pressure safety

8/3/2019 Pressure Safety

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HAZARDS

Low Pressure and Vacuum Systems


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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 small weights

sitting on a surface whichadd 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 square inches) is1,440 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 Door10psig

1,440 Pounds of Force

And you can bet the door weighs less than 1,400 lbs -- if suddenlyreleased it goes flying.


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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.

24 X 24 Square Door

10 psig

5,760 Pounds of Force

Force = pressure multiplied by area so:

EXAMPLE # 2


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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 it

came loose, it slammedopen seriously injuringan operator.


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VACUUM SAFETY

The same conceptsapply to vacuum

However, in vacuumsystems the pressure is

pushing inward, notoutward.

The pressure comesfrom the atmosphere --we dont feel it but a

tank 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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VACUUM SAFETY

If a tank is not designed for vacuum, odds areit will be damaged if placed under vacuum.

Low pressure storage tanks and railcars areparticularly susceptible to damage.

This is why those low pressure switches onthe suctions of blowers are so important --you cant manually shut the blower down fast

enough to avoid damage if the blower pullsvacuum on a tank.

Not only is the equipment damaged but thehydrocarbon contents may also be released.


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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 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 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 throughjust 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 underthe right conditions it can be!

pressure safety

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