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Why? Survivinga Steam Rupture

By WAYNE KIRSNER, PE,Kirsner Consulting Engineering, Inc.,Atlanta, you hear waterhammer bangingor popping noises, look for an is nota normal oracceptable part of Steam systemoperation. Steam should be isolatedfrom the hammering pipe section andthe section drained of condensate.(See Condensation-Induced Water-hammer, January 1999, HPAC Engi-neering.) But, if you must be in a utili-dor or manhole, observe the steamdistribution piping around you. Visual-ize your path of escape. Be wary of castiron valves and traps, corroded con-densate lines, flexible expansion joints,and gasketed blind flanges (the gasketscan blow out from between theflanges). Try to stay between the exitand these elements if you anticipatethe possibility of waterhammer. Alwaysanticipate waterhammer during startupof cold Steam WATERHAMMER STRIKESIf waterhammer strikes and rupturesa high-pressure Steam or condensateline entrapping you:1.

receive are confined to your skin, how-ever, you have an excellent chance of recovery. In a 1981 study of 1914 burn patients, only 7 percent of those with

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Transcription of Why? Survivinga Steam Rupture

1 By WAYNE KIRSNER, PE,Kirsner Consulting Engineering, Inc.,Atlanta, you hear waterhammer bangingor popping noises, look for an is nota normal oracceptable part of Steam systemoperation. Steam should be isolatedfrom the hammering pipe section andthe section drained of condensate.(See Condensation-Induced Water-hammer, January 1999, HPAC Engi-neering.) But, if you must be in a utili-dor or manhole, observe the steamdistribution piping around you. Visual-ize your path of escape. Be wary of castiron valves and traps, corroded con-densate lines, flexible expansion joints,and gasketed blind flanges (the gasketscan blow out from between theflanges). Try to stay between the exitand these elements if you anticipatethe possibility of waterhammer. Alwaysanticipate waterhammer during startupof cold Steam WATERHAMMER STRIKESIf waterhammer strikes and rupturesa high-pressure Steam or condensateline entrapping you:1.

2 Don t panic. Your first imperativemust be to avoid inhaling hot Steam it can burn your throat and lungs. In-halation injury is the number onecause of fatalities in burn Youmay have gotten sprayed with hot con-densate if you were near the condensate can be no hotter than212 F at atmospheric pressure, and gen-erally, if it s under pressure, flashingwill cause the condensate stream to en-train air to cool , ex-posure to water at 156 F for over onesecond will scald you. If the burns youSurvivinga Steam Rupturein an Enclosed SpaceAt BrookhavenNational Laboratoryin 1986, four menworking in a utilityvault were engulfedby Steam whenwaterhammer blewout the gaskets inthe Steam main. Two men died; two survived. Why?In the January 1999 HPAC Engineering article Condensation-Induced Wa-terhammer, Wayne Kirsner wrote about workers trapped in an undergroundutilidor during a Steam accident and how they escaped.

3 In July 1995, HPACE ngineering published What Caused the Steam Accident that Killed JackSmith also by the author about a Steam fitter who died under two feet ofhot condensate when a Steam valve he was opening blew up in his F condensate emerging from a 1 8in. ori-fice cooled to 152 F after 20 in. of travel in 80F ambient air (see first sidebar).Heating/Piping/AirConditioning July 199939 HPACENGINEERING receive are confined to your skin, how-ever, you have an excellent chance ofrecovery. In a 1981 study of 1914 burnpatients, only 7 percent of those withno inhalation injury died. The mortal-ity rate for those with inhalation injurywas 55 Evacuate an isolatedmanhole assoon as possible. If the pit is heating up orfilling with hot condensate and there isno alternate escape route, it s a better betto evacuate quickly even if it meanspassing through a saturated Steam jet than risking inhaling hot Steam and airduring an attempt to reach an alternateexit (see sidebar on this page).

4 This advice was borne out in a 1986steam accident involving four workersat the Brookhaven National Labora-tory. Two Steam fitters were standingside-by-side in an isolated manholewhen a waterhammer blew out the gas-kets from two 10-in. blind pipe man darted through the escapingsteam and condensate to the exit lad-der behind him. He emerged with sec-ond- and third-degree burns, but fullyrecovered, and today is a constructionsafety specialist at Brookhaven other man attempted to crawl be-neath the pipes to the exit ladder onthe opposite side of the manhole. Hebecame disoriented and took severalminutes to emerge during which timehe was forced to inhale hot air andsteam. He died the following day withburns over 75 percent of his If the manhole is not isolated, con-sider trying to move away from the siteof the leak through tunnels to other ex-its.

5 Cooling air should be drawn fromthe direction of other openings due tothe draft caused by Steam and hot airexiting the open manhole above theaccident site. Remember, your fellowsteam fitters heard the KA-BOOM! of the waterhammer, and everyone inthe area will have been alerted to theaccident by the Steam plume billowingout of the manhole. Your co-workers first instincts should be to isolate thesteam main to stop the Steam second thought should be toopen alternate means of egress for additional openings will let freshair enter the utilidor and keep thesteam traveling up and out of the man-hole at the accident GROUND RESPONSES team fitters/operators respondingto the accident have three tasks tocarry out without delay: Isolate the Steam leak and vent thesteam main. Open alternate means of egress andallow air into the utilidor.

6 Call 911 and inform them that youmay have one or more third-degreeburn RUPTUREHOW DANGEROUS Is a High-Pressure Steam Jet?Being sprayed with high-pressure Steam can be less serious than contact withhot water even though the Steam may initially be hotter. A jet of high-pressuresteam spraying through a crack or small orifice at high velocity expands andentrains the air surrounding it. If the air is cool, it rapidly dilutes the temperatureof the Steam a series ofexperiments reported in ASHRAET ransactions, 1966, 300 F saturatedsteam spraying from a 1 8in. diameterorifice into 80 F ambient air cooled to106 F after only 15 in. of travel4 coolenough to stick your hand in. The rate ofcooling was insensitive to a confined space, however, even asmall Steam leak will warm thesurrounding ambient air theambient air heats, its temperature-diluting effect on the Steam jet isdiminished.

7 This is one big reason whysteam ruptures in confined spaces,especially warm confined spaces, aremuch more dangerous than those inopen spaces with good air reason is that Steam permeatesthe space quickly. Condensing Steam has a high heat transfer coefficient. Thismakes it a penetrating heat. Below 12 percent Steam by volume in a Steam -airmixture, the condensing temperature of Steam is below 120 F. Thus, steamcondensing on your skin deposits condensate at a temperature below 120 F.(The pain level for most people as well as the temperature at which the hotcondensate will start to burn you is 120 F.) Thus, Steam hotter than 120 Fremains a gas, which is relatively benign since it has a very low heat transfercoefficient. You can withstand dry Steam and air temperatures above 200 F. Asthe percent of Steam (by volume) in the air surpasses 12 percent, as it willquickly in a confined space, the condensing temperature rises above 120 120 F, condensing Steam will above facts suggest different courses of action for escape from isolatedmanholes versus utilidors connected by tunnels.

8 Isolated manholes must beevaluated immediately. It also suggests that forced ventilation of confinedspaces can save lives in the event of a Steam cools the jet somewhat. I calculate Isentropic Expansion to Mach 1 at .58 Pocoolsthe gas 5 percent of its Rankine temperature. Non-isentropic expansion from .58 Poto Pexitwillcool it somewhat cooled to 12 percent of its initial temperature difference at 15 in. from the nozzle forsteam pressures between 50 and 142 100 psig Steam leak through a 1 4in. orifice would warm 1000 cfm of air from 80 to 200 Fin as little as 30 in. pipe emitting 18 ft long jet of 115 psig saturated Steam . Hand is 15 1999 Heating/Piping/AirConditioningSPECIFIC INSTRUCTIONS TOTHOSE ISOLATING THE MAIN: Open manhole covers at adjacentmanholes to allow cool air to be drawninto utilidors.

9 If your co-worker is trapped,this may save him. Isolate the Steam main as close to thesite of the accident as possible. Shuttingdown the Steam at the boiler plant is okay,but it will take longer for Steam mains toempty of Steam . Isolating and ventingclose to the accident is best, if there s nounreasonable delay. Vent the isolated section of steammain to relieve the Steam pressure openthe bleed valves and trap If a co-worker emerges from a Steam pitwith second- and third-degree burns,you ve got two imperatives after calling forprofessional medical care: keep the woundsfrom being exposed to infection, and treatfor shock. Specifically: Peel off clothes soaked with hot conden-sate if still scalding hot exceptwhere cloth-ing is involved in open wounds. Lay the victim down and, assuming noevidence of spinal injury and no discomfort,elevate his feet about 1 ft to treat for shock.

10 Ask if his throat or airways areburned. (If so, EMTs must be prepared tointubate should the victim s air passageclose off.) Advise the arriving EMTs. Get cool water, not cold or ice water,to apply to first and second degree burn ar-eas to reduce pain. Do not induce shiver-ing. Do not apply ointments. Do nottouch the wounds. Do not attempt to remove materialadhering to the ) Herndon, , Thompson, Tra-ber, Crit. Care Mar 1(1):79:96 Pul-monary injury in burned ) Crit. Care Jul: 9(7) ) Brookhaven Accident Report and telecomwith Alfred W. ) Armstrong, and Harris, Temper-ature Distributions in Steam and Hot Water JetsSimulating Leaks, ASHRAE Transactions, 1966,pp. 147-156, and Erwin Hansen, Hydronic Sys-tem Design & Operation, 1985, pp. , I M ALIVE SAGA OF A Steam ACCIDENT SURVIVORC onventional wisdom held that Arland Dean Stackpole had a one-in-threechance of survival.


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