Stink damp

On May 22, 2014, Michael Bunz died while working alone at an oil battery in southeast Saskatchewan. The 38-year-old man from Wawota, Sask., sold chemicals to the oil industry and he regularly conducted testing at well sites. He left behind his wife and two daughters.

The incident is still under investigation by the provincial occupational health and safety branch, so it is unclear exactly what happened, but the coroner’s office confirmed hydrogen sulphide (H2S) was the cause of death.

“I got a phone call from his boss that he was hurt, and he was gone,” Kara Bunz told the CBC. “I got the autopsy report, so I know 100 per cent that it was H2S gas.”

H2S — also called sour gas, sewer gas and stink damp — is a highly toxic gas that occurs naturally in the earth in petroleum and natural gas. It is one of the most deadly occupational hazards in the oil and gas industry — too much H2S can kill a worker in a few seconds.

Oil and gas workers are exposed to H2S most often during drilling and production of natural gas, crude oil and petroleum products. It is also found in refineries, oil and gas wells, battery stations and pipelines.

Truck drivers transporting fluids that H2S has been dissolved into have some of the highest fatality rates for H2S. 

Exposure limits

The eight-hour occupational exposure limit (OEL) for H2S in Alberta is 10 parts per million (ppm) and the ceiling is 15 ppm. In British Columbia., the OEL is a ceiling limit of 10 ppm. In Saskatchewan, the eight-hour average contamination limit is 10 ppm and the 15-minute limit is 15 ppm.

At just 20 ppm, exposure to H2S can cause eye, nose, throat and lung irritation, digestive upset and loss of appetite.

H2S levels of 100 ppm and higher are considered immediately dangerous to life and health, which is much lower than many other toxic gases.

“H2S can be a lethal gas in very small quantities and that’s why it attracts so much attention and so much caution,” says Cameron MacGillivray, president and CEO of Enform, the safety association for the upstream oil and gas industry, headquartered in Calgary. “We’re talking about very, very small concentrations presenting a significant human health risk.”

Exposure of 200 ppm can cause major irritation of the nose, throat and lungs, along with headaches, nausea, vomiting and dizziness. Pulmonary edema (fluid in the lungs) can also develop.

Above 500 ppm, workers may experience sudden collapse (knockdown), unconsciousness and death.

“The big problem with H2S is it’s a nerve gas; that’s what’s unusual about it. It affects the ability of the central nervous system and your body to use oxygen… and that can lead to unconsciousness and, ultimately, death,” says Arliss Levine, safety consultant and trainer for Allstar Enviro Safety in Calgary.

Workers who are exposed to concentrations above 500 ppm and survive may recover completely or suffer long-term health effects such as fatigue, anxiety, irritability or impaired learning and memory, according to Work Safe Alberta. Workers who experience knockdown have a greater chance of having permanent effects to the respiratory system such as shortness of breath, wheezing, chest tightness and permanent lung damage.

Long-term exposure to H2S has been reported to cause low blood pressure, headache, nausea, loss of appetite, eye inflammation and chronic cough.

“Sustained exposure to H2S can affect the lung function over the longer haul, it can affect the respiratory system in general and the cardiovascular system or blood supply system,” says MacGillivray.

Engineering controls

Every employer in the oil and gas industry must conduct a hazard assessment with worker input to determine where workers are most likely to be exposed to H2S, and then consider the different controls that need to be put in place. They should consider engineering controls to remove the substance or create a barrier between the worker and the toxic gas, such as ventilation and closed systems that vent to a flare, according to WorkSafeBC.

Fortunately, there are a lot of engineering controls in the design of drilling operations that minimize the chance of H2S being released at the surface, such as the types of drilling fluids used, well control, blow out preventers, annular bags, well service equipment and piping.

Treatment methods are also used to remove H2S from liquid gas streams. For example, ammonia is a “scrubber” gas that is used to knock out H2S from the gas stream, says David Chalmers, president and general manager of Trinity Safety & Training in Saskatoon.

“We would put on, say, a 400 barrel tank that can have H2S in the tank, but in order for it to not come out of the vent and expose workers, it needs to go through the ammonia tank to knock out the H2S.” 

Monitoring systems

While H2S has a strong smell of rotten eggs, workers should never rely on their noses as reliable monitors for the gas. Humans have a wide range of sensory abilities so some people may not be able to smell it at all, while others can still smell it at fairly high amounts, says Levine. In general, the sense of smell is blocked at 150 ppm.

“Once you smell it, it’s in your blood stream so it’s sort of like tasting a poison food to see if it’s safe,” she says. “Once it gets into your system, we have a poor sensory threshold for sulphur and it shuts off your ability to smell it… and so you think it’s gone away, but that is a bad idea because it’s probably increasing.”

If workers are able to smell the gas, they should get out of the area immediately.

One type of gas monitoring predominant throughout the oil and gas industry is electronic personal devices. These are worn by the worker and may just monitor for H2S, but often they have multiple heads to monitor carbon monoxide, oxygen deficiency or explosive atmospheres.

Portable monitors are also available that can be carried to the work site and moved with workers. If the alarm goes off, it would alert all the workers in the immediate area that there is a threat.

There can also be a fixed monitoring system throughout the plant that would send site-wide warning systems if H2S over a certain level is detected. These are often found in gas plants, separator buildings, process buildings and compressor buildings. They can shut down the area from a distance, pull out gas and pump air in and call emergency services to go to the site.

In the past, gas detector tubes were used but these have gone by the wayside as they do not provide real-time gas monitoring.

Employee education

Training workers on H2S is crucial. The industry standard for all workers in the field is Enform’s H2S Alive course. More than 170,000 workers took the course in 2014 alone.

“Anyone who has the chance of exposure to H2S in the industry should be taking this course and, by in large, that covers just about everybody. The industry really has adopted it. The universal approach to it is this is a standard course you need to take if you’re going to be in the industry,” says MacGillivray. “Even if the job is not today being exposed to it, tomorrow you might be in a slightly different job or encounter a situation where H2S exists.”

The full-day training course covers the physical properties of H2S, where workers may encounter it, health hazards and what concentrations may become a risk. Workers learn how to protect themselves as well as how to perform a rescue. They learn how to use and properly don a self-contained breathing apparatus.

Workers are required to recertify every three years.

“What we have an issue with is new workers that don’t understand H2S and until they see (how dangerous it is) they don’t believe it, and then we have complacent workers with many years in the industry and they tend to get too overconfident,” says Levine.

Employers should provide workers with written safe work procedures. It’s also important for employers to clearly label all piping and valves that carry H2S, and wherever an H2S buildup or leak is possible, warning signs must be posted.  

Protective equipment

H2S has a very wide range of flammability — the lower explosive limit is 4.3 per cent and the upper is 46 per cent — so workers are required to wear flame retardant coveralls. 

In areas of high H2S levels or where an leak has occurred, workers must wear approved respiratory protection. A positive-pressure supplied-air breathing apparatus (SABA) is required for work areas where H2S exceeds the eight-hour OEL or the ceiling limit. This respirator would be mostly used for work-related purposes, such as inside confined spaces, vessels or tanks.

A positive-pressure, self-contained breathing apparatus (SCBA) would mostly be used for doing rescues and independent work for exposures at or above 100 ppm.

“(H2S Alive) provides very basic training but the expectation is that the company tops up that training. (Training providers) kind of show them which end is up — they’re certainly not going to be proficient operating that equipment until they get onto a job site,” says Chalmers. “We do see companies doing more and more drills; that is far more frequent now than it was 15 years ago.”

In Saskatchewan, workers are required to receive training every six months on how to operate a breathing apparatus if they are required to wear it in an emergency application — a standard that should be adopted in other provinces as well, says Chalmers.

Employers should provide workers with a written emergency response procedure. If a person has been exposed to H2S and is down, a rescue operation will need to be performed and there are seven main steps for a response plan workers should follow, from evacuation to medial aid (see sidebar).

A key part of a responder’s assessment is to determine if a rescue can in fact be completed. Sometimes performing a rescue is too high risk. To determine if it is safe, rescuers should examine the levels of H2S that their monitors are showing and assess the situation, including how many people are down and how many are available to rescue.

“Very often when we have an incident like this, people are so keen to get in and help people that they inadvertently put themselves at risk by not taking time to don their own equipment, assess the situation and move people away from the risk,” says MacGillivray. “Sometimes, with the best intentions, a followup individual has put themselves in a bad situation.”

This article originally appeared in the August/September 2015 issue of COS.