Nitrogen Compressor Leak Survey
Nitrogen Compressor Leak Survey
(OP)
Hello,
I am looking to justify/reject a project to add some O2 analyzers in a room where we have some Nitrogen Compressors. I believe the worst case would be a leak from a flange. The PSV's on the compressor discharge outside, so this should not be an issue. I have source models from Crowl and Loveur's "Chemical Process Safety" Book to determine the N2 leak rate. Questions that arise are:
1. Should I assume the leak from a flange will be a full diameter leak? The book has source model on "leak from a hole". I was just going to assume the leak would be the full diameter and calculate it that way.
2. What do I need to look at to see if we need the O2 analyzers (room size, ventilation, proximity to doors and windows)? Anyone perform an analysis like this before? Should there be air turnover in the room of some ratio? Or does another "rule of thumb" exist?
Please give me a path to move forward to make this determination. Thanks.
I am looking to justify/reject a project to add some O2 analyzers in a room where we have some Nitrogen Compressors. I believe the worst case would be a leak from a flange. The PSV's on the compressor discharge outside, so this should not be an issue. I have source models from Crowl and Loveur's "Chemical Process Safety" Book to determine the N2 leak rate. Questions that arise are:
1. Should I assume the leak from a flange will be a full diameter leak? The book has source model on "leak from a hole". I was just going to assume the leak would be the full diameter and calculate it that way.
2. What do I need to look at to see if we need the O2 analyzers (room size, ventilation, proximity to doors and windows)? Anyone perform an analysis like this before? Should there be air turnover in the room of some ratio? Or does another "rule of thumb" exist?
Please give me a path to move forward to make this determination. Thanks.





RE: Nitrogen Compressor Leak Survey
RE: Nitrogen Compressor Leak Survey
I think you have a typo, 6 air changes per minute would be a huricane. At 6 air changes per hour I have a real hard time keeping processes from freezing this winter.
RJB32482,
Oxygen defeciency is a real problem in spaces where nitrogen is processed. It is a pretty common practice to either have whole-room oxygen detectors or have proceedures that require persons entering the space to have portable detectors. With regard to your leak size, API RP 500 has a proceedure for estimating leak potential from flanges and fittings (oddly enough called the "Fugitive Emissions Method") that has a factor for flages that is far smaller than a full-flange leak.
David
RE: Nitrogen Compressor Leak Survey
RE: Nitrogen Compressor Leak Survey
RJB32482:
This is not a direct answer to your question, but I think it is still useful to understand the seriousness of possible nitrogen leakage into a room or any other closed space.
In the book "Forensic Pathology", Second Edition, Vincent J. M. DiMaio and Dominick J. DiMaio, ISBN: 0-8493-0072-X, at page 231, it is stated that: At oxygen concentrations (in air) of 4 to 6%, there is loss of consciousness in 40 seconds and death within a few minutes”.
You can read that at htt
The cost of installing oxygen analyzers in the room is probably insignificant compared to the possible serious consequences not only of a flange leak but also of a catastrophic pipe failure for one reason or another. Ventilation systems can also fail.
Milton Beychok
(Visit me at www.air-dispersion.com)
.
RE: Nitrogen Compressor Leak Survey
I know someone that had a nitrogen exposure and quick response by the fellow workers lowering him into the tank saved his life by raising him back up. He just slumped over and went to sleep. It can happen that fast.
The oxygen analyzers we use here are less than $1500. They put out a 4-20 ma signal to the DCS. Calibration is required once a month. People are comfortable working around it. Contact your local MSA rep for more info.
RE: Nitrogen Compressor Leak Survey
What say you RJB32482?
RE: Nitrogen Compressor Leak Survey
So if I gave them the data that the room could fill with nitrogen in seconds or even minutes, that the O2 sensors would be justified. So that's why I asked about leak rates and ventilation.
Please reply if any other scenarios like this occurred in your plants and how you justified it to the other workers.
Thanks.
RE: Nitrogen Compressor Leak Survey
A 1" nipple breaking would make the building unsafe in minutes. I can't remember the rule of thumb now, is pressure psig * hole diameter inches = escape rate in MSCFD I believe.