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Posted By Uday
Iam confused and not sure which is right and which is wrong.
Iam being advised that when the H2S level is inbetween 01 ppm - & - 30 ppm ........Ventilate work site....NO work with flame....Work may proceed.....continuous monitoring required....check display regularly that the readings are stable or reducing until 0 ppm is achieved..
5ppm - 10 ppm work may proceed on Team leaders instructions...
10 ppm - 15 ppm....Ventilate work area....
above 15 ppm...DO NOT VENTILATE,barricade area,direct public & staff away from site....
This is comming from one of our MAJOR reputed clients ....
May I request the readers of this forum to advise me that the clients are 100% incorrect and any suggestions that you may have....SAFETY OF HUMAN LIVES is of prime importance in this organisation so they say....and never leaves an opportunity to hammar contractors for violation of safety rules and regulations....
Regards and thanks....
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Posted By Chris Lloyd
Uday
From memory the figures sound correct, and I would say your client is 100% correct.
H2S is extremely dangerous and can kill at low concentrations in the atmosphere ( 1000ppm which is 0.00001%). If you search the internet there are many sites with information on H2S.
Your client who, I am assuming, owns the location where you are working has these rules in place to protect employees, contractors and the general public. Not to bash the contractors.
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Posted By Neil Pearson
I agree. My copy of EH40 has gone walkabout again so I can't check the safe limits, but from memory hydrogen sulphide is even more toxic than hydrogen cyanide, and will be fatal above certain levels. Also, the sense of smell doesn't help - above a certain concentration you stop smelling the stuff, but you may think you're safe because you can't smell it. Don't assume the client's just being awkward.
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Posted By peter gotch
Uday
In the UK the occupational exposure standards for H2S are
5ppm - 8 hour time weighted average (TWA)
10ppm - short term exposure limit - 15 minute TWA excursion value.
Regards, Peter
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Posted By Liam Nolan
Hi,
H2S is extremly dangerous as you already know.
The TWA is 10ppm and STEL is 15ppm
The gas is extremly flammable and likly to explode LEL is 4% with the UEL 44%.
Our gas monitors on sites and locations with H2S is 5ppm displays an amber warning. Once it hits 10ppm its immediate evacuation utilising escape BA (as specified in our RA they have to be carried).
Risk phrases on some information I have shows
R12, R26 & R50.
We make no allowances for the STEL as our gs monitors are set to 10ppm.
The thing with the monitors is that on non-portable ones you don't know what the ppm is - so you evacuate.
Even if the portable ones do read beyond 10ppm we still demand evac.
I will email the MSDS sheet I have for this substance. If you want to ask me about any part of it I will try and answer your question.
Liam
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Posted By Nicholas Ross-Clunis
Concenttation: Less than 1ppm Detectable by smell; 10 ppm TLV Long Term Exposure Limit(8 hour average value) ACGIH; 15 ppm Short Term Exposure Limit (10 min average value); 30ppm Eye and respiratory tract irritation; about 100 ppm Loss of sense of smell; about 500ppm Dizziness, Headache, Nausea, Abdominal pains within 15 minutes, loss of conscience and possible death after 30 minutes exposure if effective resuscitation is not applied;
1000ppm Rapid unconsciousness followed by death within minutes.
There is no EU IOELV as yet
Explosive range 4.5-45.5% vol in air
Further problems with H2S is the possible formation of Pyrophoric Iron.
Regards,
Nicholas
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Posted By Stuart Nagle
What should also be remembered gents is that gas (including H2S) can build-up in the body. Hence the 8 hour Time Weighted Average (TWA) is being very low at 5ppm.
This is for work that is taken over an 8 hour shift, ergo the maximum exposure to H2S in 8 hours is 5ppm. When a gas monitor is set to an 8 hour TWA it will alarm if the ppm going through the monitor at any time during the 8 hour shift go above 5ppm level. This equates to you breathing in the 5ppm!!
Also remember that readings taken before entry into areas where sludge/detritis may be present may provide a false sence of security, as H2S is mainly generated by the anaerobic action of micro-organisms (organisms that live without oxygen and create H2S as a bi-product) and gas can build up in pockets in the sludge/detritis (like an aero chocolate bar), and be released into the atmosphere when persons tread in the sludge/detritis present.
The other alarm settings for H2S on gas minitors - principally for confined spaces use - are:
15ppm for short term working - averaged over 15 minute periods and as mentioned in the thread above, and
50ppm where a gas monitor will alarm instantaneously - so as to account for the often very quick rise in H2S through either persons causing it to arise, as above, or the gaseous elements drifting along (e.g. through sewers due to air flow) or the sudden releases of gas H2S bubbles from sludge/detritis where they have become too large to be retained in the sludge/detritis matrix.
H2S is a killer and can quickly overpower persons exposed. It is not detectable by sight or smell at concentrations that are harmfull.
I have been involved in works in sewers, treatment works and pumping stations and sewerage plant most of my working life and I can honestly state that I have not had a 'smell' of H2S (often reported to smell like rotten eggs)- probably because my exposure was over and above the point where H2S anaesthetised my sense of smell - if you don't belive me ask a sewerman if sewers smell when they are down there - they will tell you (if not winding you up) that they don't - because it is likely their sense of smell is being effected by tiny amounts of H2S... On the other hand, if you stand over an open sewer....ppphhhoouuurrrrrr...
In high concentrations H2S is not only toxic, it is explosive, and an ignition source from non-intinsically safe equipment, tools, flame/sparks etc can either cause a flashover or an explosion (depending on the concentrations of oxygen present).
So be carefull. Follow the clients instructions and the very necessary safe systems of work - including pre-entry monitoring and continuous monitoring throughout the work.
If work involves using potential ignition sources, the processes of ventilation, inert gas purging and forced air ventilation may be necessary to ensure the atmosphere remains safe.
I suggest you take a good look at the Confined Spaces Regulations 1997 which also includes cleansing of areas where residues (such as sludge and detritis remain in a space) prior to entry being permitted.
The golden rule being at all times, that if the work can 'reasonably practicably' be carried out without entry, then entry is NOT to be permitted.
Stuart
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Posted By Uday
Hello All,
Thanks for your replies.......So this means that we STOP all work and evacuate if the monitor reading shows....10 ppm and above ...is that right please ?
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Posted By Liam Nolan
Hi,
Yes evacuate once you get a 10ppm alarm.
Escape BA should also be specified if you are working in areas that may prevent a quick retreat from the source. (It would possible be easier to say that Escape BA should be carried at all times unless your RA dictates full BA or you are not entering the danger area - i.e. standing over the ope in the sump which means 'two steps away from it you will be in the clear' (figure of speech to illistrate my point, two step may not be enough).
Then again if you are standing over an open sump and looking in you could get a shot of H2S and fall in to the sump - other controls need implementing to eliminate this - your RA is going to be very important.
Again, our alarms sound a 5ppm (I also am in the Waste Water Treatment sector) and we require evac at this stage. mainly because if the gas level is rising you don't know if it is going to stop at 5,6,7 ppm etc. it can get to 10ppm very very quickly.
The exception being that the operators are wearing full BA. Of course if they are wearing BA then you will most likely be working under a Confined Spaces Permit which will dictate the entry, exit, working, and emergency extraction requirments.
This is not a small area, be fully satisfied that your controls for the hazards involved are comprehensive.
Regards,
Liam
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Posted By Stuart Nagle
Hi, Uday.
If you are using a gas monitor designed for confined spaces use, and the monitor is set to operate on the 8 hour TWA setting, it will automatically alarm at any time during the 8 hour period if exposure, as recorded by the monitor, goes above 5ppm.
If set to monitor for short duration works it will alarm at the appropriate level for short duration works, as mentioned above.
Your client appears to be saying;
1) You must monitor the atmosphere to ensure it is safe to work (before work and continuously whilst works are ongoing)
2) If the percentage of H2S is below 5ppm thats fine - but moiitor continuously to ensure it remains this way
3) If the H2S in the atmosphere is above this level (but less than 15ppm) you can still work provided the space is ventilated prior to works proceeding to ensure that the H2S in the space is evacuated from the space so conditions are normalised (or drop below and remain below the minimum acceptable level)
4) If the H2S rises above 15ppm then the space MUST be evacuated immediately (and do NOT ventilate the space - as introducing oxygen into the space may create an explosive mixture in the atmosphere that an ignition source could ignite)
Your client is correct. Use of appropriate monitors and following the requirements of the Confined Spaes Regulations 1997 (as mentione in the thread above) should ensure a safe place of work and safe systems of work are employed.
Hope this answers your question.#
Stuart
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Posted By Paul Bagley
I work on a petro chemical water treatment plant and come in to daily contact with H2S reading from 5ppm to around 30ppm. Could anyone give me any information concerning the possible long term health effects this daily contact may have.
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