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Permalink Reply by Nick Daly on May 11, 2011 at 12:34pm

H2S is big deal for me. I've been on a boat under a platform when a guy openned a valve and dumped it on us. I've crawled into compartments in a mat rig and barges full of the stuff.

 

There is an H2S field in the main pass south of the Mississippi River outlet where they are mining for sulfur. You can see there are 3-4 platforms with long bridges connecting them, as they mine, the platform sinks. These have boat landings at several levels above the water so when the platform sinks there is a new landing ready.

 

A lot of drilling rigs get H2S buildup in their underwater compartments  because these confined spaces never get openned or properly flushed. This is the main hazard for divers. H2S doesn't just float around in the water, it disperses, it is heavier than air so when they dump it from platforms it can be a big hazard for boats, anything on the waterline. It's a gas so it doesn't get into the water, it must be formed there in those confined spaces.

 

When we get into confined spaces, I can smell it first off. It turns brass black. My old 17 B's weights have all turned black (when you see a hat with black weights, you know he's been in some bad s***) and what we'd do is open a hatch, maybe leave my knife there with the brass clip hanging into the compartment. Come back the next day and see if it turned black, leaving the hatch open so the gas can come out. It helps to cycle water through the compartments if possible.

 

H2S is also in natural gas, however if you are in a pool of natural gas you have better things to worry about than H2S. It can be present in the swamps or stale bodies of water, I've never encountered it in any of my swamp diving however.

 

When we go to the H2S field everyone is fit tested, the boat is outfitted with SCBA's, and everyone has to take an H2S course and pass a test. When we get to the rig, we take a site safety walkthough of the rig, don't touch this valve, lock-out-tag out stuff. That particular job went great until the rig did its crew change. A guy came out, didn't see our boat under the platform and dumped the gas on us. Our sirens went off (luckily we were standing by and not in the water) people ran up to the SCBA's, we put them on and untied the boat and hauled ass. We could smell it so it wasn't fatal and at a low PPM. So that incident wasn't in the water and totally could have been avoided had the guy looked down.

 

For your questions, in 10 years of diving, I've encountered it on 5? jobs. Almost every time I get in a confined space underwater, I double check, ask a lot of questions; when was the last time this compartment was openned, can the compartment be flushed, please be ready to pull my dead ass out at any time.

 

Geographicly... that's a good question, there are many sulfer mines around the world I'm sure, underwater is a different story, as far as I know, the main pass has the only subsea mine. This page may help: http://http://en.wikipedia.org/wiki/Hydrogen_sulfide 

 

To minimize exposure the company should have contractors go through the H2S course, set up the boat or site with SCBA's and the alarm system. H2S deadens the senses, so if you smell it, it has a low PPM and you will not drop dead, yet. Ventilate Ventilate Ventilate!

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Permalink Reply by Mike Wolfe on May 11, 2011 at 10:06pm

 

Simon,

As you work for Analox, I'm sure you have much more knowledge at your disposal than anyone on this forum! As I'm sure you're aware, our first line of defense is the bellman to visually monitor the bell trunk and not permit it to be in a position where gas is bubbling in to the bell. I'm sure you're aware we have no real way to monitor for H2S in the bell, even though it is a potential hazard in many off-shore gas fields the world over. An in-bell monitoring device would help mitigate one potential hazard of oilfield diving. A device to monitor for the presence of hydrocarbons could prove useful, too. But, like most expensive diving gear, I wouldn’t expect either to be widely adopted until it is mandated by the OGP or local governing bodies (notice I didn't mention ADCI or IMCA). That means we probably will not be using them here, in the GOM, even if there is a good argument to have them.

Yes, I'm a cynic.

Pemex has plenty of sour gas in their offshore fields as well as the Louisiana GOM fields cited in the previous post.

While preparing for a sat job here in the GOM, a few years back, a major contractor felt hydrocarbons could possibly contaminate the bell atmosphere, as we would be working near a sizable gas leak. They sent to us, on the job, Drager tubes to check for hydrocarbons in the bell atmosphere. We were curious as how to read the measurement at depth to achieve the correct ppm and contacted Drager. Drager immediately responded, saying to not use the tubes in a hyperbaric environment as they give off noxious fumes! Nobody in management had bothered to contact Drager before sending the tubes out on the job!!!

Luckily, the project was abandoned before any diving took place. 

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Permalink Reply by Mike Wolfe on May 11, 2011 at 10:25pm

 

That fine blend of complacency and incompetence. This industry has a habit of attracting people that “Know” everything about everything.

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Permalink Reply by Simon Lunt on May 12, 2011 at 12:57am

Hi Mike,

 

I'm grateful for all of this excellent information and feedback.

 

Analox do actually manufacture a hyperbaric hydrocarbon monitor details of which can be found at this link on our website: Analox Hypergas MkII.  The unit is named in the OGP 411 Report as a requirement in the diving bell.  It is also mandated by BP, Shell & Total.  Hydrocarbon monitoring is also included in the revision to ABS's guidelines from 2012 and is being considered by IMCA to be included in their D24 saturation system doc**ent.

Our ideal plan is to incorporate the H2S sensor (and display) into the Hypergas.  I hope to deliver a paper on the issue at the new CDDO conference in Singapore next April.  We delivered a paper at IMCA in Dubai which proved popular but when we delivered the same paper at UI earlier in the year hardly anyone turned up!

 

There is another issue with using Draeger tubes for sampling hydrocarbons in that they are not able to cope with the complexity of the mix.  We have an independent report (from Unimed Scientific) which states this.

 

Thanks again for the comments.  I should have used this forum ages ago!

Simon

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Permalink Reply by Mike Wolfe on May 12, 2011 at 11:25pm

Thank you Simon, I had not seen the Hypergas before. I guess I should be reading Longstreath's forum.

 

Simon wrote:

"We delivered a paper at IMCA in Dubai which proved popular but when we delivered the same paper at UI earlier in the year hardly anyone turned up!"

 

Thank you for reinforcing my cynicism.

 

An all- in-one solution would be best, in my mind, as the contractors would only have to buy one piece of gear that OGP could mandate for every bell. Then the diver would have the equipment when he needed it, and not have to hear: "Oh, the H2S analyzer is on the next crew boat coming out. Just move the bell, if you see bubbles."

  

@ Derek, thanks for the link!

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Permalink Reply by Derek Moore on May 12, 2011 at 12:22pm

Hi Simon,

Currently in the NS most companies use the Hypergas units following the Stolt incident some years ago and have no issues with the current models.

As for H2S we are currently trailing the Crowcon Gasman Alarms in the bells and they seem to work fine. http://www.crowcon.com/pages/products-amp-services/personal-amp-por...

Contact Subsea7 for feedback.

To answer your questions

1) How often does H2S affect your operations? Only in H2S producing fields.

2) Where is H2S most prevalent geographically? Varies in the North Sea. Brent has issues.

3) What precautions do you currently take to minimise your exposure to H2S? Fit monitors on deck and in the bells as well as training and information to the guys

 

 

 

Derek Moore

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