There are lots of questions still unanswered about the leak of toxic ammonia gas that went undetected for nearly two weeks at Dow Chemical’s Institute plant (shown above in a company photo).
What kind of monitoring system does Dow have in place in that part of the plant? Were the monitors working properly? Were they calibrated to specifically detect ammonia and, if so, at what amounts?
We’ll have to wait a while longer for answers to those questions. Local Dow officials aren’t allowed to talk to the media in the communities where the company operates, and Randy Fischback, a corporate Dow spokesman flat-out refused to return my calls or give me a phone interview.
Apparently, Dow is going to require all questions about this incident to be submitted in writing, and will only answer those questions in writing. I’ve sent them a list of questions, but haven’t gotten word on when they might be answered.
In the meantime, I thought I would pass on this prepared statement that Dow issued today:
At approximately 1:30pm EST on Wednesday, February 17, 2010, Dow discovered an anhydrous ammonia leak coming from a pressure relief device on a storage tank at the Institute Facility. The leak appears to have exceeded the Reportable Quantity from around February 4 to February 17. At its peak, the release rate was approximately 11 pounds per hour. Air dispersion modeling confirms that at this leak rate no adverse health effects would be expected, either onsite or offsite. Upon detection, the leak was stopped within 30 minutes.
There were no offsite odor complaints during this timeframe, nor was the odor strong enough to be detected by plant workers on their twice-daily rounds. Notably, the maintenance technician who found the leak could not smell ammonia even when he was standing next to the leaking valve, and only discovered the leak through the use of a portable leak detection meter. Had this been a larger release, our fixed ammonia detectors, four of which are located in close proximity to the tank, would have alerted us to a problem. Both the pressure relief device and the ammonia detectors are routinely inspected and tested.
Humans can detect the odor of ammonia well below the level at which it is irritating, and even further below the level at which it can cause significant health effects. Most people detect ammonia in concentrations at 5 ppm or lower. Ammonia is irritating to eyes, nose, and throat in concentrations around 70 ppm. OSHA has set a safety limit of 50 ppm as a safe average concentration for an 8-hour workday. Because the concentration was so low as not to be detected, we are confident that there was no risk to employees or public at any time. To put it in perspective, a person using ammonia cleaners would be exposed to concentrations greater than were present here.
An incident review will be conducted to determine the cause of the leak and appropriate measures to prevent reoccurrence.
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The company’s release stated: “At its peak, the release rate was approximately 11 pounds per hour”. ….. How does that relate to the ppm irritation limit of ~70ppm? – or the safety limits of 50 ppm/8 hour day? ….
Or at least, what was the ppm at the time the leak was discovered — or the 30 minutes it tok to shut it down ? — or any of the time during the several day period the release continued ?
— Just curious.
Good question, Cindy … I’m going to go ahead and paste here some additional information Dow provided to me today. I’m still trying to get some of my questions answered … here’s what they said so far:
The storage tank is a pressure vessel located about 400 yards east of the Catalyst process, and holds ammonia that is fed as a vapor into an emissions reduction system. The tank has an established maximum fill level of approximately 40,000 pounds. When the leak began, the tank was about half-full, or approximately 20,000 pounds. The pressure relief device is at about 20 feet in elevation.
As part of our commitment to safety for the communities in which we work and live, UCC had installed four ammonia gas detectors. Two are located at the tank, and two are located about 30 yards away at the unloading rack. These detectors are specifically designed to detect ammonia. They passed their most recent quarterly calibration test in January 2010. These detectors are intended to give warning of large releases that could pose an immediate danger. They were not designed to catch gradual leakage in the range of ounces per minute from a relief valve. The release also did not produce concentrations that were smelled during plant rounds. There were no odor complaints from workers inside the plant or from members of the community outside the plant associated with this release.
There are media reports about an odor complaint during this time, however Bayer CropScience had determined, based on the description of the odor, that those complaints did not result from the operations at any Dow manufacturing facilities in Institute. Metro 911 has also confirmed that they did not receive any related odor complaints during this period.
The tank does have instrumentation to show the level of ammonia in the tank. Minor fluctuations in the tank level are normal, and can occur due to daily or seasonal temperature changes, as well as the amount of ammonia demand from the emission control system. Operators discovered an unusual level indication with the ammonia inventory, even accounting for the factors noted previously. Although there was no knowledge of a leak at that time, the operators are trained to troubleshoot unusual situations – and so they took action to investigate. The initial investigation took place at ground level around the tank and found nothing that indicated a leak. Once no leak was identified, the level device was investigated. While awaiting results of that testing, plant personnel conducted additional testing for a potential leak, including using a manlift to inspect the top of the tank.
It is important to note that most people can smell ammonia at 5 parts per million, which is a non-harmful concentration that could be encountered with ordinary household cleaners. During the investigation of the level discrepancy, a portable detector with a sensitivity of 1 part per million was utilized, and it indicated that there was a leak from the pressure relief valve. We are investigating why ammonia was slowly leaking through the valve. The valve was tested in March 2009 and was working properly. The valve is set to open at 250 psig, and the tank operates only up to 130 psig during normal use. There had not been any over-pressure event that would have opened the valve.
Upon discovering the leak, our personnel took action to stop the leak and to notify appropriate authorities. ALOHA modeling was conducted, using the height of the pressure relief valve and the typical ambient meteorological conditions as inputs. We modeled a concentration of 25 parts per million. OSHA’s current Permissible Exposure Limit is 50 parts per million average exposure over an 8-hour working day for a full career, so the 25 part per million value is more conservative. Modeling indicated that no concentrations approaching 25 parts per million would have reached the perimeter fence.
Since the buck has been passed by our local government officials (Mr. Kent Carper etc….) to nominate Joe Q. @ and Jane Q. Public as the Watchdog Air Monitors over the Chemical Companies I sure do hope they know the proper procedures.
Our trusty local media has made sure of it right? If not here are the true facts folks. Should you smell any strange odors in the air first report it to 911 then report to the Dept.of Environmental Protection and Homeland Security at 1-800-642-3074 this is the 24-hour number. Please call ANYTIME you smell something!