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.
Martin West, maintenance engineer
Sunoco Inc., Tulsa Refinery, Tulsa, Okla.

Labels require care

The type of labels/plates/etc., have to be considered. Some of our color coded labels had to be replaced after a very short period of time due to exposure to the chemicals.
Brad Stanley, chemical engineer
Purafil Inc., Doraville, Ga.

Loosen one bolt at a time

From the information provided, I believe that the line would have still been under pressure had the correct valve been blocked in. It appears that all the nuts/bolts holding the topworks were removed. It also appears that there are no bleed valves or other points in the line to verify that the line is not under pressure. It should be the policy for maintenance to never remove all the bolts, especially if the line might be under pressure. Our maintenance personnel are instructed to loosen the bolts, but not fully remove them, on the side of the valve that is not in the line-of-fire, or to crack open a flange in the line, if possible. If the line is under pressure, the material will be released through the small opening away from the personnel breaking into the pipe system. Sometimes this takes a little longer and you have to wiggle and fiddle with the sealing surfaces, but if there is pressure, the leak is small and can be stopped quickly by tightening the bolts/nuts on the side that is leaking. For rusted and corroded nuts and bolts, we will break and replace them one at a time prior to actual maintenance work. This ensures that the nuts and bolts will be easy to work if we develop an unplanned leak.