Opening Live Systems: Treating Every Pipe and Hose as Pressurized

Pipes and hoses rarely announce what's inside them. A line that "was drained yesterday" can still hold trapped pressure, a pocket of toxic gas or hot liquid behind a closed valve. The moment a flange is loosened or a hose is disconnected, all of that has somewhere to go, usually straight towards the person holding the spanner.

So the rule for line breaking is: treat every line as live until you've proved it's safe, and keep yourself out of the line of fire while you do.

What that looks like on the job

• Isolate, depressurise, drain and flush under a permit, then verify that the isolation holds and that hazardous pressure and contents are gone, using the approved verification method for that system, not paperwork alone. A gauge reading zero is not proof on its own.
• Expect the unexpected. Valves pass, drains block and lines can re-pressurise from another source.
• Stay out of the line of fire. Position yourself away from the potential release path, and open the connection following the approved line-breaking procedure, using methods that control any residual pressure or contents.
• Wear protective equipment chosen for what was in the line, not for what you hope is left in it.
• Look after hoses and temporary connections. Use the right material for the chemical, inspect it, and replace it as the manufacturer and your site maintenance programme require.

Real-World Impact

In January 2010, at a chemical plant in Belle, West Virginia, a hose connected to a one-ton tank of phosgene, a gas used as a weapon in the First World War, burst while an operator was nearby. He was sprayed with phosgene and died the next day. The U.S. Chemical Safety Board found that the hose was meant to be replaced every month but had been in service for seven months, and that its type of material was vulnerable to corrosion from phosgene. A more resistant hose had been considered but never used.

Source: U.S. Chemical Safety and Hazard Investigation Board (CSB), DuPont Belle investigation (2011)

Reflective Questions

• Before you open a line, what evidence do you have that it's empty, beyond someone telling you it is?
• Where would you be standing if the joint you're loosening let go?
• Do we know when each of our hoses and flexible connections is due for replacement, and does it actually happen?