Safety (Ventillation) : TIG in confined space

[LambdaX]

Hi all,

First post.

My question is about TIG welding stainless in a confined space. I'm unfamiliar with atmospheric control.

Wondering if anyone can point me in the direction of a course / what is the training attended in industry for best practice, so I might make an informed judgement on how to go about this and quantify the risks.

My largest concern is asphyxiation, where argon displaces oxygen at the bottom of the container.

For context: Im investigating building a stainless steel water tank in the bow of a vessel (sealed space (with one opening).

Other practical solutions are excluded - being unable to fabricate elsewhere and install.

My intuition would suggest extraction and supply, one hose at the bottom of the space to remove argon at some specified flow rate E and air intake at the top of the space at a rate S such that S > E to create a positive pressure within the space. I am open to be corrected (please).

I am speaking from a place of complete ignorance and would appreciate a full criticism / risk factors I haven't acknowledged.

Feel largely in the dark and would love some theory + advice to latch on to, to get me going - seems an interesting subject, regardless.

 

[voipio]

How big is the tank, what is its shape, and how enclosed a space is it going to be? Is this being done commercially, or for your own hobby? The worst case would be if the top of the tank is being welded, with you inside the tank. It would be better to weld the top of the tank from the outside. Typical argon flow rates for TIG welding are in the region of 7 litres/minute. A relatively small duct, with its opening at the bottom of the tank, with an extraction fan on the end of it, should be ample to stop argon accumulating to any significant extent. An alternative might be to use an air fed helmet. Also, be mindful of the slightest shortness of breath, though this can be easily be caused just by holding your breath during the weld, which is something I find I do whilst running welds. In a commercial environment, an available oxygen level monitor might need to be specified in any risk assessment.

 

[indykid]

Do you have a budgie?

ETA - Levity aside, it's a very reasonable question. How much welding do you need to complete? Are you intending to weld all the seams from the inside? Can you partially fabricate outside and do the last welds in position?

A bathroom extractor type fan and duct would likely be more than sufficient and wouldn't move so much air as to be concerned about it disturbing shielding gas like an unducted fan.

 

[Munkul]

I used to plan and manage a lot of this kind of work. We had extraction from the bottom, as a minimum, sometimes also fresh air fed in. Key to these activities was risk assess against the specified hazards, and have a robust escape plan.
Google the HSE confined space guidance. It's quite helpful.
Ideally (and legally) you should complete some formal training before planning any confined space work. It's mostly common sense, but some stuff you don't know what you don't know...

 

[chrismac]

I used to plan and manage a lot of this kind of work. We had extraction from the bottom, as a minimum, sometimes also fresh air fed in. Key to these activities was risk assess against the specified hazards, and have a robust escape plan.
Google the HSE confined space guidance. It's quite helpful.
Ideally (and legally) you should complete some formal training before planning any confined space work. It's mostly common sense, but some stuff you don't know what you don't know...

would you also have had an emergency / rescue / recovery plan either in place or set up at the work site, I have been in confined spaces where you are attached to the tripod via a harness for the duration of the work, as you say all this becomes clear once you have the training you can appreciate the level of work that goes into the planning and risk assessments.

 

[Erie Fred]

would you also have had an emergency / rescue / recovery plan either in place or set up at the work site, I have been in confined spaces where you are attached to the tripod via a harness for the duration of the work, as you say all this becomes clear once you have the training you can appreciate the level of work that goes into the planning and risk assessments.

I just had my confined space refresher a few weeks ago....
It sounds like we are not that different in the rules department.

we have the tripods and harness, outside person must monitor, using a 4 gas monitor with hose leading
down to the bottom (and for certain area's, a check higher up in the tank as well)

 

[Munkul]

would you also have had an emergency / rescue / recovery plan either in place or set up at the work site, I have been in confined spaces where you are attached to the tripod via a harness for the duration of the work, as you say all this becomes clear once you have the training you can appreciate the level of work that goes into the planning and risk assessments.

always a standby man and a rescue plan, its a legal requirement, also I like to be able to sleep at night not having killed someone.

Sometimes the rescue winches aren't the right option, sometimes the plan was actually having a standby man with SCBA to assist with a rescue.
Sometimes when it was a flat bottomed open tank with specified risks reduced to practically zero, it was just having a standby person outside and a harness on the entrant with no line.
Gas monitoring was done on every entry because we already had the kit; but in some cases you can justify not having it if you have great ventilation.

 

[Morris]

I was also confined space trained and munkul, chrismac and eriefred have said it all.