Hydrogen Sulphide (H2S, sour or sewer gas) is very nasty stuff! It is invisible and heavier than air - and deadly. Whilst smelling like rotten eggs at low concentrations, at higher strengths it inhibits the sense of smell - making it undetectable to humans.
H2S occurs naturally when organic material decomposes in the absence of air. Amongst other places it is most often found in swamps, pits, tunnels, confined spaces, manure lagoons and perhaps most importantly in natural gas and crude petroleum deposits.
The presence of Hydrogen Sulphide in oil exploration and drilling, tar sands upgraders, refineries, natural gas facilities and pipelines makes it a constant threat to workers. Canadian Provincial and Federal regulations specify what level of exposure is permitted before protective equipment and procedures are required by workers.
H2S Exposure Limits
The levels of allowable exposure by unprotected workers were set in accordance with the American Conference of Governmental Industrial Hygienists (ACGIH).
These are published in the form of Threshold Limit Values (TLV's) expressed as a Time weighted Average (TWA) of H2S for an 8 hour day/ 40 hour week and a Short Term Exposure Limit (STEL) of 15 minute of exposure no more that 4 times per day.
Until 2010 the limits for unprotected workers was a TWA of 10 Parts per million (PPM) and a CEV of 15PPM. The working practices and provision of protection and detection equipment for the oil & gas industries across Canada are all based on these levels.
Canadian H2S Regulations
Some Provinces (Alberta, Manitoba, Ontario, New Brunswick, PEI, Nova Scotia, Newfoundland/Labrador) and the Federal Government have clauses in their Health & Safety Regulations to automatically incorporate any new ACGIH TLV's.
New Exposure Limits Published
In 2010 the ACGIH issued new TLV's for H2S of a TWA of 1 (compared to 10 previously) and a STEL of 5 (15 previously). ACGIH TLV's are health-based and no consideration is paid to economic feasibility.
Industry Reaction
This could be a huge problem for the oil & gas industry! Many of today's measuring devices are not capable of measuring such low concentrations. Compliance would require major expenditures in personal protective equipment and a significant loss of productivity in affected workplaces.
The H2S Situation in Canada Today
Newfoundland has formally responded to the revised ACGIH H2S exposure levels (see www.enviromed.ca/Documents/Letter2.pdf). This acknowledges the practical problems and states that their OCCUPATIONAL HEALTH & SAFETY Officers will not issue orders under the new TLV's 'until further notice'.
An enquiry to the Ministry of Labour in Ontario elicited this response:
"In regards to the limit for Hydrogen Sulphide the current limit in Ontario Regulation 833 Control of Exposure to Biological or Chemical Agents is 10ppm TWA and 15ppm STEL. The Regulation and Table of Occupational Exposure Limits for Ontario Workplaces can be accessed at: http://www.labour.gov.on.ca/english/hs/topics/oels.php.
In the summer of 2010 the Ministry of Labour consulted on proposed new and revised occupational exposure limits including a proposed updated limit for Hydrogen Sulphide of 1ppm TWA and 5ppm STEL. The Ministry is continuing to review the results of this consultation."
Conclusion
Every employer whose workforce might come into contact with Hydrogen Sulphide must comply with any Regulations that apply. They must also maintain a watching brief on these issues concerning exposure values permitted for their workers.
