We’ve all caught a whiff of hydrogen sulfide gas, with its odor of rotten eggs. It’s a colorless, extremely toxic gas, produced from decaying organic matter. It is detectable at concentrations as low as 0.13 parts per million, but a temporary loss of smell (“olfactory fatigue”) can occur at levels of 100 to 150 ppm, which can result in the mistaken, and potentially lethal, belief that the gas has cleared away.
The applicable OSHA construction standard limits H2S exposure to 10 ppm, with an 8-hour limit. Exposure to levels above 300 ppm can cause coma in less than 20 minutes, and serious eye damage, while 500 ppm can cause loss of coordination and unconsciousness within 5 minutes. Exposure at levels over 1,000 ppm can cause almost immediate coma and death. The inhalation of H2S can also cause fluid to build up in the lungs (pulmonary edema) 24 to 72 hours after exposure. Other effects of exposure include nausea, tearing of the eyes, conjunctivitis, headaches, loss of sleep, bronchial construction, fatigue, drowsiness, loss of appetite, headaches, irritability, throat irritation, and coughing.
In the construction industry, H2S sickness and fatalities are most commonly associated with confined spaces (pits, manholes, tunnels, and wells) and work in or near sewers or landfills. Work in marshy areas and in hot weather (which accelerates the breakdown of organic material) also heightens the risks of exposure. In researching this article, I read a nightmarish account of how H2S (a/k/a “swamp gas”) was released as workers drove test pilings into a 27’ deep pit, excavated on marshy land on a New Jersey barrier island. A worker collapsed into the pit, and others attempting his rescue were sickened. Several were hospitalized, one remaining in a coma for five days. A local police officer fell unconscious, and drowned in water that had accumulated at the bottom of the pit, and approximately 30 area residents were seen in the local emergency room.
The speed at which exposure can cause unconsciousness is sometimes referred to as hydrogen sulfide’s “knockdown effect,” and it can produce both an inability to escape the area of exposure, and serious injuries from falls. Even workers who do not wholly lose consciousness can quickly become unable to extricate themselves, or respond to instructions. In some cases, workers who do lose consciousness due to inhaling H2S, suffer longer-term health effects, including headaches, reduced attention span and memory, cardiovascular and motor problems.
In addition to being highly toxic if inhaled, H2S is highly flammable and explosive. As a liquid, hydrogen sulfide can cause frostbite and, as a gas, it burns, and produces sulfur dioxide and other toxic vapors and gases.
To protect your employees, you need to ascertain whether hydrogen sulfide is present and, if it is, at what levels. OSHA recommends a “Job Hazard Analysis,” to identify sources of H2S, evaluate potential respiratory, fire, and explosion hazards, and devise control strategies. A “qualified person” should use proper test equipment (e.g., detector tubes, direct reading gas monitors, alarm-only gas monitors, and explosion meters) to monitor the air before, and at regular times during, any work activity during which H2S exposure is possible.
OSHA commends OSHA Sampling and Analytical Method 1008, which involves specially-constructed H2S samplers, containing silver nitrate coated silica gel, and NIOSH Method 6013, in which air samples, collected with a glass tube and sampling pump, are analyzed with ion chromatography.
Whatever testing method you select, do not rely on your sense of smell to monitor the air Eliminating the source is obviously the ideal strategy — but, if that is not possible, then engineering controls, administrative controls and safe work practices must be effectuated.
Exhaust and ventilation systems are a primary method of reducing H2S levels. Because H2S is flammable and corrosive, it is essential that your system be:
When work is being performed in confined spaces, ventilating systems should be operated continuously, and in accordance with all relevant OSHA standards.
If engineering and administrative controls do not suffice to reduce exposure levels below OSHA’s 10 ppm limit, the employer must provide respiratory protection and other personal protective equipment, including eye protection and, possibly, fire-resistant clothing. For exposures below 100 ppm, use an air-purifying respirator, equipped with specialized canisters or cartridges for hydrogen sulfide. A full-face respirator will provide eye protection.
Exposures above 100 ppm are “IDLH,” which means “Immediately Dangerous to Life and Health.” At these levels, employees need a full-face pressure demand, self-contained breathing apparatus, with a minimum service life of thirty minutes, or a combination full-face pressure, demand-supplied respirator, with a self-contained, auxiliary air supply.
It is mandatory to complete a PPE hazard assessment and equipment selection process, in compliance with OSHA regulations before beginning any work activities in which H2S may be encountered. You need to comply with OSHA’S Respiratory Protection standard (29 C.F.R. 1910.134) which includes, among other things, proper respiratory selection, fit testing, medical evaluations, and training. Respiratory equipment must also be inspected regularly prior to use, and worn or damaged equipment removed from service. OSHA also publishes a “Small Entity Compliance Guide for the Respiratory Protection Standard” (call 202-693-2300 for help in accessing this material).
Needless to say, if your employees work in confined spaces or are otherwise at risk of H2S exposure, they must be trained about H2S hazards, and how to control them. Training topics should include sources of exposure, symptoms, detection methods, exposure limits, protective workplace practices, emergency plans, rescue techniques and first aid, and confined space procedures.
It is critical that employees be trained, also, in rescue procedures, since there are many stories of multiple fatalities occurring when would-be rescuers are themselves overcome by H2S while attempting to help others. Rescuer protection should include positive-pressure, self-contained breathing apparatus, and a safety line, to allow for rapid exit.
Paying special attention to hydrogen sulfide is a “no-brainer,” if your trade involves work in confined spaces, or in proximity to sewers or landfills. There are other contexts, however, in which exposure is possible (I suspect the workers on the barrier island in New Jersey did not anticipate encountering it) and it is such dangerous, nasty stuff that air monitoring (if perhaps not the full panoply of preventative measures) is a good idea, even if you’re not working in manholes or other confined spaces, where decaying organic matter is likely to be found.
A review of your operations for possible exposure to hydrogen sulfide is an opportune time to review, and to ascertain that you are in compliance with, the updated OSHA rule for construction work in confined spaces, which became effective in August 2015. The final rule is available online at http://osha.gov/FedReg_osha_pdf/FED20150504.pdf