On a petrochemical platform, 2 subcontracting employees removed in the workshop the strainer from a pressure bottle (i.e. anti-pulsation accumulator on the fire circuit, under 7 bar of pressure, in the aim of avoiding a water hammer effect on the network) in order to verify its internal condition as part of a periodic inspection, when the strainer was ejected striking an employee. The victim was airlifted by helicopter for emergency hospital treatment for the serious trauma he had sustained to the shoulder and thorax. The other employee, in a state of shock and diagnosed with auditory lesions, received care at the site’s infirmary before being transported to hospital. The accumulator (a water surge vessel built 18 years prior and fitted with an internal bladder) had been depressurised beforehand; given the lack of back pressure from the fire network water, this bladder filled the entire internal volume and was only confined by the strainer. Upon removing the set of flanges and sealing joint, the pressurised bladder propelled the strainer. The bottle enclosure did not burst. The most recent periodic inspection certificate from 3 years prior made no mention of any anomaly. Documents furnished by the manufacturer, which listed the preventive measures to be carried out before equipment disassembly (i.e. nitrogen discharge from the bladder before removing the locking nut on the device housing and retention ring on the strainer), had been delivered to the subcontractor yet were not consulted before the mission, given that the subcontractor had already performed such operations on this type of equipment several times.