Pressure build-up in silos

Overview

Several mines and quarries have cement and fly-ash silos that service pugmills, concrete plants and paste fill plants. These silos normally have over-pressure relief valves and venting filters. Over-pressure relief valves are designed to release pressure built up in silos. If the pressure is not released the filters and/or the silo can be damaged. The filters may be bag or cartridge types that filter vented air from silos when cementitious products are pumped in.

Where is the risk?

There have been high-potential incidents at Queensland mines and quarries where pressure has built up in silos to a point where filters have been dislodged and filter covers thrown considerable distances, landing dangerously close to workers (see images).

Common contributing factors were:

• poorly maintained filters and pressure relief valves
• not enough control over pressures being used by tanker drivers to fill silos
• poorly designed pressure relief valves and piping systems.

Recommendations

1. Over pressure relief valves and piping systems be designed fit-for-purpose, be easy to check and maintain, and account for supplier-recommended discharge pressures.
2. Regular checks and maintenance be carried out on the filter and pressure relief systems.
3. Random checks be enforced to ensure contractor tanker operators discharge cementitious products in accordance with safe work procedures, including monitoring recommended pressures during discharge.
4. Pugmill, paste fill plant and concrete batching plant operators be adequately trained and competent in procedures, including maintenance of pressure relief systems and silo filling.
5. Tanker drivers be adequately trained and competent to fill silos from tankers, including in managing recommended pressures for discharging cementitious products.
6. Over pressure regulators and/or alarms be installed on silos.
7. Appropriate signage be installed to indicate pressures to be used with filling individual silos.

Authorised by Rob O'Sullivan - Chief Inspector of Mines

Contact: minesafetyandhealth@dnrm.qld.gov.au

Issued by Queensland Department of Employment, Economic Development and Innovation