The timeline will be the basis for your root cause analysis (RCA). Before drawing it, develop a spreadsheet with all the relevant facts: who, what and when as well as supporting information. Having people recount what and when they did something isn’t enough — you’ll need proof. What do other shifts say? Distributed control system logs will show when equipment was started and stopped. Make sure you secure records on paper immediately after the accident. It’s probably a good idea to augment your spreadsheet with a “gotcha” table. This sheet will list items that OSHA will question or fine you on ― keep it honest but remember it’s part of the record. Look into past fines if you’re not sure what causes trouble.
Next, check the background information. Are your drawings, especially your process and instrumentation drawings, current and accurate? If they’re not, OSHA will fine you. Inaccurate drawings should be in your gotcha file.
With boxes of information collected, it’s time to put it all together. Now, you’ll start beefing up the RCA tree.
Because of the critical nature of this type of study you’ll want to keep track of your questions and other questions from the gotcha table. If possible, review the questions for clarity with others, especially non-engineers. After a few drafts, you’ll have a useful document.
As for how the operators died, I would avoid speculation. However, this accident sounds similar to how the fire started in Texas City in March 2005. It may be that the truck exhaust started the fire. Or, it may be that a loose stone sparked the fire; tank farms normally are filled with gravel rather than paved. This situation involving vehicles has happened before and OSHA and CSB have warned against it. Gee, maybe this is a gotcha? Operators now are taught to shift to park and run if they can’t turn off the truck ignition. That’s probably what saved the operators at Texas City. Clearly they were properly trained. Chances are that there won’t be definitive evidence of what killed the operators, so don’t waste time on it. You’ve got to prepare for the onslaught of reporters, company lawyers and other non-technical people who want to get the scoop on the accident.
Now, as for improvements, take careful stock of calibration records for alarms and level measurements in the tank farm. Review these with operators and managers separately; some safety measures don’t work the way they should. At this point, you’ll want to make a decision based on what you find out: take the offensive because you installed a perfectly good, well-maintained system that failed for some unexpected reason, or go on the defensive and promise to make amends. Make sure recommended improvements are thoroughly defined.
As always, keep good records, avoid jargon, and prepare a report almost anyone can understand. You don’t want your career to become another casualty of the accident.
Dirk Willard, senior process engineer
Swenson Technologies, Monee, Ill.
We feed grain via a screw conveyor from a silo to a mill. After grinding the material is conveyed by a pressurized pneumatic conveyor up six stories to cereal cookers. The pneumatic lines are bare pipe and run indoors. The mill room has fans but the air is humid in central Ohio in the summertime. Eventually, cereal is rolled into breakfast flakes. Unfortunately, the cereal often takes on a musty smell, which is worse in the winter. The cookers sometimes fail bacteria screening — the contamination has been traced back to the mill. Operators have seen water dripping from the conveyor ducts, although the moisture levels in the silo are only in the 8%–9% range. What’s the source of the mysterious water and how can we eliminate or reduce the odor problem? How would you approach this problem?
Send us your comments, suggestions or solutions for this question by September 12, 2009. We’ll include as many of them as possible in the October 2009 issue and all on ChemicalProcessing.com. Send visuals — a sketch is fine. E-mail us at mailto:ProcessPuzzler@putman.net or mail to Process Puzzler, Chemical Processing, 555 W. Pierce Road, 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.