Process Puzzler: Keep cables in their place

(Editor's Note: There is a figure that accompanies this article that can be downloaded in PDF format via the "Download Now" button at the bottom of the page.)

QUESTION FROM NOVEMBER’S CHEMICAL PROCESSING

An electric cable bundle was supported by cable hangers. The hooks at the ends of the cable hangers were hooked over the top of a metal strip (see top figure). The electric cables had to be lowered to the ground to provide access to whatever lay behind them. When the cables were returned to their supports, they were put back as shown in the lower part of the figure. This increased the load on the upper hooks. One hook eventually failed, increasing the load on the adjacent hooks. They then failed. A 200-ft. (60 m) length of cables fell, injuring one man. How can we avoid this situation in the future?

Use stronger cable hangers
Many people would fail to see this hazard, so I would recommend reiterating the correct method through instruction and improved training.However, since many years might pass before the job has to be done again, training is unlikely to be effective in the long term. The best solution is to use cable hangers that are strong enough to carry the weight, even if they are used in the wrong way.Trevor Kletz, safety consultant
Cheadle, England

Add a collar
Add a bracket or collar around the hooks so the only way to install them is the correct way.
David W. Fry, project engineer
CP Kelco, San Diego

Design a foolproof system
I would affix hooks to the metal strip and then use cable hangers with eyelets that attach to the hooks. This would prevent the situation encountered with hooks on the end of the cable hangers. However, you would have to design the arrangement to prevent more than one end of the cable from being connected to the same hook.

Another option would be to design a male-female coupling connection. This would ensure that the cable hangers would be used properly.
Randy Turk, site manager
Engelhard, Elyria, Ohio

Upgrade the hangers
Training can reduce the likelihood of a recurrence, but there is always a chance that someone won’t get the message. The surefire solution is to upgrade to a larger-gauge cable hanger so that, even if installed incorrectly, one hook will be able to support the entire load. This has the added benefit of being able to prevent another chain reaction if a single support fails in the future.
Gary Wise, senior engineer
Ecology & Environment Inc., Tallahassee, Fla.

Use a cable tray
Hangers are best used only as temporary cable supports. A cable tray provides a safe and practical method of support, and they are available in many sizes and materials.
Kent McKean, senior automation technologist
UMA Engineering Ltd., Winnipeg, Manitoba

Distribute the load
Make a clamp that fits over the top of the metal strip and into which each of the weight-bearing hangers fits. The clamp should allow only one hanger hook to fit in the hole on one side of the clamp and the other hook on the other side of the clamp. It will be obvious to whoever is replacing the hangers that there should be a hook attached to each side. This arrangement would better support the weight of the cables than in the “correct” figure, where the hooks are attached at the same place.
Michael Fantuzzi, formulation chemist
Soft Gel Technologies Inc., Los Angeles

MARCH’S PUZZLER

We make adhesives by batch processing solvents and about 1,500 lbs of solids in 3,000-gal. tanks. Our base solvents are hexane, acetone and isohexane. The formula calls for a three-hour mix cycle on high speed to dissolve the solids -- at this time we lose about 15% of the solvent volume. Although the tanks have fixed lids, they are not pressure vessels. Is there a way to reduce the solvent losses by altering our mixing procedure or tank configuration? Is there any other way? Send us your comments, suggestions or solutions for this question by Feb. 5. We’ll include as many of them as possible in the February 2005 issue. Send visuals, too — a sketch is fine. E-mail us at [email protected] or mail to ProcessPuzzler, Chemical Processing, 555 W. Pierce Rd., Suite 301, Itasca, IL 60143. Fax: (630) 467-1120. Please include your name, title, location and company affiliation in the response. And, of course, if you have a process problem you’d like to pose to our readers, send it along and we’ll be pleased to consider it for publication.