What’s in Print

Clearing up questions about pressure-relief vents on 300 Series cargo tanks

THE last 300 Series tank rolled off the assembly line over 20 years ago, and yet there still is discussion out there as to the correct way to upgrade pressure-relief venting on those tanks.

Glen Harm, director of engineering at Girard Equipment, said during the 2017 Tank Truck Week in New Orleans, Louisiana, that there is new information—two incidents that happened last year—that is very important and backs up what the Truck Trailer Manufacturers Association (TTMA) has written in the past about DOT400 Series cargo tank vents on MC300 Series cargo tank motor vehicles (CTMVs).

On May 16, 2017, James Bromm, an inspector for the Federal Motor Carrier Safety Administration’s (FMCSA) Illinois division, issued a violation to LT Harnett Trucking Inc for a tank that was built in July 1988 by Polar Tank Trailer. It was an MC307 tank with a design pressure of 30 psig. At the time of the inspection, it was equipped with a Girard DOT407 MAWP 30 psi pressure vent, which was set to discharge at 36 psi.

The violation was written this way: “MC307 venting; MC307 (30 psig MAWP) equipped with MC407 vent with a set pressure of 36 psig (MAWP).”

“Well, it wasn’t an MC407 vent,” Harm said. “It was a DOT407 vent.

“The issue the inspector was bringing up was that it was a wrong pressure at 36. There are still thousands of MC307s out on the road. Maybe your company will end up being pulled over and a violation written. We want you to know exactly the steps that were taken to have this violation removed.” 

Harm showed a photo of the data plate, which said that it was manufactured in 1988, and the designed pressure was 30 psi.

“In the old MC rules, that meant that it should set to discharge at a designed pressure and up to 110% over the designed pressure. That means that the set-to-discharge should have been 30 psi to 33 psi.

“This tank was taken out of service. That meant LT Harnett was not making any money because it had to be taken out of service until this was fully resolved. This is what we want to try to avoid.” 

He said an inspection had been done a few months before the violation was cited. He showed a page of the registered inspection report for that tank that said the set-to-discharge was 36. 

“So this is what the federal motor carrier inspector saw,” Harm said. “He saw that the set-to-discharge was 36 and felt that was incorrect. I worked with LT Harnett and some other people on TTMA. We wrote an explanation for this violation. LT Harnett went on to DATAQ and they filed an explanation. It’s a simple explanation. It just says that 178.347-4 allows this to happen, that you can upgrade an MC307 tank trailer. We took that right out of the code of regulations and put that in there.” 

Last July, the violation was removed. 

“This is the first time, to my knowledge, that anyone has ever received a violation for putting a DOT407 pressure vent on a 300 Series tank,” Harm said. “People said it happened. I did some investigation and this is first time it ever happened, and we’re happy to see that a few months later, the violation was removed. So if anyone has issues with MC307s on the road and they put a DOT407 vent on the tank, as long as it meets the full requirements in SCFM, for that square footage for the tank, they are good.

“LT Harnett has returned the CTMV back into service. They didn’t change the vent or do anything. They are allowed to keep using that pressure vent on the cargo tank.”

The second incident happened on September 5, 2017, when the Pipeline and Hazardous Materials Safety Administration (PHMSA) released a letter of interpretation regarding a request (Reference #16-0183) by Daniel Shelton, president of HazMat Resources Inc.

“Shelton wrote this scenario of, ‘Can you put a 407 vent on a 300 Series tank?’ ” Harm said. “Good question. A lot of people have asked that, and there’s a lot of confusion out there. Can this really be done? In answer to his request for an interpretation, we got a good response back from PHMSA. We’re very happy with the response. To us, it clears this question up completely. Can I put a 407 vent on a 300 Series tank? The answer is yes. 

“It’s perfectly legal to put it on as long as the total flow rate meets what’s required by the regulation. You want to make sure you meet the required flow rate in SCFM for that cargo tank. That’s the most important thing. 

“We feel very strongly that this has finally been put to rest. Now, it isn’t mandatory for people to upgrade. If you have 307s out there on the road and have a 307 pressure vent on that and feel comfortable—and there are a lot of people that have been running these trailers for 30, 40 years and are perfectly happy using a 307 vent—you don’t have to upgrade. But it’s your choice. You can if you want to. We feel this letter of interpretation fully backs up what TTMA has written in the past and their stance on upgrades.”    

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