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# Dispersion modeling and locating a rupture disk tail pipe exit

## Dispersion modeling and locating a rupture disk tail pipe exit

(OP)
I have a new 10" rupture disk tail pipe to route, and specified it must be above the nearest building eve by 10 feet, and if an eve was within 20 ft, I requested the line be routed up past that higher roof eve on the "penthouse". I did it to maximize dispersion, for high velocity outflows and keep slow residual fumes from coming back down to grade between the buildings. I am receiving a lot of pushback, as if this is not needed and should only be justified by dispersion modeling.

It was my understanding that typical dispersion modeling was not intended to determine if such a penthouse could be ignored. fyi -- The penthouse is 40'W x40'D x 15'H and flush to the long wall on a 200' x 150' x 25' gable roof warehouse. Parallel to this wall about 50 ft away is a control room, some tanks, pipe rack and at the end of the wall, a smoke shack, so people go back and forth along this wall.

I realize I need a dispersion model to know where health effects, can reach, but is it meant to handle the situation described?

### RE: Dispersion modeling and locating a rupture disk tail pipe exit

Doubling the height is likely to have more than a squared effect support design parameters, probably making your 20ft height impossible to design using the current diameter. You should be sure you need 20ft before specifying that height. Did you do any dispersion modelling at 10ft to prove that you do need it?

### RE: Dispersion modeling and locating a rupture disk tail pipe exit

Any fixed distance / height rules are likely to be quite conservative as it has to look at the worst case.

It is a little difficult to work out your description and a sketch would be of more use, but dispersion modelling of different flows would seem to be required to show the impact at different flows, wind conditions temperatures etc.

Also depends on what it is you're potentially venting.

As for people, you can probably assume that if the BD goes off they will run away quite rapidly, so the low flow case may only need to consider entry into buildings.

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