Transcript
Section 10: Compressed Air Safety OVERVIEW Compressed air is air under pressure that is used to power mechanical devices. This section provides information about the hazards involved with compressed air and the associated safe work practices. It also contains information about pneumatic tools and compressed air systems.
Commented [JG1]: http://www.webbikeworld.com/t2/compr essed-air/
HAZARDS OF, AND SAFE WORK PRACTICES FOR, USING COMPRESSED AIR Compressed air is not "just air." Compressed air is extremely forceful and dangerous. Equipment that uses compressed air can emit it as a focused stream of air driven at a high velocity, which can cause serious injury or death to its operator or persons in the immediate area if not properly controlled. Air pressure as low as 12 pounds per square inch (psi) can blow an eye out of its socket. Compressed air blown into the mouth can rupture the esophagus or lungs. It is possible for compressed air to enter the blood stream through a break in the skin and cause an embolism, leading to death once it reaches the brain. Compressed air can also rupture an eardrum from inches away. Compressed air at 30 psi is forceful enough to dislodge scale from piping. It can blow debris around with the force of shrapnel. Compressed air has a way of blowing dust and particles of all shapes and sizes around a work area, regardless of what you’re using the compressed air to do, creating a respiratory hazard. The exhaust of a compressed-air-powered tool is LOUD(!) and must be muffled to prevent injury from noise, or hearing protection must be worn. Air blasting from an uncontrolled compressed air hose can cause the hose to whip-around and injury you. The outlet piping of an air-compressor can be very hot and can cause “contact burns” or fire. Compressed air equipment can have internal pressure tanks that can remain energized even if the compressed air is shut off to the equipment. These tanks must be bled to atmosphere when the equipment is worked on to ensure safety. Therefore, it’s important for you to understand the uses and hazards of compressed air
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to ensure your safety when working with it, or when around others who are using it in their work.
Flammable / Explosive Locations Because compressed air generally has no flammable materials or sparks associated with its use, in locations where flammable atmospheres are a hazard it is often used for conducting safe work. Such locations demand that piping and equipment used to deliver the compressed air must be made of non-sparking materials such as brass or bronze. In addition, plastic and other materials that can develop static charges must be attached to “ground” using grounding / bonding straps so no static electric discharge can occur causing an explosive spark.
Physically Restricted Locations Compressed air driven motors, blow-off nozzles and other associated equipment are quite small in size when compared to electric or hydraulic motors. As such, they may be chosen for use in locations that have small spaces or are somehow physically restrictive. Care must be taken to pipe exhausted compressed air gas away from the work location, and muffle the air sound to reduce potential noise hazards.
Cleaning Compressed air is often used for cleaning, though this practice is dangerous and not recommended. Compressed air can blast particles air-borne with injury-producing force. Air-borne particles can lodge in your eyes, go up your nose, enter your mouth and impinge your clothing or unprotected skin. In addition, airborne dusts can create an explosive atmosphere if dust is not controlled.
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NEVER USED COMPRESSED AIR TO CLEAN ANY PART OF YOUR BODY OR YOUR CLOTHING!
If compressed air must be used to blow-off materials for cleaning, then the nozzles used are required by
Commented [JG3]: http://www.wisconline.com/objects/MTL10202/MLT10202.htm
Never build and use your own compressed air nozzles! Only use nozzles built by manufacturers that are designed to limit nozzle force to 10 psi or less.
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CalOSHA to be limited to 10psi force available at the nozzle tip. There are many kinds of compressed air nozzles sold through industrial supply houses that have these built-in pressure limiting features in the design of the nozzle.
Vacuum Vacuums operated by compressed air “venturi tube” vacuum generators are an alternative to using compressed air blow-off nozzles for collecting dust, machine tailings and other shop particulates.
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They have no moving parts, are easily cleaned if they clog, and can handle particles of many sizes. They can be loud, so hearing protection must be worn when using them. They also can consume a lot of compressed air which can be costly to operations, but in certain situations such as cleaning machines and sucking up machine tailings, they are the tool of choice for safe work.
Commented [JG6]: http://techmarketinginc.net/holdfast/Ima ges/Hold%20Fast%20Vacuum%20Generator.jpg
Transport Compressed air can be used to transport heavy items using floating “pads” placed under the item and then the pad is pressurized creating a thin blanket of air the item then “floats” on. In addition, compressed air can be used to blow parts from one conveyor transport to another, or otherwise move materials through convective transport systems. Hazards include noise, dust, static build-up, etc… and PPE similar to other uses must be worn when working with compressed air in this capacity.
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Air Blow-off Nozzle for Transport
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Painting / Coating Applications Compressed air is often used for powering spray painters and other coating applications. Hazards in such situations can include pressurized tanks that can hold a compressed air charge even when the equipment has been disconnected from the air-source. In addition, aerosolized coatings can present an inhalation hazard, so respiratory protection must be worn. As with other compressed air uses, general hazards include noise, dust, static build-up, etc… and PPE similar to that used for other compressed air uses must be worn when working with compressed air for this use.
Inflation An obvious use of compressed air is to inflate things. Tires, airsprings, bellows, pillows, cushions, balls, etc. are all inflated using compressed air. Inflation hazards include mechanical hazards of getting trapped by an inflating object against an immovable object, over-inflation causing explosion if too much compressed air is added to a whatever’s being inflated, etc. Never reach into, place part of your body or stand between something being inflated by compressed air and an immovable object.
Powering Pneumatic Tools There are many different kinds of tools that are powered by compressed air. Pneumatic tools include air compressors and a variety of tool attachments. Wrenches , nail guns, drills, impact hammers, riveting guns and blow guns are common attachments. Some robotics operate on compressed air. Some tools are hand-held. Some tools have no moving parts, while others have motion such as rotation, sliding and reciprocation. Before using a tool operated by compressed air, ask your Supervisor for instruction on its safe use. If available, read the manufacturer’s “owner’s manual” to understand the safe-work practices to implement when using the compressed air tool. Assess your surroundings and work area for hazards such as combustible or flammable materials, nearby personnel, etc… and isolate personnel and remove unsafe materials before using a compressed-air-powered tool.
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Always conduct a pre-use inspection of any compressed air tool, air hose and fittings for damage, disrepair, or missing UC System - Shop Safety Reference Manual Section 10 – Compressed Air Safety
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parts. Make sure air hoses and fittings are securely tightened. If a tool fails the pre-use inspection, notify your supervisor and remove it from service by attaching a red tag that states “DO NOT USE.” Always wear eye protection and never point pneumatic impact tools, such as riveting guns, nail guns or hammering tools, toward a person. Turn off the air supply at the control valve and tool blade before disconnecting a pneumatic tool bit from the tool (unless it has quick disconnect plugs). Be especially careful when using pneumatic tools around fuel, flammable vapors, or explosive atmospheres. They can generate static electricity and must be grounded or bonded when these chemical hazards are present.
WHAT PPE SHOULD BE WORN WHEN USING COMPRESSED AIR? Because compressed air has a tendency to blow stuff around, eye or face protection must always be worn when working with compressed air. In high-dust producing operations, a dust mask may need to be worn. In addition, always protect as much of your skin as possible by wearing long-sleeve shirts, and long-leg pants, socks and shoes. If there’s a possibility of your hands contacting compressed air, wear protective work gloves, preferably made of leather or thicker rubber. If compressed air is used without a muffler installed on the outlet, or in air-hammering / impact tools, then hearing protection must be worn. And, when used to paint or apply coatings, respiratory protection may have to be worn. When compressed air is used to power tools and equipment that rotate or roll, then long hair must be tied-back and loose clothing removed or tied back. As with all shop equipment, it’s a safe-idea to remove any handjewelry, neck-jewelry and dangling ear-jewelry. Contact your EH&S department to get help in assessing your PPE needs for working safely with compressed air, and always wear required PPE when you use compressed air.
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COMPRESSED AIR SYSTEM Every compressed air system is comprised of eight primary parts: 1. An air compressor driven by a motor with… 2. An automatic start / stop switch operating on the receiver tank pressure, 3. An air receiver / accumulator tank with… 4. An over-pressure relief valve, 5. Possibly, an air pressure regulating device with shut-off valve to regulate systempressure connected to… 6. Air distribution pipes that carry the compressed air to the point-of-use, and 7. The filter / regulator / desiccator at the “Point-of-use” where equipment is attached to the air system, and 8. Drain valves located throughout for draining water and other contaminants.
A Typical Shop Compressed Air Distribution System (Diagram courtesy of Sharpe Inc.)
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Commented [JG11]: http://www.sharpe1.com/sharpe/sharp e.nsf/Page/Air+Piping+Layout
A Typical Air Compressor with Key Parts Shown
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Air Compressors and Receiver Tanks Ensure that your air receiver tank is equipped with at least one pressure gauge and an American Society of Mechanical Engineers (ASME) safety “pop-off” pressure relief valve. Use a spring loaded safety relief valve to prevent the receiver from exceeding the maximum allowable working pressure.
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Testing air receivers. Only hydrostatically tested and approved tanks may be used as air receivers. The only time the maximum allowable pressure of an air receiver can be exceeded is when testing it. Your campus’ Risk Services Department has contracts with pressure vessel testing engineers that will test your air receiver tanks and certify them as meeting their rated capacity. Contact your Risk Services Department to enroll your air receiver tanks to be periodically pressure tested. It’s required by law.
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Install air receiver tanks so they can be periodically inspected with the entire outside surface readily visible. Do not bury them or place them in hard to reach locations. The intake and exhaust pipes of small tanks must be removable for interior inspections. Tanks over 36 inches in diameter must have manholes. Inspection openings are sufficient for smaller tanks. Tanks with volumes of 5 cubic feet or less can have pipe lug openings for inspection.
Pressure Relief Devices Every receiver tank is required by regulatory code to have a pressure-relief valve installed on the tank. There are many different kinds of pressure relief valves in looks, but they all function much the same in that they are designed to vent an over-pressure condition inside the tank to atmosphere before the tank becomes pressurized beyond its design strength and could explode. Every pressure relief valve will have a clear label or tag that states the conditions the valve is made to operate in, and the minimum pressure the valve will start to relieve at. When you are conducting your first-use inspection, always check to make sure the pressure relief valve is clearly visible on the air receiver tank and unobstructed. It is usually located sticking out of the top of the tank with its own plumbing-port dedicated to it. Sometimes it will be “T’d” off of the supply piping coming out of the tank. Regardless of the piping configuration, through your inspection ensure there is no type of valve or other obstruction means installed between the interior of the receiver tank, and the pressure relief valve. Check the operating pressure label on the receiver tank, and that of the pressure relief valve setting, to ensure the relief valve is set to “open” and relieve pressure in the tank at a lower-pressure than the tank is rated for. Below are a number of different models of pressure relief valves. Always look for a relief valve properly installed on your compressed air equipment to ensure your safety.
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Commented [JG15]: http://www.generant.com/images/prod ucts/Vent-Relief-Valves.jpg http://www.watts.com/prod_images/hi-res/530C.jpg?r=1 http://www.aircompressorservicekits.com/images/P/SRV18725-PSI-02.gif http://bostonheatingsupply.com/watts0274836.aspx
Use ASME approved cast iron seat or disk safety valves that are rated and stamped for the intended service application and pressure range of operation. Commented [JG16]: http://usersites.horrorfind.com/home/h alloween/wolfstone/Pneumatics/pnuint_HF_36797.gif
Always install valves, gauges, and other regulating devices so they cannot be made inoperative or isolated from the receiver tank. Never position any kind of shut-off or stop valve on the air lines connecting the compressor with the receiver tank. If the design of a safety or a relief valve allows liquid to collect on the discharge side of the disk, equip the valve with a drain at the lowest point where liquid can collect, and frequently crack the drain valve open to drain any excess fluid from the system.
Commented [JG17]: http://www.northerntool.com/images/pr oduct/2000x2000/451/4519303_2000x2000.jpg
Pressure Regulation Devices When conducting your initial safety inspection of your equipment, turn the pressure regulator control knob counterclockwise to ensure the regulator valve is fully “off”. Then, after the compressor has been started and the pressure in the receiver tank has been brought up to normal operating pressure, turn the pressure regulator valve clockwise until the desired system operating pressure is reached on the pressure gage. When you have completed your work with the air compressor, reverse this process by turning the pressure regulation control knob counter-clockwise fully to reduce pressure in the distribution lines to zero.
Commented [JG18]: http://i01.i.aliimg.com/photo/v0/630998 433/Air_Pressure_Regulator_Adjustable_Regulator_Pneumati c_Regulator.jpg
Drains Consider the drainage issues associated with receivers as humidity in the air can condense inside the tank and cause the tank to fill with water and other “air borne” liquids. Fit air receivers and system pipe-drains with a drain cocks on the bottom of the receiver tank, and in drop legs in the system. Drain receiver tanks and system pipe drains frequently (at least every other day and daily in high humidity weather) to prevent accumulation of liquid inside the tank and piping. Receivers and piping having automatic drain systems are exempt from this requirement.
Air Distribution Lines Select air lines made of high quality materials with standard fittings and secure connections. Check hoses before use to make sure they are free of defects and properly connected to pipe outlets. Repair or replace defective equipment immediately. UC System - Shop Safety Reference Manual Section 10 – Compressed Air Safety
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Identify the maximum allowable operating pressures (psi) by tags or markings on the pipeline outlets. Air hoses are subject to damage and can become hazards. Avoid bending or kinking air hoses. Hose reels can help keep hoses under control while pressurized. Always secure compressed air hoses or in some way hold them from freely moving about. If a leak occurs or a hose gets severed, the hose can whip-around wildly and hurt you and others nearby. Keep air hoses free of grease and oil to prevent deterioration. Whenever possible, suspend hoses overhead for more efficient access and protection against damage, and to reduce tripping hazards.
MAINTAINING COMPRESSED AIR EQUIPMENT Keep equipment appropriately lubricated, while avoiding over lubricating. Do not use flammable lubricants on compressors, because they often operate at high temperatures that could cause a fire or explosion.
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Frequent cleaning with soapy water (e.g., lye solutions) is recommended to keep carbon deposits off of compressor parts. Do not use kerosene or other flammable substances to clean compressed air equipment. Be sure to purge air systems after each cleaning and prior to use. Frequently open and purge drains on compressed air system piping and tools making sure to stand clear of any drained materials.
TRAINING NEEDS You must receive the appropriate training for using compressed air and the equipment attached to it. This training will help you to understand the limits of the equipment you are using and know how to shut it off when necessary. Know the maximum allowable pressure of the compressor, and make sure that all pipes, hoses, and fittings exceed the pressure rating of the compressor.
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EQUIPMENT INSPECTIONS All components of compressed air systems should be inspected upon first use when setting up the equipment and starting a project, and regularly during use. This includes the air receiver tanks, pressure relief valve, air distribution lines, pressure regulation devices, and air compressors and their drive / motor components. Stop using any equipment that is found defective or needing repairs immediately. Red-tag defective equipment to prevent use, and alert the shop supervisor of needed repairs / replacement. Air Compressor Safety Guidelines 1. 2. 3. 4.
Make sure air intake is from a clean outside source. Use filters or screens to maintain clean air intake. Do not operate gasoline or diesel powered compressors indoors. When using equipment outside buildings, position exhausts so they are directed away from doors, windows, and air intakes. 5. Ground all exposed, non-current carrying, metal parts of a compressor. 6. Operate at manufacturer’s recommended speeds and pressures. 7. Keep equipment from overheating through adequate ventilation and/or cooling water. 8. Use guards on all moving parts, such as compressor flywheels, pulleys, and belts. 9. LO/TO the switches of electrically operated compressors during maintenance to prevent accidental starting. 10. Disconnect portable electric compressors from the power supply before performing maintenance. 11. Open and purge drains frequently (daily is recommended).
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[THIS PAGE LEFT INTENTIONALLY BLANK FOR DUPLEX PRINTING PURPOSES.]
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SECTION 10 QUIZ – COMPRESSED AIR SAFETY 1. Which type of injury can result from the unsafe use of compressed air? a. Blowing out an eardrum or eye out of its socket b. Ruptured Esophagus c. Air embolism in bloodstream d. All of the above 2. True or False? Personnel should use an air gun to clean their clothing and/or themselves from dry dust and debris. 3. What is the minimum PPE required when working with compressed air? a. Safety Glasses and Gloves b. Safety Glasses and Hearing Protection c. Safety Shoes and Gloves d. Hearing Protection and Safety Shoes 4. True or False? When performing maintenance on an air compressor, it does not have to be locked out and tagged out. 5. Which of the following are NOT part of a routine safety inspection conducted by personnel prior to first use at the beginning of a work-shift of a compressed air system? a. A periodic safety inspection of the receiver tank for structural problems. b. Sign of leakage of oils from motor or compressor. c. Missing or loose guards on drive belts. d. A missing or damaged pressure relief valve, or a damaged pressure gage on a receiver tank outlet. 6. True or False? Compressed air receiver tanks must be periodically inspected for structural problems by a licensed engineer hired by the Risk Services Department to ensure the tank is in safe working order. 7. True or False? Hand-held pneumatic tools sometimes have a small pressure tank in the tool that must be “bled to atmospheric pressure” before you can safely do maintenance on the tool.
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* Quiz Answers: 1. D 2. False – Never use and air-gun to clean yourself or your clothes off. Never aim an air-gun at another person. 3. B 4. False – Always conduct EI-LOTO on an air compressor when doing maintenance on the equipment. Air compressors by nature and design have multiple kinds of energy associated with their operation 5. A 6. True 7. True
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