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L'�)W,/Ll 1_� <br /> STAiim OF CAU FOR NIA J Pete Wilson. Govemor <br /> DEPARTMENT OF INDUSTRIAL RELATIONS <br /> DIVISION OF OCCUPATIONAL SAFETY AND HEALTH xsV + <br /> 45 Fremont Street, Room 1200 •ooaessAMY TO: ~ <br /> San Francisco, CA 94105 ; ! =i7 P.O.Box 420em <br /> sm1 Fruiasm.cr 94142 <br /> HAZARD ALERT <br /> This BULLETIN is to advise all agencies and contractors regarding the use of <br /> pressure-washing devices while cleaning the interior of an underground storage <br /> tank which has previously contained a flammable liquid. <br /> During a recent tank cleaning and lining operation utilizing pressure-washing <br /> equipment, an explosion ocali—red 'killing one employee and severely injuring a <br /> second. It is believed the pressure-washing operation not only stirred up residual <br /> sludge on the bottom of the tank releasing flammable vapors, but also ignited those <br /> vapors by the discharge of static electricity generated by the pressurized water <br /> striking the surface of the tank. <br /> The National Leak Prevention Association (NLPA) Standard 631, an ANSI <br /> Recognized National Standard entitled Ently. Cleaning`Interior I=ection Repair <br /> and Lining of Under, ound Storage Tanks, has recognized the use of such processes <br /> as a static electricity hazard. The NLPA has included a warning statement in Section <br /> A7-3 concerning the use of water spraying equipment The statement is as follows: <br /> "WARNING: Tank Cleaning which requires the spraying of water or steam into <br /> tanks should not be used as part of this standard. Water spray jets, water-hose <br /> streams, or steam can generate static charges at the nozzle and upon those objects <br /> which the water impinges. Grounding the jet nozzle will not prevent a static charge <br /> from being generated." <br /> If pressure washing is performed on the interior of storage tanks, it is imperative that <br /> the atmosphere be maintained below 10% of the lower explosive limit (LEL) at all <br /> times. If this LEL cannot be assured by purging, pre-flushing, inerting, or other <br /> means, no source of ignition shall be permitted in or near the storage tank. This <br /> includes the use of pressure-washing devices discussed in this alert <br /> Questions regarding this matter may be directed to Jerry Neisler, Senior Industrial <br /> Hygienist, at (714) 939-8611 or Ray Rooth, Senior Safety Engineer, at (714) 939-8479. <br /> July 15, 1998 <br />