HAZARDS Low Pressure and Vacuum Systems

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HAZARDSLow Pressure and Vacuum Systems
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PRESSURE SAFETY
Can you get hurt with low pressure?
Lets review the details.
Force Pressure multiplied times Area
Its like many small weights sitting on a surface
which add up to a big weight.
So at a given pressure, the LARGER the area The
LARGER the force.
The next graphic is slow so give it a few seconds
after clicking
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EXAMPLE 1
Force pressure multiplied by area so
12 X 12 Square Door
10 psig
10 psi pressure on a 12x12 square surface area
(144 square inches) is 1,440 pounds of
force! Calculation 144 X 101,440 lbs of force.
This is equivalent to an object that weighs
1,400 lbs.
And you can bet the door weighs less than 1,400
lbs -- if suddenly released it goes flying.
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EXAMPLE 2
Force pressure multiplied by area so
24 X 24 Square Door
10 psig
10 psi pressure on a 24x24 square surface area
(576 square inches) is 5,760 pounds of force!
Calculation 576 X 10 5,760 This is equivalent
to an object that weighs 5,760 lbs.
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BE AWARE
Can you get hurt with low pressure?
ABSOLUTELY !
And be especially careful with large surfaces
like manways. 1/2 psi may not even register on
the gauge but its enough to send a hatch flying
if all the bolts are removed and the gasket is
stuck.
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Low Pressure Hazard

• This door had the equivalent of 1915 lbs of force
  on it. And at only 2.8 psi.
• The door only weighs about 15 pounds -- much less
  than the 1915 lbs of force on it. Therefore,
  when it came loose, it slammed open seriously
  injuring an operator.

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VACUUM SAFETY
Atmospheric Pressure

• The same concepts apply to vacuum
• However, in vacuum systems the pressure is
  pushing inward, not outward.
• The pressure comes from the atmosphere -- we
  dont feel it but a tank does when you pull
  vacuum on it.

Vacuum

• Atmospheric Pressure (at sea level) is about 14.7
  psi, therefore full vacuum is -14.7 psi.

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VACUUM SAFETY

• If a tank is not designed for vacuum, odds are it
  will be damaged if placed under vacuum.
• Low pressure storage tanks and railcars are
  particularly susceptible to damage.
• This is why those low pressure switches on the
  suctions of blowers are so important -- you
  cant manually shut the blower down fast enough
  to avoid damage if the blower pulls vacuum on a
  tank.
• Not only is the equipment damaged but the
  hydrocarbon contents may also be released.

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Covered Vent

• This tank collapsed while being pumped out!
  Painters had covered the vent with plastic
  sheeting. The steel tank collapsed before the
  plastic sucked through.

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Railcars

• No match for a closed vent while pumping out the
  car.
• Dont you figure the person standing here got a
  sinking feeling.

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Cant Happen Here!
Or Can It??
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Final Thoughts

• Never underestimate the potential of a low
  pressure or vacuum condition to cause damage.
• Be especially careful when working around or
  removing large manways or hatch covers.
• Make a final check just before the job begins to
  confirm that ALL the pressure is bled off -- it
  only takes one valve leaking through just a
  little.
• Leave a few bolts in (but loose) until the gasket
  seal is broken. If the system has a little
  pressure this will keep the manway from striking
  someone.
• It doesnt look like a big hazard -- but under
  the right conditions it can be!