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# Safe working distance

## Safe working distance

(OP)
Dear Tank Builder,

Dome roof tank 31 M dia x 14 M Ht designed as per Annex F with 0.75 psi design pressure.

As required by appendix F, the tank must be air tested at 1.25 x 0.75 psi.

The question is : is there any rule of thumb or engineering calculation about safe working distance during the air test.

We are using a pressure gauge and water manometer. How far we are shall or should be from the tank during the air test is in progress.

Thanks.

Syah

### RE: Safe working distance

ASME PCC-2 Article 5.1 Appendix II and III could provide guidance. Appendix II calculates the stored energy based on volume and pressure. Appendix III then calculates the safe distance based on this stored energy. This distance is based on blast wave damage to employee's ears. It also provides a table of fragment throw distances so you can judge if employees should be behind solid barricades.

PCC-2 may be written for pressure vessels with much larger pressures, but I would think the distances should still be a reasonable estimate if you have nothing better.

### RE: Safe working distance

Well I wouldn't stand on top of it.

I think you have two issues

Potential flying off of a large item ( say a manhole)

Tearing / rupturing of the tank or roof

So stay out of line by say 10m of any item which could be ejected.

Erect a shelter ( scaffold tubes would do) within 5m of the tank to do the monitoring etc

Keep everyone else back at least 15m in case the tank shell falls over.

1psi isn't a lot of pressure but you have a lot of sqin so a lot of force.

However if you get a significant failure it should vent quickly.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Safe working distance

That's a famous one alright, but I think it was a bit more than 1 psi....

The adjacent pipework was being air tested and wasn't isolated properly from the tank.

This is a bit different.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Safe working distance

When you talk about "air testing" of your large tank, you don't mean pneumatically testing the entire tank, do you ?

Aspects of pneumatic testing of a flat-bottomed tank is discussed here:

API-650; F.4.4 When the entire tank is completed, it shall be filled with water to the top angle or the design liquid level, and the design internal air pressure shall be applied to the enclosed space above the water level and held for 15 minutes. The air pressure shall then be reduced to one-half the design pressure, and all welded joints above the liquid level shall be checked for leaks by means of a soap film, linseed oil, or another suitable material. Tank vents shall be tested during or after this test.

Interestingly the test involves filling the tank with water then pneumatically testing the top space, presummedly, to reduce stored energy...

Do you have a tank fabricator/ construction firm that has EVER only pneumatically tested a tank this big ?

If you cannot find a fabricator/ construction firm that has EVER done this before/ then you have your answer ...

MJCronin
Sr. Process Engineer

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