The dangers associated with H2S can be life-threatening and depend on the concentration of exposure. (Draeger Safety photo)

Respiratory Protection in Extreme H2S Environments

Given the health hazards caused by H2S, it is of the utmost importance to select a respirator that allows for appropriate protection based on the work environment and correlating standards and guidelines that vary globally.

Hydrogen sulfide (H2S) poses an exceptionally high risk for industrial workers, especially those in the oil and natural gas industry. Oil fields rich in sulfur and H2S can lead to contamination of the ambient air, causing health problems or even fatalities. According to the U.S. Bureau of Labor Statistics, there were 64 fatal occupational injuries involving H2S from 2003 to 2012.

While NIOSH, OSHA, and ACGIH guidelines and standards were developed to protect workers from this life-threatening gas and other work site hazards, it is important to supplement these protocols with additional safety measures and the right protective equipment. This is especially critical when workers find themselves in hazardous environments, such as sour gas-containing oil fields. Therefore, it is imperative that companies conduct their own risk assessments and testing, beyond implementing baseline industry measures. This will help to ensure they are maximizing worker safety through the proper tools and education, which will coincide with the minimization of incidental H2S exposure.

Identifying On-site Risks and Determining Proper Protection
When determining how to minimize the effects of H2S exposure, it is essential to identify potential on-site sources. According the U.S. Environmental Protection Agency, 90 percent of H2S is created naturally, occurring at crude petroleum and natural gas deposits or stagnant bodies of water, such as swamps. H2S results from the breakdown of organic matter. The remaining 10 percent of H2S is manmade, found in the oil and gas, chemical, and pulp and paper industries.

The dangers associated with H2S can be life-threatening and depend on the concentration of exposure. For example:

  • .13 ppm: For H2S, this is the threshold of odor detection.
  • 10-100 ppm: Eye and throat irritation and headaches can occur after one hour of exposure. With continued exposure, a worker may experience nausea, dizziness, coughing, and vomiting.
  • 700-1,000 ppm: H2S can cause unconsciousness and immediate collapse within one or two breaths. Fatality is possible at this level if the worker is not removed from exposure.
  • 1,000-2,000 ppm: Nearly instant death occurs.
  • 45,000 and 450,000 ppm: Concentrations at this level can trigger an explosion.

Given the health hazards caused by H2S, it is of the utmost importance to select a respirator that allows for appropriate protection based on the work environment and correlating standards and guidelines that vary globally. For example, if the work site is based in the United States, OSHA regulations should be followed, and respirator selection will be based on the maximum use concentration (MUC). This is calculated by multiplying the assigned protection factor (APF) by the recommended exposure limit (REL). The APF of a certain class of respirators can be found in OSHA's standard 29 CFR 1910.134, and the exposure limits can be found in NIOSH’s Pocket Guide to Chemical Hazards.

Using this formula for H2S exposure, the following respirator types are suggested for the following specific concentrations:

  • 0-10 ppm: No respirator is needed, below the recommended exposure limit (REL).
  • 10-100 ppm: Powered Air-Purifying Respirator (PAPR), Full Face Mask Cartridge Respirator, or Self-Contained Breathing Apparatuses (SCBA).
  • 100-100,000 ppm: SCBA or Supplied Air in positive pressure mode.

In tandem, you would be smart to conduct your own risk assessment or use a pre-defined checklist of criteria, such as the following NIOSH Respirator Selection Logic1:

  • General use conditions, including determination of contaminant(s);
  • Physical, chemical, and toxicological properties of the contaminant(s);
  • NIOSH recommended exposure limit, OSHA permissible exposure limit (PEL), American Conference of Governmental Industrial Hygienists Threshold Limit Value (TLV), or other applicable occupational exposure limit;
  • Expected concentration of each respiratory hazard;
  • Immediately dangerous to life or health (IDLH) concentration;
  • Oxygen concentration or expected oxygen concentration;
  • Eye irritation potential; and
  • Environmental factors, such as the presence of oil aerosols.

Through using this initial assessment, companies will find that they are on the right path to identifying the most optimal respirator for their work site.

What If Workers Could Be Exposed to More Than 100,000 ppm?
In some circumstances during drilling operations or work-overs of low-producing wells, there could be releases of H2S that well exceed 100,000 ppm. As a company, it is important to perform a risk analysis to determine what the potential exposure levels could reach. If it is determined that workers could be in environments that exceed 100,000ppm, how can you be sure they are still protected, given that the current guidelines only recommend up to 100,000 ppm?

Some manufacturers have performed additional testing on their breathing apparatuses to see if they still protect at higher levels. If they have, ensure the testing was based on a Simulated Workplace Protection Factor (SWPF). If the respirator was tested only with aerosols, this would not represent the molecular characteristics of a gas and should not be used as an evaluation for H2S protection.

A SWPF would involve:

"A study, conducted in a controlled laboratory setting and in which Co (the concentration of an airborne contaminant, e.g., hazardous substance outside the respirator) and Ci (the concentration inside the respirator) sampling is performed while the respirator user performs a series of set exercises. The laboratory setting is used to control many of the variables found in workplace studies, while the exercises simulate the work activities of respirator users."

To mimic the specific safety challenges that occur during H2S exposure, consider using sulfur hexafluoride (SF6), as it behaves similarly to H2S. For example, a third-party test was conducted in a laboratory setting using sulfur hexafluoride (SF6) to measure the SWPF for a leading safety solution company’s full face masks. Using five head forms that were created based on more than 3,000 3D head scans, six test exercises were conducted to simulate an escape situation. The SCBAs were tested against current industry standards, which require an APF of 10,000, as well as the new ISO RPD standard that will be released in 2016. The PF of the tested masks fell between a minimum mean of 152,000 and a maximum mean protection factor of 524,000, with the lowest recorded PF being 100,000. Going back to the MUC formula (MUC = APF x REL), this means that the SCBA provides protection in concentrations well above industry standards.

Note that these tests do not replace OSHA standards and guidelines, but should be used to know that in case of an unexpected high concentration release of H2S, your workers can be protected until they get to a safe zone. If this will be part of your risk assessment or procedures, ensure that you receive the manufacturer’s test results for backup.

As more advanced technology able to withstand the most extreme environments becomes increasingly available, it is critical that companies consider investing in these devices. Not only will the investment demonstrate a company's passion for its workers' safety, but also it could ultimately save its most valuable asset, its workforce, in the event of an H2S incident.

This article originally appeared in the February 2015 issue of Occupational Health & Safety.

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