By Heather Douglas
Many mature Canadian oil and gas fields contain high concentrations of hydrogen sulfide (H2S). Since high levels are life-threatening, corrosive, and flammable, the exploration and operation of these fields must follow strict safety precautions. Any leak containing high concentrations of H2S can cause death within seconds. To ensure workers are given timely alerts, their gas detection devices must be robust, withstand wide temperature swings, and have an almost instantaneous response time so they can escape safety or be rescued.
In March, 2017 Enform, the upstream industry’s advocate for the continuous improvement of safety performance headquartered in Calgary, AB, issued a report saying that three workers had been rendered unconscious by inhaling H2S. Fortunately, they were quickly evacuated, regained consciousness on their own, treated by the onsite medic, then transported to a regional medical facility for evaluation. All three were back at work the same day.
Enform says workers were involved in a 500 litre, 15 per cent hydrochloric acid tubing pickle on a sweet well. “The tubing used in this sweet well had previously been used in a sour well. During reverse circulation from the well to an open top rig tank, four workers were on top of the tank to watch the returns. A fifth worker, the derrick-hand, was in full chemical protective equipment (PPE), including self-contained breathing apparatus (SCBA) preparing to add soda ash into the trough to neutralize the acid returning to the tank.“After pumping about four cubic metres of water down the casing, returns came back “dark and gassy. As the degasser line was opened the rig four-head lower explosive limit (LEL) monitor and the workers’ personal H2S monitors sounded.”
Everyone evacuated from the area, except for three workers working on top of the tank, who made it to the ground before collapsing unconscious. Someone sounded the man-down alarm. The derrick-hand, wearing the protective gear and breathing tank, pulled the trio to safety.
Enform’s subsequent investigation reported the crew was unaware the tubing had been used in a sour well. “Scale in the tubing contained iron sulphide (FeS) and reacted with the acid pumped through the tubing. Thus, H2S gas was released to the atmosphere when the returns reached the rig tank. The three workers were not wearing adequate PPE to protect them from this hazard.”
No one considered the potential of an H2S release because the operator believed the sour zones had been safely cemented off and the crew was working on a sweet well. Nor did anyone contemplate the risk of acid reacting with iron sulphide and generating H2S.
What makes H2S so dangerous? It is a toxic, colourless gas that smells like rotten eggs. However, it numbs the olfactory nerves at a mere 100 parts per million (ppm), and anyone who breathes in concentrations higher than 1,000 ppm is immediately dead. It is also high flammable, and self-ignites at a temperature of 270 Celsius. H2S can trigger spontaneous combustion, explosions, and detonations if its encounters peroxides, bromates, ammonia, or other chemical substances. And, if that’s not enough, when H2S combines with air, humidity, or moisture it can corrode metals – tanks, vessels, and pipes – as it forms sulfuric acid.
Why is detection so important? The oilpatch is a dangerous workplace so the immediate discovery of a sour gas leak is critical to save lives. Sensors need to be calibrated to quickly sound alarms. Ambient H2S concentrations in Canadian fields are frequently found in the three to five ppm range, while the normal levels of most sour gas facilities fluctuate between one and three ppm. Most emergency response plans (ERPs) are triggered at 10 ppm when everyone is required to evacuate to a safe muster point.
Why is practicing a safe escape critical? To keep workers attuned to personal safety when confronted by an H2S incident, it’s important they have easy access to escape respirators which they can put on to evacuate without harm. Too often someone panics so it’s important to train employees on how to use safety equipment, how and where to muster, techniques to rescue in a man-down situation, how to give first aid.
Hydrogen sulphide is a growing challenge in the oil and gas industry. There are solutions to ensure the safety of every worker who deals with this toxic gas.
H2S First Aid:
General
1. Know the typical symptoms of H2S poisoning – nausea, headaches, delirium, disturbed equilibrium, tremors, convulsions, skin and eye irritation; inhalation of high concentrations can produce extremely rapid unconsciousness and death.
2. Be prepared to sound the alarm and initiate the emergency response plan.
Specific
1. Protect yourself first by putting on an escape respirator.
2. Rescue colleagues from contaminated area – lead them to fresh air and keep them warm.
3. Call the onsite medic or emergency doctor.
4. If victim stops breathing, ventilate them by machine – never inhale the breath of the injured person.
5. If victim has skin irritation – immediately remove clothing, bath the contaminated skin with clean water, and consult a medic or doctor; keep person warm and dry and use only sterile dressings.
6. If casualty has eye injury – rinse injured eye for at least 10 minutes under running water while protecting unharmed eye.
#HSE #Health #Safety #Environment #Canadian #OilandGas #H2S
