SAFETY BRIEFING 1: Pressure relief valve near-miss event
Ready-mix, concrete and block works have silos on-site that are pneumatically filled from road tankers. Many of the sites have silos fitted with pressure relief valves as their only protection from over-pressure.
The photographs show how they can be rendered completely ineffective by constant use and poor maintenance. Pressure relief valves are continuously relieving pressure without the reason being investigated or the cause eliminated. The road tankers are capable of blowing product into the silos at pressures as high as 2 bar.
The silo, however, is not a certified pressure vessel and is at risk of rupture at any pressure above 1psi. An effective silo protection system provides automatic closure of the delivery valve. Lack of this has resulted in silos being ruptured and filter systems being ejected from the silo roof.