Document 0LkbZ0m1r0j5O4VLznGVyNXVm

42--Flammable and Combustible Liquids monoxide, benzene, hydrogen sulfide, and tetraethyl lead hazards (This last instrument is available from suppliers of tetraethyl lead ) Loading and Unloading Tank Cars Only framed employees should load or un load tank cars containing flammable liquids These men should understand the danger of possible fire and explosion and of asphyxia tion from breathing flammable vapors As an added precaution, unloading and pumping operations should be discontinued during electrical storms Invoices and shipping papers on incoming tank cars should be checked closely for corre spondence with actual tank car numbers and, in doubtful cases, contents should be tested in order to prevent accidental mixture of flam mable liquids in plant tanks See Fig 42--7 for typical tank car construction details Spotting cars A car movei should be used, if it is neces sary to hand spot a car The worker should stand with the handle of the bar to one side of the hack rail and face the car with his feet well apait so that he cannot be overbalanced easily After the cai is spotted, with the dome out let opposite the loading or unloading line, the brakes should be set and the car wheels blocked The "blue flag" stop sign (at least 12 by 15 in , with words such as Stop--Tank Cab Connected or Stop--Men at Wobk) should be set before loading lines are con nected or woik is done on the car The sign should be located about 25 ft ahead of the car toward the main line, so train crews cannot come onto the track without seeing it (Full details are given in Chapter 28, "Elevators and Plant Railways ") The siding should be bonded and grounded for protection from stray electrical currents (Fig 42-8) Usually, the spur tiack installa tion would be made or supervised by the serving railroad For applicable specifica tions, the reader is referred to the Association of American Railroads Signal Manual of Rec ommended Practice (See "References ") The relative location of electric power fines to the tank car unloading position is an im portant matter discussed in the AAR Bureau of Explosives Circular No 17-E, Recom mended Practice for the Prevention of Electric Sparks That May Cause Fires in Tanks or Tank Cars Containing Flammable Liquids or Flammable Compressed Gases, Due to Prox imity of Wire Lines Its pertinent provisions include the following (A) Ceneral 1 Where any electric power fine is within 20 ft of the tank opening, the use of a me tallic gaging rod is prohibited (B) Location of Tanks or Tank Cabs 1 Wheiever possible, stationaiy tanks shall not be located under or near any electric power lines 2 When the contents are being gaged oi tiansfened, tank cars, wherever possible, shall not be located iindet or near any eleetuc power lines 3 Wheie tanks or tank cars (the contents of which aie being gaged or transferred) are necessarilv located under or near power lines having a span length of 150 ft or less and operating at a voltage not exceeding 550 volts between conductors, the follow ing rules shall be observed a Where power lines pass overhead, there shall be a minimum vertical clearance of 8 ft at 60 F between the wues and the tank b Where power lines pass neaiby and do not have the minimum vertical clear ance specified in paiagiaph 3-a, theie shall be a minimum horizontal clearance of 8 ft between the wne lines and the tank c Openings m tanks shall be at least 6 ft distant, measured horizontally from any overhead power lines 4 Where tanks or tank cais (the contents of which are being gaged or transfeired) are located under or near power lines having a span length m excess of 150 ft or operating at a voltage in excess of 550 volts between conductors, it is recommended that special studies be made by qualified persons and such additional clearance provided as is necessary to give adequate protection 1298