Gas detection in the oil and gas industry: risks, European framework and US references

What is the status of each rule?

1Gases and atmospheres at risk

Three hazards combine: the flammability of hydrocarbons, the toxicity of gases such as hydrogen sulfide (H₂S), and oxygen deficiency.

H₂S is colorless, highly toxic, flammable and heavier than air: it accumulates in low points and confined spaces. The OSHA eTool cites deaths from 700 to 1,000 ppm and near-instant loss of consciousness at 700 ppm and above. NIOSH sets the IDLH value (immediately dangerous to life or health) at 100 ppm and gives a lower explosive limit of 4.0%. The sense of smell tires quickly: it cannot be used to detect a continuous presence of H₂S. Combustion produces sulfur dioxide (SO₂), which is also toxic.

For hydrocarbon vapors, API RP 54 defines an atmosphere as hazardous notably below 19.5% or above 23.5% oxygen, or above 10% of the lower explosive limit (LEL).

2Where and when the risk arises

• Drilling and well servicing: H₂S may be present. API RP 54 refers to API 49, 55 and 68 for these environments.
• Flares: H₂S and SO₂ emissions are possible there (OSHA).
• Manual tank gauging and sampling: when the hatch is opened, pressure can release a plume of vapors (NIOSH).
• Confined spaces: API RP 54 provides for an atmospheric test before entry (oxygen, flammable gases, toxic contaminants), then continuous monitoring during occupancy.

3European framework: legal requirements

RequirementDirective 1999/92/EC (worker protection)

Fifteenth individual directive adopted under framework Directive 89/391/EEC. It requires the employer to:

• take technical and/or organisational measures, in this order: prevent the formation of explosive atmospheres, avoid their ignition, mitigate the harmful effects of an explosion (Art. 3);
• assess explosion risks (Art. 4) and classify the places concerned into zones (Art. 7, Annex I): zone 0 (explosive atmosphere present continuously, for long periods or frequently), zone 1 (likely to occur occasionally in normal operation), zone 2 (unlikely to occur, and brief if it does);
• draw up, before work begins, an explosion protection document, kept up to date (Art. 8);
• provide training, written instructions and work permits where that document requires them (Annex II, Part A);
• unless the document provides otherwise, select equipment according to the zone (Annex II, Part B): zone 0 → category 1; zone 1 → categories 1 or 2; zone 2 → categories 1, 2 or 3. The annex refers to Directive 94/9/EC, of which Directive 2014/34/EU is the recast.

RequirementDirective 2014/34/EU (equipment)

• It covers equipment and protective systems intended for use in potentially explosive atmospheres, their components, and certain safety, controlling or regulating devices used outside those atmospheres (Art. 1).
• Categories 1, 2 and 3 of group II correspond to a very high, high or normal level of protection (Annex I).
• Whether a given detector falls within its scope depends on its design and use: it is for the manufacturer to specify.

These directives do not mandate a type of detector. They require risk assessment, zoning and suitable equipment. National laws may detail the transposition.

4US references

RequirementFederal legal requirement

For H₂S in general industry, OSHA sets a ceiling of 20 ppm. A peak of up to 50 ppm is tolerated for 10 minutes at most, only if there is no other measurable H₂S exposure during the eight-hour workday. In construction and shipyards, the limit is an average of 10 ppm.

RecommendationRecommendations

• NIOSH recommends a ceiling of 10 ppm over 10 minutes.
• The OSHA eTool describes 10 ppm as an alarm threshold commonly used by industry.
• The eTool also recommends personal and area monitoring, a personal detector placed near the breathing zone, and calibration and maintenance according to the manufacturer.
• The eTool states that a detector alone is not enough against near-instant collapse at high concentration.
• For hydrocarbon vapors, NIOSH recommends calibrated multigas detectors (LEL and oxygen).

Industry practice

API RP 54 (4th edition, February 2019) is a recommended practice: whether it is binding depends on its adoption by a regulator or a contract.

5Operation and good practice

• Test the atmosphere before entering a confined space, then monitor continuously (API RP 54).
• Calibrate and maintain detectors, and know how to respond to alarms (OSHA eTool, NIOSH).
• Avoid working alone in at-risk areas (NIOSH).
• Use suitable respiratory protection: filtering respirators do not protect against ethane, propane and butane, or in oxygen-deficient atmospheres (NIOSH). API RP 54 provides for self-contained or supplied-air breathing apparatus when tests reveal toxic gases at IDLH level or insufficient oxygen.

6Lessons learned: manual tank gauging

The MMWR report of 15 January 2016 records 9 deaths of oil and gas extraction workers, from January 2010 to March 2015.

Facts documented in the report

• 5 deaths during fluid sampling and 4 during manual tank gauging.
• All the workers were alone.
• Measurements available in two cases: about 11% oxygen near the tank opening, with hydrocarbon gases and vapors above the LEL, and 7% oxygen in another case.
• Only one worker in nine wore a respirator, and it was not suited to these concentrations.

Suspected factors, not established case by case

• A link between the deaths and exposure to hydrocarbon gases and vapors and to oxygen deficiency, retained by the report as the probable cause.
• A mechanism of sudden cardiac death at very high concentration (above 100,000 ppm), notably with pre-existing coronary disease: death certificates mention cardiovascular diseases.
• The NIOSH post on the first cases rules out H₂S as a cause.

RecommendationNIOSH recommendation

Replace manual gauging with electronic systems (sonar, in-line flow meters) or, failing that, limit manual gauging by procedure.

Sources

European Union

• Directive 1999/92/EC of 16 December 1999 (EUR-Lex)
• Directive 2014/34/EU of 26 February 2014 (EUR-Lex)

United States

• OSHA: H₂S exposure limits
• OSHA: eTool, H₂S monitoring
• NIOSH: Pocket Guide, hydrogen sulfide
• NIOSH: science blog, tank gauging
• CDC: MMWR report of 15 January 2016
• API RP 54, 4th edition