Measure or Test Methane in Non-confined Space

It might be hard to make a meaningful standard for gas accumulations in open air, if only from the difficulty of getting consistent readings. However, nothing prohibits extra efforts toward safety. In your example, it could make sense to soap-test (or electronically sniff) joints and seams that might possibly have leaks.

Soap testing makes sense, especially when the joints are few and easy accessed, as it is in my case. So, question is within what radius should the joints be tested?

I am involved with test natural gas components which are tested for the automotive industry 24/7 in a special covered outdoor room . It is designed to safely readily relieve pressure should there be unintended leak and ignition "event". But the primary protection is provided by methane detectors that trip a full system shut down (CNG feed is stopped and electrical systems cease) at 5% of the LEL (lower explosive limit) for fuel/air ratio. This is essentially at 0.25% methane by volume. (For reference, methane air mixes burn well between 5% and 15% by volume). As far as I know, there are no exposure limits directly related to methane by itself as it is generally not considered to have any known negative health effects other than asphyxiation at extremely high concentration levels or fire risk as stated above. Not sure if that is relevant.

Thanks for the reply awelch. I am trying to understand how the special covered outdoor room is built. Is it only a roof, or does it have wall/walls as well? What are the room dimensions?

Are the detectors located near a restriction surface, ( near the roof, or near the corner of the roof with side-walls) ? I guess the detectors are not installed in the middle of open air space. Because that is my case.

The room (4 meter wide x 6 meter deep x 4 meter tall) uses concrete block and steel materials for construction for fire safety. The 3 back walls are concrete block and the 4th wall is essentially open with a swinging chain link entry door. The roof is corrugated steel.

An important design feaure is that the roof is designed to freely vent methane at the peak and along the edges where it sits 20 cm above the walls on posts. Multiple detectors are installed in the roof, near the roof / wall vent points and halfway up the walls at about 2 meters just above equipment. These points are the natural positions for natural gas to build up in the event of a slow leaks or sudden leak should a part under test fail.

It has been in operation for perhaps 10+ years (24/7).

I hope that is clear.

Maybe there's no standard because none is needed. You might find this NIOSH paper useful. It describes three conditions, a confined space, a totally open space, and an outdoor space with obstacles such as process vessels, piping etc.

It states that unconfined air-methane mixtures would require 22kg of high explosives to detonate the resulting cloud.

Personally I find this counter-intuitive, but I guess methane diffuses so fast in open air that the LEL (Lower Explosive Limit) for an explosive mixture can't develop. This seems to be borne out by this piece about LNG:

"...Is LNG flammable?

When cold LNG comes in contact with warmer air, it becomes a visible vapor cloud. As it continues to get warmer, the vapor cloud becomes lighter than air and rises. When LNG vapor mixes with air it is only flammable if it's within 5%-15% natural gas in air. If it's less than five percent natural gas in air, there is not enough natural gas in the air to burn. If it's more than 15 percent natural gas in air, there is too much gas in the air and not enough oxygen for it to burn..."

NB- This is not my field of expertise but I've worked around enough flammable gases like methane and hydrogen in power plants to know that if I can smell, feel, or hear it leaking then I better get out of there really, really fast.

This is a great topic. Thanks fro brining it up. I refer to the methane emissions in coal mines and the that encountered during methane extraction from lakes. There are only 3 of these lakes and all in Africa. The volumes of these emissions can be considerable.

The mines I refer to are in China where there are numerous fatalities each year. There standard methods of detection for mines.

In the methane extraction from lakes field there is a small, intimate click of professionals from mixed fields that have expertise in this area. They would also be interested in this topic. In addition, there is also the field of methane hydrates - situated in the ocean or in ice environments.

I would be interested in coming across cheap simple hand held devices for the purpose of methane detection. If anyone knows of such-like, please do enlighten us. By now, there must be a modern version of the 'canary in a cage' device.

The Health And Safety At Work Act 1974 covers this in the UK. There should be Permit To Work systems in place. There should be Hot Work Permit systems in place. There should be Confined Space Permit To Work systems in place. The authorised individual signing those forms, thereby warranting the health and safety of those carrying out the work and providing evidence that could be used at any subsequent inquiry proceedings in the event of an incident, will need to have demonstrated that all reasonably practicable steps have been taken to protect the individuals doing the job, including forced ventilation and personal gas monitoring equipment should the need arise.

Any leak of flammable gases represents a serious process materials containment issue, which needs to be addressed as a priority on both safety and economics of operations grounds, with safety being the driver.

If an operative is being asked to work in a space where the presence of a flammable gas/air mixture is a normal occurrence without appropriate precautions having been taken beforehand, then the Health and Safety Commission can begin proceedings for prosecution.