CSB releases final report on hydrogen sulfide release at Texas waterflood station

THE US Chemical Safety Board (CSB) has released its final report on the 2019 hydrogen sulfide release at the Aghorn Operating waterflood station in Texas, which caused the deaths of two people.

The Aghorn Operating Waterflood Station in Odessa, Texas, receives produced water from around 68 oil wells in the Permian Basin. Aghorn pumps pressurised produced water into oil reservoirs to assist in oil recovery, a technique known as waterflooding.

Produced water usually contains hydrogen sulfide (H₂S) which is a toxic, colourless gas. While it has a smell like rotten eggs, exposure to the gas can cause a person to lose their sense of smell. The National Institute for Occupational Safety and Health (NIOSH) recommends an exposure limit of 10 ppm. An exposure of 100 ppm is considered an immediate danger to life or health, greater than 500 ppm can cause collapse within five minutes, and greater than 700 ppm can cause collapse within two breaths.

A 2017 study found that 85% of Permian Basin natural gas contains a H₂S concentration greater than 100 ppm. There are around 115,000 injection wells across the US.

Multiple safety failings

On 26 October 2019, a worker at the Odessa facility responded to a pump oil level alarm. He did not correctly isolate the pump from the system and at some point a loss of containment occurred, releasing water containing H₂S. The employee was fatally injured from exposure to H₂S. His wife, who came looking for him several hours later, was also fatally exposed to the gas.

The final report from the CSB found several safety issues.

There wasn’t a written procedure for lockout / tagout to deenergise a pump before any work is performed on it. On the night of the incident, the worker didn’t perform the lockout/tagout procedure before working on the pump. He closed the discharge valve and partially closed the suction valve while the pump was still configured to be operated automatically. The pump was then automatically activated at some point, which released water containing H₂S. The CSB was unable to determine if the pump failure and loss of containment happened before the employee arrived or during the pump maintenance.

There was a lack of appropriate site security. The CSB found that H₂S warning signs outside the site were corroded, non-reflective, and unlikely to be seen by anyone in low light conditions. Aghorn’s policy was for the gate to be unlocked and open while an employee was on site. This allowed the worker’s spouse to enter the site to search for him. According to the report, when she hadn’t heard from her husband in a few hours, she drove to the site with their two children – aged six and nine – in the car. She called another worker who was on holiday at the time and he suggested she look in the pump house. He then lost contact with her and notified the emergency services. Her body was found next to that of her husband in the pump house. The emergency services found the children still conscious in the car and brought them to safety. Emergency responders noticed a H₂S concentration of 150 ppm as they approached the pump house. Other measurements weren’t possible, as the levels had exceeded the detector’s capabilities.

The site had a H₂S alarm system which should have caused a beacon light to go off on the top of the pump house as well as trigger an automatic phone notification system. However, the alarm system wasn’t functioning at the time of the incident. The CSB found that the working detectors didn’t communicate with the H₂S control panel and that some detectors were in test mode.

The employee had a personal H₂S detector but wasn’t wearing it at the time. It was later found in his truck, emitting an audible alarm. Aghorn had no policy making it mandatory for employees to wear detectors.

There pump house wasn’t properly ventilated. The CSB found that the two bay doors were only 60% open at the time and it couldn’t determine if fans were operational.

Recommendations

The CSB made numerous recommendations to Aghorn for all of its facilities. These include making personal H₂S detectors mandatory, developing formal site-specific lockout/tagout procedures including training, ensuring appropriate site-specific ventilation, ensuring alarm systems are properly maintained and configured, ensuring alarms are both audible and visible and have multiple layers of alerts, and developing site-specific security programmes to prevent unauthorised access.

In a closing statement at the Public Board Meeting for the incident, Katherine Lemos, Chairman and CEO of the CSB, said: “Even the most basic of protections for workers were not reinforced by Aghorn. Training and management attention to safety items such as wearing a personal H₂S detector is the best and first line of defence in preventing this type of fatality, for workers and public alike. Worker safety must be prioritised especially by those companies with employees working in remote locations.

“The impact of our investigation into this Aghorn event is not just about the unfortunate circumstance of two lives and their families, albeit tragic. This is a call to action for all companies, large and small, to step up to the plate to prioritise the safety of your workers and your community.”