One of my blog posts that frequently gets picked up in web searches dealt with an accidental anhydrous ammonia leak in July of 2009 at Tanner Industries in Swansea, SC. So it was with a great deal of interest that I read this morning that the National Transportation Safety Board (NTSB) had determined the cause of the catastrophic hose failure that was the point of release in this fatal accident; the use of a hose that was incompatible with the anhydrous ammonia that was being offloaded.
It seems that someone (apparently from the trucking company, but that hasn’t been conclusively established) switched hoses between two trucks in a company yard. The hose that ended up on the truck at Tanner Industries that fateful day was clearly marked as being a hose to be used for transferring liquid petroleum gas (LPG). Internal components of that hose would be expected to react with anhydrous ammonia in such a way as to weaken the structural integrity of the hose.
The NTSB has issued a formal recommendation that the Federal Motor Carrier Safety Administration (FMCSA) and the Pipeline and Hazardous Material Safety Administration (PHMSA) should jointly issue a safety advisory concerning the necessity for checking hoses to ensure that they are compatible with the material being transferred to or from transportation tanks.
A separate recommendation letter also recommends that PHMSA:
• Require carriers and transfer facilities verify the chemical compatibility of hoses;
• Amend 49 CFR 173.315(n)(2) to require the use of passive emergency shutdown systems;
• Publish a formal interpretation of the when a transfer hose assembly is ‘in service’; and
• Clarify the testing and recordkeeping requirements of 49 CFR 180.407 for annual hose leak testing.
Long time readers might remember that I recommended the use of passive emergency shutdown systems in my original post on this accident. No great insight on my part, both the NTSB and the Chemical Safety Board had made this recommendation before.
As with most safety incidents, the root cause of this incident can point out security vulnerabilities in our chemical transportation systems. While the switching of hoses in this particular incident was not traced to terrorism, a terrorist could use this technique for attacking a high-risk chemical facility. Switching hoses as was done in this case could be done at any number of rest-stops, tank wash stations, or anywhere else where trucks are parked unattended. While it would be hard to predict when the hose would fail (NTSB estimates this hose may have been used as many as 12 times before the accident), this would be an effective form of attack where a terrorist wanted to attack multiple facilities over a wide area and reduce the chances of getting caught.
Another variation on this ‘hose attack’ theme would be to add relatively small amounts of an incompatible chemical to the inside of the hose. The material would then be flushed into the storage tank during the unloading process creating a chemical reaction hazard within the tank. This would be most effective if a chemical initiator were added to a self-reactive chemical storage tank.
Both of these types of attacks would be relatively easy to pull off because the hose storage racks on most tank trucks are not secured; many are not even covered.
Risk assessments by shippers, carriers, and chemical receivers should look at this issue and take appropriate safety/security measures to eliminate this as a readily available attack mode.