HAZARDS Low Pressure and Vacuum Systems

1. HAZARDSLow Pressure and Vacuum Systems HSE Training Prepared: March 2002

2. PRESSURE SAFETY Can you get hurt with low pressure? Lets review the details. Force = Pressure multiplied times Area It’s like many small weights sitting on a surface. AND many small weights 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

3. 1,440 Pounds of Force EXAMPLE # 1 Force = pressure multiplied by area so: 12” X 12” Square Door 10 psig 10 psi pressure on a 12”x12” square surface area (144 square inches) 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. And you can bet the door weighs less than 1,400 lbs -- if suddenly released it goes flying.

4. 5,760 Pounds of Force EXAMPLE # 2 Force = pressure multiplied by area so: 24” X 24” Square Door 10 psig 10 psi pressure on a 24”x24” 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.

5. 10 psig 3,140 Pounds of Force EXAMPLE # 3 Force = pressure multiplied by area so: 20 in. Manway 10 psi pressure on a 20” manway (314 square inch surface area) is 3,140 pounds of force! Calculation: 314 X 10= 3,140 This is equivalent to an object that weighs 3,140 lbs. And a 20” manway only weighs about 275 lbs. Again -- if suddenly released it goes flying.

6. 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 it’s enough to send a hatch flying if all the bolts are removed and the gasket is stuck.

7. 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 one of our coworkers.

8. 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 don’t 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.

9. 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 can’t 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.

10. 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.

11. Railcars • No match for a closed vent while pumping out the car. • Don’t you figure the person standing here got a sinking feeling.

12. Can’t Happen Here! Or Can It??

13. 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 doesn’t look like a big hazard -- but under the right conditions it can be!