New safety video from CSB highlights tank fill dangers

Article by Helen Tunnicliffe

CBS video still
In a still from the video, the driver is shown being too affected by the chlorine to stop the flow of acid from the truck

THE US Chemical Safety Board (CSB) has released a new safety video about a 2016 incident in Kansas in which a chemical delivery driver connected his truck to the wrong fill line, resulting in a large release of toxic chlorine gas.

The incident, at the MGPI Processing facility in Atchison, Kansas, on 21 October 2016, resulted in 140 injuries, with a number of people admitted to hospital, and 11,000 local residents forced to evacuate or shelter-in-place as the cloud of chlorine gas drifted over the town. A study by the National Association of Chemical Distributors showed that in the US more than 39.9m t of product was delivered to customers every 8.4 s in 2016, giving many opportunities for similar incidents to occur. Since 1 January 2014, eight other similar incidents have caused 44 injuries and the evacuation of 846 people. As such, the CSB has now used the MGPI incident as a case study in its new video, looking at the lessons that should be learnt from it.

CSB chairperson Vanessa Allen Sutherland says in the video that while chemicals deliveries are often considered simple, the volume of chemicals involved means that the consequences of mistakes can be severe.

On the day, the delivery driver, with a routine delivery of sulfuric acid, was escorted to the tank farm by an MGPI operator. The operator unlocked the sulfuric acid tank fill line ready for the driver, told him which was the right line and left him to it. The operator, however, failed to spot that the sodium hypochlorite line, which was just 45 cm away, very similar in appearance and not obviously labelled, was also unlocked. The driver connected his truck’s hose to the wrong fill line, and the two chemicals reacted, releasing the gas. By the time the driver noticed the green gas cloud in the mirror of his cab, the fumes were too thick for him to disconnect the hose, or to stop the flow directly from the side of the truck. The chlorine gas entered the site’s control room through the ventilation system. PPE was stored in a locked cabinet, which could not be opened in time, and the operators were forced to evacuate.

The investigation found that one of the major contributors to the event was human factors, and the interaction of the operator and the delivery driver with the transfer equipment. For example, the CBS investigation found that the proximity of the fill lines greatly increased the chance of such an accident, and noted that they both looked and functioned identically using the same connections. Just one of the five lines in the load area was obviously labelled.

Incident investigator Lucy Tyler said that three main lessons should be learnt. Firstly, all chemical unloading equipment and processes must be evaluated, with safeguards implemented to lower the accident risk, such as physically separating fill lines and properly labelling lines where they connect for deliveries.

In the MGPI incident, the only way to shut down a transfer was manually. However, without the right protective equipment, this was not possible. The second main lesson is that facility managers should consider installing alarms and interlocks within process control systems where feasible to shut down transfers remotely in such an emergency.

Thirdly, facilities and chemical distributors should conduct detailed risk assessments and agree on procedures clearly setting out the responsibilities for all involved. At MGPI, procedures were not followed, but some operators were not aware of them.

“Chemical deliveries are happening every day all around us. Because these deliveries are so common, the CSB strongly urges the managers of facilities and distributors to review and adopt the key lessons from our case study, and work together to prevent future incidents like the one at MGPI,” says Sutherland in the video.

Article by Helen Tunnicliffe

Senior reporter, The Chemical Engineer

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