MSHA bulletin addresses pump explosions

The Mine Safety and Health Administration is alerting enforcement personnel, mine operators, independent contractors and equipment manufacturers of the potential safety hazards related to catastrophic failure (explosion) of pumps and associated components.

Catastrophic failure of pumping systems can occur due to an overpressure condition created within the pump when fluid flow through the pump is lost, resulting in the overheating of any trapped fluid within the pump case. Loss of fluid flow can occur due to a blockage in the discharge and/or inlet piping. It can also occur due to a malfunctioning or inadvertently closed valve.

Catastrophic failure can also occur due to a sudden surge of fluid through the pump or into downstream components after a delay in acquiring fluid, especially when the pump is turning at or near rated speed.
Catastrophic failure of pumping systems can be reduced by detecting one or more loss-of-flow conditions. Loss-of-flow conditions can be detected by 1) using direct fluid flow measuring equipment, 2) measuring the pump motor current draw (amperage) to detect loss of pump load, and 3) measuring the pump temperature to detect overheating of the fluid. Monitoring pumps for loss of flow will help detect dangerous conditions resulting from malfunctioning equipment, loss of fluid pickup or plugged or restricted discharge and/or inlet piping.
 
Flow sensing devices can be installed that automatically shut down the pump if flow stops for any critical period of time. These devices can be simple paddle switches in a clean fluid such as well water, or they may be more sophisticated devices that do not come in contact with the fluid, such as magnetic flow meters for aggressive fluids such as slurries.

Motor current sensing devices, which alert and automatically shut down the pump whenever the motor current draw drops below the expected operating range for any critical period of time, can be installed in the system. Pump motor current typically drops when the feed is reduced and the pump ceases to pump material.

Thermal sensing devices can be installed to measure the temperature of the liquid in the pump volute. A warning temperature and an automatic pump shutdown temperature can be programmed into certain types of controllers. The American Society of Mechanical Engineers requires two temperature sensors, one primary and one backup, when used as a safety device in this manner. Some types of these devices can be attached to the pump without drilling or tapping. Some programmable controllers allow for multiple set points such as alarm and shut down, so that remedial action could be performed to alleviate a problem before tripping the device. Mine operators should contact their suppliers or the pump manufacturers for further assistance in identifying and implementing appropriate pump safety controls.

There have been two fatalities, one serious accident and one non-injury incident over an eight-year period due to pumps and similar equipment exploding.