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
F.E. Lewis, discipline authority, process engineering
BP America Inc., Houston, Texas
Add bleed valves
Dan Iezek, manager, engineering and maintenance
Pfizer Global Manufacturing, Franklin, Ohio
Break flange for non-hazardous fluid
Michael Hartzes, senior process engineer
CDI Engineering Group Inc., Houston, Texas
Lock Out/Tag Out
Rob K. Riley, senior reliability rngineer
Air Liquide America LP, Geismar, La.
Depressure line safely
After the pipeline has been isolated, the section should be blown down using a controlled process, preferably a small isolation valve. If a valve for control is not available, flange bolts should be loosened to allow the gas pressure in the pipe to escape safely. If the pipe is too large or long to allow timely depressurization of the line safely, an adequately sized valve should be installed onto the piping and tapped to allow safe depressurization of the pipeline. Safety is paramount in depressurizing any pipeline and should be performed efficiently before any consideration of time and money.
After the piping work has been repaired and put back into service using a documented repressurization process, all documentation should be signed and dated by the workers. The signed document should be submitted, reviewed and filed for further reference.
Karl Watson, P.E., C.E.M., C.E.P., sr. engineer
Abbott Laboratories, Abbott Park, Ill.
Since there is no mention of any label or signage on the pipes and valves, color-coding with a unique ID would be the logical and least expensive first choice. You could actually use colored tape and apply a strip along the entire length of the pipe. Then, of course, a proper LOTO procedure that incorporates a second check by another qualified tag signer should be used. Another more expensive, and maybe less effective, option would be to relocate the "extra" pipe so that "three from the end" in the center of the room is actually "three from the end" on the wall.
Thomas Hinckley, senior process engineer
Texas Polymer Services Inc., Orange, Texas
Diane Dierking is senior editor for Chemical Processing magazine. E-mail her at email@example.com.