Safety alert issued after overfill protection system fails during testing

WorkSafe Victoria recently issued a safety alert reminding vehicle owners, operators, and technicians to ensure road tank vehicles have the correct compartment probe length installed in the overfill protection system to prevent a loss of containment of dangerous goods.

The alert was issued following an incident in which the regulator recently attended a full function test of a dangerous goods tanker, which included testing the compartment overfill protection system with water.

During testing, the overfill protection system did not stop the filling process. As a result, the compartment overflowed from both the vapour recovery line and the compartment vent.

Testing identified the overfill protection fault. Without testing, this fault could have later resulted in the loss of containment of dangerous goods, risking the driver, the filling operator, and the public’s safety.

The road tank vehicle was fitted with an overfill protection system as part of the earthing integrity system, and the following were tested and deemed functional before use.

The road tank vehicle compartment was filled to 90 per cent of the safe fill level as part of the full function testing. The filling flow rate for these road tank vehicles is typically 500-700 litres per minute.

The investigation identified the overfill protection probe was too short (in length). As a result, it did not detect the fluid in time to shut down the transfer before overflowing the compartment. This fault was only detectable through full-fill testing.

The alert said road tank vehicles should not be filled at more than 80 per cent capacity to prevent the load from becoming unstable. A loss of containment event can occur if an overfill protection probe is fitted incorrectly to the road tank vehicle or if the length does not comply with the manufacturer’s design to prevent overfilling.

A loss of containment places the driver, the filling operator, and the public at risk of exposure to hazardous substances and dangerous goods.

Overfill protection systems need to be tested and inspected in accordance with Australian Standard (AS) 2809 - Road tank vehicles for Dangerous Goods, Part 1: General requirements for all road tank vehicles.

The full-fill function testing should occur as part of the inspection and/or testing of the compartment hatch and its assemblies. The testing needs to occur regularly on each road tank vehicle.

Where overfill protection systems or probes need replacing, the safety alert said the work should be undertaken:

• By a suitably qualified service technician.
• In accordance with the manufacturer’s specifications.
• In a workshop environment (avoid undertaking work in the field).

Furthermore, duty holders with management and control need to have a system of work in place to ensure the overfill protection probe is operational. This includes ensuring:

• The overfill protection system is installed as per the manufacturer’s installation specifications.
• The overfill protection probe is set to the correct length for each road tank vehicle compartment (measured from the bottom of the hatch to the bottom of the probe)
  through engineering calculations.
• The overfill protection systems probe length is accessible to service technicians and others who may need to know this information. The probe length detail, of each road tank vehicle, can be recorded on a label adjacent to each compartment.