Week 5 Pressure Safety
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Transcript of Week 5 Pressure Safety
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HAZARDSLow Pressure and Vacuum Systems
HSE TrainingPrepared: March 2002
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PRESSURE SAFETY
Can you get hurt with low pressure?
Force = Pressure multiplied times Area
Lets review the details.
Its like many smallweights sitting on a
surface.
AND many small weightsadd 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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Force = pressure multiplied by area so:
EXAMPLE # 1
10 psi pressure on a 12x12 square surface area (144 squareinches) is 1,440 pounds of force!
Calculation: 144 X 10=1,440 lbs of force.This is equivalent to an object that weighs 1,400 lbs.
12 X 12 Square Door
10 psig
1,440 Pounds of Force
And you can bet the door weighs less than 1,400 lbs -- if suddenly released it goes flying.
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10 psi pressure on a 24x24 square surface area (576 squareinches) is 5,760 pounds of force!
Calculation: 576 X 10= 5,760This is equivalent to an object that weighs 5,760 lbs.
24 X 24 Square Door
10 psig
5,760 Pounds of Force
Force = pressure multiplied by area so:
EXAMPLE # 2
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3,140 Pounds of Force
20 in. Manway
10 psi pressure on a 20 manway (314 square inch surface area) is3,140 pounds of force!
Calculation: 314 X 10= 3,140This is equivalent to an object that weighs 3,140 lbs.
And a 20 manway only weighs about 275 lbs.
Force = pressure multiplied by area so:
EXAMPLE # 3
10 psig
Again -- if suddenly released it goes flying.
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Can you get hurt with low pressure?
ABSOLUTELY !
BE AWARE
And be especially careful with large surfaceslike manways. 1/2 psi may not even register on
the gauge but its enough to send a hatchflying if all the bolts are removed and thegasket is stuck.
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Low Pressure Hazard
This door had theequivalent of 1915 lbsof force on it. And atonly 2.8 psi.
The door only weighsabout 15 pounds --much less than the1915 lbs of force on it.Therefore, when itcame loose, it slammedopen seriously injuringone of our coworkers.
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VACUUM SAFETY
The same conceptsapply to vacuum However, in vacuum
systems the pressure is
pushing inward , notoutward. The pressure comes
from the atmosphere --we dont feel it but atank does when you pullvacuum on it.
Vacuum
Atmospheric Pressure
Atmospheric Pressure (at sea level) is about 14.7 psi,therefore full vacuum is -14.7 psi.
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Covered Vent
This tank collapsed while being pumped out!Painters had covered the vent with plasticsheeting. The steel tank collapsed before theplastic sucked through.
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Railcars
No match for a closed vent while pumping outthe car.
Dont you figure the person standing here gota sinking feeling.
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Cant Happen Here!
Or Can It??
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Final Thoughts
Never underestimate the potential of a lowpressure or vacuum condition to causedamage.
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 fromstriking someone.
It doesnt look like a big hazard -- but under the right conditions it can be!