flammable gases, vapors, liquids, dust or other easily ignited materials. f. The location of fire-fighting equipment, alarm boxes, and telephones shall be known in advance. In case of fire, Security and Fire Prevention Services shall be notified immediately. g. All welding operations shall be performed in an area free from fire hazards. However, when welding must be done in hazardous locations, extra precautions shall be taken and additional personnel assigned if necessary. h. If cutting and welding is done just below the underside of the roof, the area shall be inspected and cleaned and the roof shall be inspected and all moveable combustible materials removed and personnel assigned on the roof to watch for hot sparks. i. On overhead work, before starting to cut a piece of steel or iron, make sure it will not fall, or that sparks will not enter areas above the work where there is any possibility of starting a fire. j. The work area shall be surveyed carefully after completing work and before leaving the work area. When advisable, a man remains in the area to guard against fire. k. Tanks, drums and other containers being welded shall be free from fumes. Such containers shall be filled with water or other inert gases or materials to prevent an explosion. l. A gas fire shall not be extinguished until the source of the gas is turned off. 3. Safety Precautions a. Cylinders may be moved for short distances by tipping and rolling them on the

9 9 of 13 bottom edge, but shall not be bumped or dropped. Nor shall cylinders be dragged, rolled horizontally or slid. b. All gas cylinders, whether empty or full, shall be handled with extreme care. Sudden shocks to the cylinders shall be avoided. Empty tanks shall be marked "EMPTY" or "MT". Cylinders shall be secured at all times. c. Hot metal shall be marked 'HOT" with chalk or paint for the protection of other employees. d. Oxygen shall never be used as a substitute for compressed air. e. Cylinders, empty drums and barrels shall not be used to support work. f. Gases shall not be mixed or transferred from one cylinder to another. g. Ladders, scaffolding, and work platforms shall be firmly secured and inspected by the operator before use. h. The operator shall wear the following protective clothing: 1) Welding helmets or goggles a) Shade #5 filter lenses for light gas cutting and welding; with Mapp gas #4 shade is used. b) Shade #6 filter lenses for general gas cutting and medium welding; with Mapp gas #5 shade is used. c) Shade #8 filter lenses for heavy gas welding; with Mapp gas #6 shade is used. 2) Gloves, leather gauntlet, NP-8360A or flame resistant terry cloth gauntlet, NP Gloves shall be worn for all cutting and welding jobs except very light work. 3) Aprons - Leather or other flame proof materials. Aprons protect the operator from sparks and radiated heat. Pockets shall be avoided because of the spark hazard. 4) Leggings- fire resistant. Leggings shall be worn for very heavy work.

10 10 of Ventilation Provisions 5) Hard hats, NPSP-306 or 307. Hard hats shall be worn when danger from falling objects exists. 6) Low cut shoes with unprotected tops shall not be worn because of the spark hazard. 7) For overhead work, the operator shall wear: a) Capes or shoulder covers of leather or other flame proof materials. b) Skull caps of leather or other flame proof materials. c) Ear protectors - approved ear protectors or plugs listed in the Non Production Materials Code Group S. 8) Wool Clothing. Such clothing is not easily ignited and protects the operator from temperature changes. When cotton clothing is worn, it shall be chemically treated to reduce flammability. The operator's clothing shall: a) Be reasonably free from oil and grease. b) Not have pockets or trouser cuffs which may catch sparks. c) Fit tight at the neck and wrists. Collars and cuffs shall be buttoned. The provisions in this section are established on the following six factors in welding which govern the amount of contamination to which welders may be exposed: * Dimensions of space in which welding is to be done. * Number of welders. * Possible evolution of hazardous fumes, gases or dust according to the metals involved. * Atmospheric conditions.

11 11 of 13 * Heat generated. * Presence of volatile solvents. a. When welding must be performed in a space entirely screened on all sides, the screens shall be so arranged that no serious restriction of ventilation exists. It is desirable to have the screen so mounted that they are about two feet (2') above the floor unless the work is performed at so low a level that the screen must be extended nearer to the floor to protect nearby workers from the glare of welding. b. Local exhaust or general ventilating systems shall be provided and arranged to keep the amount oftoxic fumes, gases or dusts below the permissible exposure limits established by Federal or State regulations and Chrysler standards, or the latest threshold limit values of the American Conference of Governmental Industrial Hygienists. c. Where welding operations are incidental to general operations, it is considered good industrial practice to apply local exhaust ventilation to prevent contamination of the general work area and to protect employees' health. d. Individual respiratory equipment shall be well maintained. it shall not be transferred from one employee to another without first being washed and sterilized. e. Manufacturers' cautions pertaining of fluxes shall be carefully observed. f. Mechanical ventilation shall be provided when welding or cutting is done on metals. See Exhibits A, B, and C. g. All air replacing that withdrawn by exhaust ventilation systems shall be clean and respirable. ln circumstances where it is impossible to provide such ventilation, air supplied respirators or hose masks shall be used. h. Oxygen from a cylinder or torch shall never be used for ventilation. i. When burning or welding on, or using fluxes or filler metals that contain toxic or hazardous materials, the industrial Hygiene Department shall be contacted for special instructions. j. Employees assigned to welding shall be instructed in compliance with the OSHA Hazard Communication Standard regarding hazards associated with their work.

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