Fine adjustment Valve A (Figure) had to be changed. So, the operator closed the valve below it. To complete the isolation, he intended to close the valve on the other side of the room in the pipe leading to Valve A. However, he overlooked the double bends overhead (which are in the horizontal plane) and closed Valve B, the one opposite Valve A. Both of the valves that were closed were the third from the ends of their rows. When a mechanic unbolted the topwork of Valve A, the pressure of the gas in the line caused the topwork to fly off and hit the wall, fortunately missing the mechanic. It could have killed him. How can we prevent such an accident from happening again?
Several simple solutions available
1. The ideal solution would be to rearrange the pipework so that valves in the same line are opposite each other. To do so on the existing plant might be impractical, but the point should be drawn to the attention of the design organization and noted for the future. Designers' errors produce traps into which operators can fall.
2. Revising the instructions to make the duties of people who prepare equipment for maintenance clearer is a usual reaction, but will unlikely have any effect. If instructions are made longer and more detailed, fewer people will read them.
3. Color coding of the pipes or valves would be the most effective solution.
In some companies, the mechanics are required to check the isolations before starting work. However, this can be difficult if the isolations are some distance away. The incident should be given widespread publicity, not just immediately afterward, but repeatedly in the future as part of the training of people authorized to issue permits-to-work.
Trevor A. Kletz, safety consultant
Perform a HAZOP
Tim Goebel, senior staff engineer
CITGO Petroleum Corp., Lake Charles, La.
Label the lines
Dawn Morris, process engineer
GB Biosciences, Houston, Texas
Robert Inouye, lead operator
Tessenderlo Kerley Inc., Burley, Idaho
Danger of expanding liquid
Mike Moore, corporate engineering manager
Mapei Corp., Deerfield Beach, Fla.
Label with line numbers
Terry V. Molloy, P.E., president
CMES Inc., Novato, Calif.
Key lock mechanism
Swami R. Swaminathan, principal instrumentation engineer
Technip USA, Claremont, Calif.
Add a check valve
Kirt Matson, formulation plant manager
Van Diest Supply Co., McCook, Neb.
Martin West, maintenance engineer
Sunoco Inc., Tulsa Refinery, Tulsa, Okla.
Labels require care
Brad Stanley, chemical engineer
Purafil Inc., Doraville, Ga.
Loosen one bolt at a time