Last reviewed 16 March 2021

The Health and Safety Executive (HSE) has issued a safety alert after a serious incident involving the failure of a road tanker pressure/vacuum relief valve.

In the safety report the HSE explains that:

“Bulk transport containers used for flammable, corrosive and toxic liquids and gases will normally have a pressure/vacuum relief valve fitted to prevent damage to the tank from changes in the internal pressure. These valves should be inspected and maintained in line with the manufacturer’s instructions.”

The incident occurred in April 2020 and an investigation uncovered evidence that a pressure/vacuum relief valve had undergone an unauthorised modification by a third party.

The investigation found:

“Some valve designs require a special tool to dismantle them for servicing. Investigations by HSE found a technician had welded a nut on to the top of the valve to allow it to be dismantled without the use of a special tool. The nut prevented the free movement of the valve stem, resulting in the valve sticking open and releasing hazardous vapours.”

This modification prevented the valve’s safe operation.

The HSE advises:

“Visually inspect the pressure/vacuum relief valves fitted to tank containers (often referred to as iso-tanks) and road tankers used to transport dangerous substances. The inspection should establish if there have been any unauthorised modifications made to the valve, particularly items fixed to the valve to allow for easier dismantling.”

The safety alert van be found on the HSE website.