NEAFC 31st Annual Conference.pdf - New England Association of ...

NEW ENGLAND ASSOCIATION OF FIRE, CHIEFS
In a 16 tt line operating at 750 psig the bursting pressure for each lineal foot is
72 tons..As the only force in opposition to this bursting are the two sidewalls of
or even less in thickness, it is easy to see why ruptures have occurred due to even
relatively minor changes in pipe stress. These have been attribut£d to a myriad of causes
including ~basic failure of the pipe or welds~ corrosion, electrolysis, traffic vibration,
earth tremors, nearby .blasting, washouts, land settlements, floods, erosion, mechanical
damage to the pipe, etc.
Since the sheer strength of steel is very much less than its bursting strength, there
is a great likelihood that even a slight rupture will tear into a long horizontal break at
the instant =o.f rupture. In one outstanding example at King of Prussia, Pennsylvania,
such a:~ea~:extended for so.me 3,150 feet until finally stopped by the construction at a
railroad underpass.. The thirty-inch pipe involved was ripped into ribbons, as though
by giant pinking shears, and spewed all over the right-of-way, with sizable pieces even
locgmg in the tops of trees..
In the case of a simple rupture, where ignition does. not occur, the hazard is
usually limited to the danger of being struck by the pipe, pipe fragments, rocks, or
other debris. In one instance, on the occasion of a break in Northern Connecticut, a
housewife described a veritable rain of rock and stones around her home, some 750
feet from the pipe line. Unsuccessful attempts have been made to require transmission
companies to exclude rocks and large stones from backfill; the companies being in opposition
because, among c,ther reasons, such heavy fil! he_lps to hold the pipe down in the
event of a rising water table..
After the initial blast damage, the obvious"danger of a rupture is the ever-present.
one of ignition. Since the Unitedi States Bureau-~-f- M~nes has determined that ignition
of a natural gas-air mixture occurs with static sparks of 2/10 of a millijoule, with this
being 1,000 times less energy than that liberated by-the combustion of the smalleit
particle of coal that can be weighed on a sensitive analytidal balance, it is safe to assume
that nearly all major high pressure pipeline rupture will be followed by fire. At least
this assumption should be used as a bagis .for the complete evacuation of the area of a
leak, and of keeping even. firemen and other emergency workers at a safe distance at
all times. Anyond whb has ever been singed by the puff of a gas oven that was a
little too full of gas-air mixtures when lighted, will know that "safe distance" does
not mean adjacent to the column of escaping gas. Moreover, in anticipating ignition
it is well to remember that a small stone striking the pipe or debris may be all that is
needed.
Under ordinary conditions existing i-n ho~es=xnd ih-industry, it is difficult to
insure the complete absence of such sources of ignition as, open flames, static sparks,
inductive sparks, electric arcs, hot wires, compression, shock, friction, heated surfaces,
and hot flying particles.
As distinguished from a rupture even though the same may be, and usually is,
followed by fire, an explosion consists of the actual chemical : combination of gas and
oxygen, usually under relatively close confinement. If a combustible gas is added continuousiy
to a given quantity of air the concer~trationof the gas increases and eventually
:’eaches a value known as the lower limit of flammability. Gas-air mixtures whose concentrations
are below the lower limit of flammability are not flammable. With further
~ontinued addition of combustible gas, a second value, known as the upper limit of
flammability, is reached. Gas-air mixtures whose cor~c~’~trktions, a-re- Xbove the upper
limit of flammability are not flammable. Mixtures whose concentrations~._lie:_-b_etNe_en