Document eyE14egbMdYL7YOw1QGD4njy

Meeting (rtespfr06ry Air Standards Consistenttv'and Economically Where human health and safety are concerned, there is a need for equipment that can deliver respiratory air of a quality that meets or exceeds all applicable breathing air standards. By J. T. Vanchuk, CRSP. VicePresident. Robbins Aviation. Inc.. Vernon. CA. Purification of compressed air must be accomplished economically even though excessive amounts of contaminants, such as oil vapor, organic vapor, acid gases, particu lates. moisture, etc., may be present in the input air. When providing life support to people working in poten tially hazardous environments, one cannot risk installing and operating a compressed air purification system without assurance the equipment selected will perform efficiently. safelv. and economical!}--producing a product that consistently complies with accepted standards, practices, and regulations. In genera), those charged with the responsibility of providing pure compressed air for respiratory pur poses have approached the problem with good intentions and a sincere desire to resolve the problem consis tent with safety, economy, and efficiencv based upon the information available to them at the lime. For varied reasons, unfortunately, noi everyone has attained these objectives. Attempts to adapt exist ing compressed air systems used for Editor's Note: Mr. Vanchuk was vicepresident at Robbins Aviation at the time (his material was prepared. non-respiratory air applications to fill the needs for breathing air have encountered impediments that pre clude the production of pure breath ing air on a sustained basis. Usually, low pressure {100 to 150 psig or 340 to 510 kilopascals) plant air systems are used to power production or maintenance equip ment, and, in some cases, a lubricant is added to the air stream. In most cases, the air stream contains a high quantity of moisture. Sometimes instrument air lines are tapped because it is recognized that this air must be relatively free of oil and moisture. The usual approach to providing respirable air from a breathing equipment system is to tap off a line from the low-pressure distribution system of choice {100 to 150 psig or 340 to 510 kilopascals) and route the air through a series of filters and sorbents and class the effluent air as respiratory quality air. Filters and sorbents on air streams of low pressure and high velocity soon become ineffective and if an air quality assurance program is fol lowed it becomes quickly apparent that the spent sorbents and filters must be replaced on a basis of high frequency with the associated costs and expensive downtime. A well-designed purification sys tem must handle the maximum flow and pressure of the compressor consistent with providing adequate dwell-time of the air in the purifica tion media to permit optimum removal of the entrained contami nants. including moisture. Respiratory Air Standards The respiraton air standards, cur rently in effect were established by the Compressed Gas Association and have been adopted bv OSH A. NIOSH. ANSI, and NFPA. A new Purity of Compressed Air standard recently developed by the Canadian Standards Association has been adopted in Canada. For detailed information, please refer to: Com pressed Gas Association Pamphlet G-7 Compressed Air for Human Respiration': Compressed Gas Asso ciation Pamphlet G-7,1 Con\modiiv Specification for Air: Canadian AIR QUALITY According to CFR 1910.134 (d) Compressed air, compressed oxygen, and liquid oxygen used for respiration shall be of high purity Oxygen shall meet the requirements of the United States Pharmacopoeia for medical or breathing oxygen. Breathing air shall meet at least the requirements of the specification for Grade D breathing air as de scribed in the Compressed Gas Association Specification G-7.1P July 1978, NATIONAL SAFETY NEWS 8 AI... 0 0 0 / O I 63 Standards Association Standard Z180.1 Compressed Breathing A ir.3 The accepted breathing air quality standards are basic minimums and when contemplating the installation of an air purification system or pack age, consideration must be given to the removal of contaminants in addition to those spelled out in the applicable standard. For instance, should a plant require purified compressed air. yet the ambient air to be compressed contains contami nants, such as hydrogen sulfide, chlorine, vinyl chloride, acryloni trile. etc., it is not sufficient to com ply with the accepted breathing air standards; it is essential to assure oneself (hat contaminants not speci fied in the respiratory air standard be removed to a specified level, e.g., non-deiectable or to one-half the action level, throughout the service life of the purification media. Moisture is a major contaminant that is sometimes ignored or treated lightly. Excessive water vapor in compressed respiratory air is as much a contaminant as is excessive oxygen, though for different rea sons. Water vapor can condense due to low ambient temperatures and pressure drops caused by the expan sion of the air. Condensed water may turn into ice and affect valve and regulator operation. It will also cause internal corrosion of purifier chambers, storage vessels, distribu tion pipeline .systems--an undesira ble result from any stand-point. Damp, dark compressed air lines and storage vessels are ideal envi ronments for growth of micro-orga nisms. so it is essential for the protection of the human respiratory svstem that compressed air be dried prior to storage and distribution. The most efficient adsorbents used for removing oil vapors and noxious gases have a high affinity for water, hence, it is impossible to prevent sorption. Oil vapor and noxious gases cannot be removed without removing the water vapor as well. In addition, the elimination of carbon monoxide is usually accom plished by catalytic oxidation to carbon dioxide and a catalyst ordi* 64 narily used for this purpose requires the compressed air be exceedingly dry (a moisture content no greater than --50 F or --10 C dewpoint). Because of the foregoing reasons, we believe that the breathing air stan dards should be specific on the permissable moisture content (--65 F or --18.3 C dewpoint) and that contaminants other than those listed in the respiratory air standards shall not exceed the odor threshold or Vm the threshold limit value docu mented by the American Confer ence of Government Industrial Hy gienists (ACGIH). Purchases of compressed air pu rification equipment are often made on the basis of "low bid." This can prove disastrous and costly. Anyone who buys respiratory air purification equipment that is not properly engi neered to remove contaminants con sistently to the levels specified in the accepted standards and the purchas er's own specifications for air purity. is taking an unnecessary risk. There, is the impression that puri fication of compressed air can be accomplished simply by placing cer tain sorbents in pressure vessels and assembling them into a train down stream of the compressor. This is not true nor should it be acceptable to any prospective purchaser of an air purification system. The purchaser should prepare and issue detailed purchasing specifica tions and should demand that the manufacturer of such a system have proven capability in this highly specialized field. Numerous cases are documented where people have been hurt or killed by contaminated compressed breathing air. This need not happen, but it does with an ever increasing frequency. Solving the Problem By compressing the air to the The breathing air processing station at the New Orleans' Fire Department has an RAF compressor/purification unit plus downstream high pressure pure air storage tanks. -OL 000 July 1976, NATIONAL SAFETY NEWS 2,800-5,000 psig (9,520 to .17,000 kilopascals) range, processing it through a properly engineered pu rification system, and storing it in clean, high pressure storage vessels for subsequent use in self-contained breathing apparatus, or regulating the pressure so the air can be used with a clean low pressure distribu tion network, most of the problems we have discussed can be minimized or even eliminated depending upon the care the entire breathing system is given. We recommend high pressure purification because research and more than 30 years experience have proven that the most efficient and economical way to purify com pressed air consistently, is to squeeze the contaminants, including mois ture, out of the air stream by using high pressure in the purification train. Use of high pressure compressors will tend to force most of the mois ture and condense some gases and vapors out of the air stream during the compression process. These con densates are then drained off from the compressor sumps and permit a relatively dry compressed air stream to be presented to the purification system, enabling the sorbents to operate at optimum efficiency in purifying the compressed air for human respiration. When using ihis proposed high pressure purification package, distri bution line pressure drops will not occur when the pressure in the high pressure storage vessels of appro priate volume is in the range of 2.800 to 5,000 psig (9,520 to 17,000 kilopascals). Located between the dis charge side of the storage vessels and the distribution pipeline system is a pressure regulator of proper pres sure rating and flow capacity. The stored high pressure air is regulated down to 80 to 100 psig (272 to 340 kilopascals) and flowed into the breathing air distribution network, maintaining an even flow and work ing pressure. The automatic hi-lo pressure switch on the compressor is designed and installed to sense a pressure drop of 200 to 300 psig (680 to 1020 kilopascals) in the high pressure'' storage vessels, transmitting a signal to start the compressor to bring the storage vessel pressure back up to the designed working pressure and volume based upon the projected maximum breathing load. Another point that the designer of a breathing air distribution system should consider is having sufficient compressed breathing air stored in a storage vessel to enable a crew of employees to operate in complete safety, assured that they have a reli able supply of safe, pure breathing air for at least a four-hour period. This is necessary in case the atmo sphere is toxic and an orderly, prop erly sequenced process shutdown is required, or in the event the breath ing air package is down for mainte nance, or a power outage occurs shutting down the compressor. Work can continue to an orderly, safe conclusion, or the crew can escape to a fresh air base without panic or agita tion knowing that they have an ample supply of pure breathing air. The Compressor There is no such thins as a "breathing air" compressor. A com pressor by itself will not likely be able to compress breathing quality air. Assuming an "ideal" compressor, one that will not. by virtue of its operating characteristics, add con taminants during compression--the air it delivers will be of no better quality than the air it lakes in and compresses. However, all of the contaminants initially present in the ambient air are now present in the compressed air in concentrated form. A filter in a compressor will only remove some particulates and sus pended liquids. Filters will not remove oil vapors, organic vapors, acid gases, carbon monoxide, etc. Therefore, a compressor equipped with a filter (either intake or discharge), is not a "breathing air" compressor. Sometimes it is assumed that water lubricated compressors are "breathing air" compressors because the air is being "washed" as it passes through. This "washing" process will only remove particulates in the one to two micron range and, in some cases, with an efficiency as low as 65 per cent. If the seal water contacting the compressed air is not potable, then it is possible to add contamination to the compressed air. Potable water in an industrial complex is expensive and not always readily available to the site, of the compressor. It is not likely that any type of compressor using mechanical filtra tion or a water seal alone can produce compressed air to comply with the accepted breathing air stan dards. Compression, purification, and storage/distribution are separate steps of a process and one alone can not produce compressed air that is pure enough to intentionally put into people's lungs. To produce compressed air. con sistently and economicalh complxing with the accepted breathing air standards, an air compressor must be used in conjunction with a prop erly engineered purification train and storage/disiribuiion facilitv so that the owner mav be assured of operating safely, efficiently, and realize a return on his investment. Step One--Compression Compression makes it possible to store air in a reduced space, but more importantly, it prepares the air for purification. This is accom plished in part by "squeezing out" the contaminants--as in wringing out a wet sponge. Our experience has shown that the most economical pressure for purifying compressed air to acceptable purit\ levels (or better) is in the range of 2.800 to 3,500 psig (9,520 to 11.900 kilopas cals). For this reason, it is important that the compressor have a working pressure rating of no less than 3.000 psig (10,200 kilopascals). The compressor should be . equipped with an intake filter, auto matic stop-start pressure switch. July 1978, NATIONAL SAFETY NEWS Al.. 00005 /u 65 I Shown is one part o< the breathing air processing station at the Los Angeles City Fire Department--the compres sor/purification unit. The compressor prepares the air for purification the removal of all harmful matter. high air temperature shutdown switch. low oil level or pressure shut down switch, pressure gages, and an automatic drain system on the condensate traps. In keeping with good design, the compressor should be equipped with interstage and after-coolers along with pressure relief valves. In selecting the size and type of compressor that will be used with a breathing air system ask these basic questions: What is the application? How mans standard cubic feel of air will be needed per shift, week, month or year? What is the real need? How much space is available to house the compressor? What is the cost per square foot of floor space allocated to the breathing air system? Should one central system be designed or should several smaller capacity compressors be installed at strategic locations throughout the plant or building? Step Two--Purification Purification is the removal of all harmful matter. What matter is classed as harmful depends upon the end use of the purified air. In the case of compressed air for human 66 respiration, purification is an overall process, which consists of removing from the air stream particulates, mists, liquid contaminants (water and oil), organic vapors and gases, acid gases, hydrocarbons, carbon monoxide, other noxious materials and eliminating odors to recognized acceptable levels of breathing air purity. Anything less is NOT purifi cation. While filtration is a vital phase of purification, filtration alone will not make compressed air safe for human respiration. Correct location of the compres sor contributes significantly to effi cient operation of the entire air purification system. The compressor should be bolted to a flat, level surface in a covered area with ample space around it for good ventilation and general accessibility for ease of maintenance. The ambient tempera ture should be as cool as possible-- though never below freezing. Equal ly important is the selection of a good environment for the compres sor intake, which should be posi tioned so that the air drawn in is as clean as possible. This means that the intake must be above floor level--preferably eight feet (2.4 met ers) or higher--and well removed from all possible sources of ambient contamination including contami nants from neighboring operations. The intake should be equipped with suitable filters for particulates and if located outdoors the inlet must be hooded to keep out windblown dirt, insects, birds, snow, and rain. Purification systems for respirato ry air must include all of the equip ment necessary to achieve optimum purification of the compressed air so that it consistently meets the mini mum accepted air quality standards. Primarily, the purification system must consist of a mechanical device to remove liquid water and oil. a filter for solid particles, a device for removal of water and oil vapors, noxious gases, including carbon monoxide, and odors. A dewpoint of at least --65 F or --121 C (atmo spheric) or lower should be main tained consistently in order to permit the sorbents to function at optimum levels. Excessive moisture encountered during the air purification process can cause some contaminants that have been adsorbed to be displaced and flow downstream. In addition, moisture in a purification system may cause corrosion, which is extremely harmful to the inside of air receivers, control valves, and regulators. To ensure safe, efficient performance, the purification sys tem should also have inlet and outlet shutoff valves, a system bleed valve, a pressure gage, a relief valve, as well as a visual or audible method to indicate the need for renewal of the purification media. Highly desirable is an automatic drain system for waste liquids. The need, or desirability , for all of this equipment might be questioned and it is a fallacy for anyone to maintain that (he more accessories the better, or safer, the unit. Each item must make its own specific contribution to the overall opera tion. If it does not. then it should not be included. Converselv. it would not be prudent to attempt to operate without any item that does play a part in ensuring operating safetv. efficiency or the quality of the effluent air. As a mailer of policv. we do not recommend truck mounting respira tory air purification equipment. Taking a mobile air purification package to a fire, or other emergen cy. is extremely hazardous because many toxic gases not readily identifi able are produced during combus tion or mixing of chemicals and mav severely tax the capability of the purification system especially if the sorbent life was near its end-point at the outset of the emergency. In addi tion. it is not good practice to permit a compressor to ingest high concen trations of corrosive or potentially flammable gases or vapors. Sorbents for air-purification svstems should exhibit the following properties:'1 1) Activity or ability to .sorb the contaminants at a high rate: ( 2) Capacity or ability to sorb appreciable quantities of the con taminant: '> i-'i I... 0 0 0 0 f.:i 7 0 2 4 July 1978, NATIONAL SAFETY NEWS Storage and distribution systems 1) The analysis must cover the for breathing air must be designed, entire spectrum of allowable con sized, and installed with meticulous taminants listed in the applicable care ensuring that the hardware standard or regulation. selected will not corrode internally or off-gas, thereby defeating the entire purification system. The new Canadian Standard Z180.1 includes a complete section describing the design, material selection and fabri 2) The analysis must include the contaminant of special interest if it is not named in the applicable stan dard or regulation, i.e., vinyl chlo ride. acrylonitrile, etc: cation of storage and piping systems 3) If the air analysis indicates fail used for respirable air. ure in a single component, then the The fill station--for filling the portable cylinders with compressed and puri fied air for breathing--is part of the air processing equipment of the Los Angeles City Fire Department. 3) Retentivitv or ability to retain the sorbate once it has been sorbed: 4) Hardness or ability of granules to retain their size and shape when subjected to crushing and abrasion: 5) Stability or abilitv to retain these properties under norma] con ditions of storage and use. Subjecting purification media, vessel*, and piping to the rigors of shock and vibration created by transporting a purification unit at highway speeds over rough terrain Good practice dictates that high standards of cleanliness must be observed throughout all phases of air purification. Leak checking should be a continuing practice and done with an inert leak detector. Soapsuds, for example, should NEVER be used. Ambient air-borne contaminants can enter a pressurized system through loose connections or even through minute pinholes in vessels or tubing. Water vapor contamina tion of pressurized "dry" gas systems is a surprisingly common occur rence. Many people erroneously subscribe to the premise that "The pressure inside is greater than that on the outside, hence, nothing can get in"--a premise that is not alwavs true. Diffusion of a gas molecule from a region of high concentration to a region of low concentration is an established fact and the phenome entire sample is considered as having failed and does not comply with the applicable standard: 4) For ease of interpretation, analysis reports must be in the language and form common to the field of respiratory protection and industrial hygiene. Occupational safety and health regulations clearly indicate (he mini mum quality of compressed air for human respiration acceptable to a specific jurisdiction. Despite all the efforts and good intentions to insti tute and administer an approved program of respiratory protection utilizing self-contained breathing apparatus or air-supplied respira tors. the program could be placed in jeopardy if the compressed breath ing air is shown to be below the accepted minimum standards.fi to the scene of an emergency does non is described in Fick's Law." not constitute normal conditions of Breathing air distribution systems storage and use. The recommended can become contaminated down practice is to install permanently, the stream of the primary purification air purification package and move system, and therefore good practice air cylinders to the use-point to meet would indicate that a secondary the demand for breathing air. purification tower be installed on 1. Compressed Air for Human Respi long pipe runs or branch lines of a ration, CGA Pamphlet G-7. Compressed Storage--Distribution Once compressed and purified, breathing air distribution network. If there is any reason to suspect that any portion of the air purifica tion network has become contami Gas Association. 500 5th Ave.. New York 10036. 2. Commodity Specifcation for Air. CGA Pamphlet G-7.1. ibid. the air is generally stored in a large stationary receiver, or cascade sys tem of sufficient capacity to satisfy nated. that portion and everything downstream must be completely disassembled and thoroughly 3. Compressed Breathing Air. Stan dard 2180.1. Canadian Standards Asso ciation. 178 Rexdale Blvd.. Rexdalc. Ontario. Canada M9W 1R3. the end use under normal and emer gency operating conditions. For ob cleaned using the proper proce dure. 4. Respiratory Protective Devices. 1963. American Industrial Hygiene As vious reasons, receivers or cascade Regulations and standards refer sociation. 66 S. Miller Rd.. Akron. OH / cylinders should be used for the to testing or analyzing the breathing 44313. storage of PURIFIED AIR ONLY air to determine compliance with the 5. Bird. R.B.. W.E. Stewart, and E.N, and should never be filled directly applicable standard or regulation. Lightfoot. Transport Phenomena. 1960. from the compressor, by-passing the These points should be kept in John Wiley & Sons. 605 Third Ave.. purification stage. mind: New York'l 0016. p. 502. July 1978, NATIONAL SAFETY NEWS SAL 0000570;:.;;:-: 67