Piping Layout Nearly Causes a Fatality

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
Cheadle, England

Perform a HAZOP
The HAZOP review methodology would have caught this situation. Key deviation "Operator Interface."
Tim Goebel, senior staff engineer
CITGO Petroleum Corp., Lake Charles, La.

Label the lines
Label or otherwise differentiate the lines; paint each line a separate color or color the odd line on the right differently, which is not part of the system. Additionally, stencil the name/contents of the line or where it goes on both sides, or, if they all contain the same material and are part of the same system, clearly mark them with letters on both sides.
Dawn Morris, process engineer
GB Biosciences, Houston, Texas

Operator training
The most logical and inexpensive way to fix the problem is to label and color code the pipes and to conduct better operator training. I see no need to do a major design overhaul. Both the operator and the mechanic should have traced the line and checked the valves to ensure proper lockout/tag out (LOTO); with good labeling and color coding of the pipes, the accident could have been easily prevented.
Robert Inouye, lead operator
Tessenderlo Kerley Inc., Burley, Idaho

Danger of expanding liquid
There is a serious issue presented with the layout as shown in the sketch. If there are block valves at both ends of a pipe, there exists the real possibility of blocking a line in at both ends and then blowing it apart if the process fluid expands due to changes in temperature. We experienced just this situation about 20 years ago when we blocked in an aqueous ammonia line coming from outside where the temperature was about 30 Degrees F. As the cold liquid warmed up, it built so much pressure that it literally blew a cast check valve apart, spraying one of our operators with aqueous ammonia.
Mike Moore, corporate engineering manager
Mapei Corp., Deerfield Beach, Fla.

Label with line numbers
All three valves in each line should have some form of identification attached or engraved on them depending on the valve size. P&IDs show line numbers; the line number should be included in the tag or valve identification. Then the operator only needs to check that the line numbers are the same before closing the isolation valves.
Terry V. Molloy, P.E., president
CMES Inc., Novato, Calif.

Key lock mechanism
Use a key lock mechanism with a matched pair of valves so that the key for closing the second valve is only available after closing the first valve.
Swami R. Swaminathan, principal instrumentation engineer
Technip USA, Claremont, Calif.

Add a check valve
A one-way check valve should be added to the system. The presence of a one-way check would have prevented a continuous release of pressure back to the fine adjustment valve; however, this would not have prevented a short burst of pressure.
Kirt Matson, formulation plant manager
Van Diest Supply Co., McCook, Neb.

Label lines
The simple solution to this problem is to label the lines. Not knowing a line destination or service is typical in older plants. I was once in the utilities area of a chemical plant and we experienced several problems like this. Our solution was to verify the purpose of each line and its destination and to label it as such. This reduced the amount of mishaps by 90%. Also, a drawing showing all lines and services should be reviewed prior to any issuance of a work permit.