3 replies to this topic

[ShaunHill]

We often use nitrogen for purging in the industry, but people seem to often ignore the hazards of working in an atmosphere that may have high levels of nitrogen.

The following link is an example of what has happened when people don't take this threat seriously:
www.csb.gov/completed_investigations/ docs/CSB_UnionCarbideFINAL.pdf

In particular, I think it should be noted that a person exposed to an atmosphere of less than 5% oxygen can go into a coma in 40 seconds.
This person will need some form of artificial resperation to have a chance of survival. Even if they are removed to fresh air, they may not start breathing on their own.

This is usually addressed for people doing vessel entry, but it can also be a threat for someone working near a vent point while purging is going on, or welders cutting into pipe that has had a nitrogren purge on it.

[Art Montemayor]

All:

I find myself compelled to add additional information and experience to this very, very important thread. But before proceeding, I want to personally thank ShaunHill for his professionalism and his engineering foresight in bringing this grave and serious subject to our attention. Whether you are a Student, a graduate engineer, or a registered professional engineer it is of vital importance to be aware of and learn by the tragic mistakes of others. I have always maintained that we engineers are held to higher standards and expectations by society. It is our legal and moral obligation to respond accordingly – especially when the stakes involve human lives. I can conjure no greater living Hell or mental torture for an engineer than the possibility of having to live knowing that he/she is responsible for the death(s) of fellow humans through a stupid mistake, oversight, failure to apply judicious measures, or mental laziness. Nitrogen Asphyxiation is such a case and the awful and tragic results that history shows us should be heeded and every step taken to avoid all such preventable occurrences.

The Union Carbide Corp. Nitrogen Asphyxiation Incident at Hahnville, Louisiana in March 27, 1998 is such an incident – and it could have easily been prevented. I believe Shaun’s URL has a flaw and the following got me directly to the website he quotes:

http://www.csb.gov/i...e=info&INV_ID=5

In the aftermath of the March 1998 Nitrogen asphyxiation incident at Union Carbide in Hahnville, LA, the U.S. Chemical Safety Board initiated a review of similar incidents nationwide. The CSB study identified a total of 85 incidents that occurred in the U.S. between 1992 and 2002 and involved exposure to a nitrogen-enriched atmosphere. Together these incidents caused 80 deaths and 50 injuries. The CSB developed a safety bulletin on nitrogen asphyxiation hazards, highlighting a variety of good practices aimed at avoiding such incidents. I highly urge each and every engineer who reads this thread to download, study, and avidly apply each and every recommendation issued in this bulletin. It can be downloaded at:

http://www.csb.gov/i...=info&INV_ID=41

In fact, I strongly advise all engineers – especially aspiring students – to go to:

http://www.csb.gov/i...ions&page=index

and download all the Adobe documents on the CSB completed investigations. Reading, studying, and learning by finding out what others did wrong – or didn’t do – is a superior and practical way of gaining valuable engineering know-how and experience. This is about real life – not theory.

In a recent thread on the Industrial Forum I shared a “near-miss” experience I had with Nitrogen Asphyxiation while managing a grass-roots plant startup in Belgium. But prior to that, in 1962, I had another N2 experience that left a scar in my career. I was managing a complex of industrial gas plants in Jamaica. One of the units was an air separation plant that operated 24-hr a day. During one holiday, while on the night shift (& without my knowledge), a local SCUBA diving enthusiast approached one of my operators and asked him to refill his SCUBA tank. We normally did this routinely, using a designed air manifold downstream of the dryers and upstream of the air separator columns. Since the plant was producing Oxygen into cylinders during that shift, my operator could not switch over to fill only one air cylinder. The customer insisted and requested that the operator employ a column side stream valve to obtain the HP air, insisting that he would pay extra for the service and wouldn’t cause any trouble. The operator relented, just to get the customer, out of his hair and did as he was requested. The customer went to his reef for a dive and never surfaced alive. His tank had been filled with a Nitrogen-rich mixture and he asphyxiated underwater. My operator was exonerated, but we all felt the sting and anguish of such a stupid and preventable accident or mental error.

As engineers, we are respected and acknowledged to be superior in our organized knowledge base and our logical thinking by society. With that recognition we also inherit a responsibility to that same society. Although we are not cerebral diaper-changers or mental baby-sitters for the rest of society, we stand to cause a lot of potential harm if we don’t do our job intelligently and diligently. We owe it to our society for the position we are given. No one else can do it but us.

Art Montemayor
Spring, TX

[avsp]

Shaun / Art,

Honestly, I used to treat nitrogen purging as one of the mundane activities of any project I was involved in!!!.......even during the HAZOP it was treated with as one of those "sundries" by just quickly looking into the basic system and checking the capacities for blanketing and ensuring relief valves is in place at an appropriate location and that was just about it!!!!!.........but reading your article and following the links that you all have suggested, I think I am grossly wrong!!!!!!!!!!!!!!!!..................I have started looking at Nitrogen systems / purging and related safety aspects in a new angle and more seriously.....I thank you all for bringing up this topic.

Art,

I always look forward to reading your responses on this forum on whatever may be the topic as I find them to be very insightful and informative.