This week social media once again provided us an eye-opening video… flaring off an MC331 Tanker of anhydrous ammonia (NH3). In my days, I have flared off both tanker trucks and railcars, and even worked with flaring systems on refrigerated atmospheric bulk storage tanks of NH3 at large NH3 terminals and NH3 manufacturing plants. The fact that these flaring systems and practices have been around since the early 1970’s tells us that NH3 will indeed burn, but there is a catch, as well as the wrong way and right way to do this task. This article will discuss the hazards associated with flaring off NH3 and discuss the potential for the scenario in the video below to be a PSM/RMP covered process…
I am betting that what we are seeing in that video is an MC331 trailer that was being used to haul NH3 during the spring and summer months and now the owner wants it converted over to an LPG trailer so it can haul LPG during the winter months. This is VERY common at this time of the year and in February/March of next year, they will probably use the same flare to burn off LPG heels to convert the trailer back to NH3 for the spring crop season.
NOTE: I have been corrected – the trailer was being emptied for its internal inspection.
In order to empty the NH3 trailer, the “shop” will “flare off” the contents rather than release the NH3 to the atmosphere and create a hazard and potentially have a “reportable release” (RQ for NH3 is 100 pounds over a 24-hour period).
The way this works is that Anhydrous Ammonia (NH3) will burn, but it is not done easily, so we use a “fuel” like Natural Gas or Propane to help it along. The fuel is like a “pilot light” and this pilot burns in excess of 1,200°F (ignition temp for NH3 gas). This means that the flare can achieve a 99% (or higher) destruction of the NH3 gas as long as it is operated properly!
As can be seen and heard in the video above, the flaring is working… by the way, if you smell NH3 during flaring YOURE DOING IT WRONG! Because NH3 has such a low odor threshold this is indeed an easy means to identify your NH3 pressure is too high or your pilot fuel is not reaching the necessary temps, but we should not smell ammonia in a set up like the one shown above. It may be different on a damaged trailer, but then again you would not have the flare that close to an UNCONTROLLED RELEASE of NH3.
A couple of items to discuss from the video:
1) The LPG containers are too close to the flare discharge. At the :21 second mark into the video we can see the “Shop Propane” cylinders about 15-20′ away from the flare. WAY TOO CLOSE for my liking. I like to have my cylinders behind a fire barrier (jersey barriers work well) and around 50′ away; without a suitable barrier I increase my distance by 25′ to 75′. Yes, this increases the length of hose needed, but this is a SHORT DURATION task and in a HIGHLY CONTROLLED ENVIRONMENT so the length of hose does not pose a significant risk increase.
2) The LPG containers are IMPROPERLY labeled. At least meet 1910.1200(f)(6) requirements! The wording “Shop Propane” is a nice start, but not quite compliant.
3) The clearance around the flare is not large enough nor far enough from the MC331 PRESSURIZED VESSEL. I understand this is a MC331 that has not been compromised and is most likely in good condition, but just how close should we have an open flame that is 6-8′ in height and burning at over 1,200°F to this container? 50′? 75′? There is NO code or standard on flaring off these containers, but a general rule of thumb is to ask… “What if the flare is pulled over and lands pointing at my container?” Newer emergency flare systems will have a fuel hook up that has a level sensor in it and if it is tripped it closes the fuel valve and stops the flaring; however, I have only seen this in the latest design and it is certainly not in the design of the system in the video. If we look closely we see the flare feed hose is wrapped several times around a device before reaching the flare, indicating the flare is capable of being positioned further away than it was in the video.
4) this set up is tying in the propane into the NH3 hose! – We know that these two hose materials are NOT compatible with these materials, so having the propane mix with the NH3 in a single hose begs to question… what the heck is the material of construction of this super hose?!?!? SAFTENG Members can see my post regarding the NTSB Alert regarding the importance of making sure NH3 hoses are used for NH3 and LPG hoses are used for LPG and the disastrous effects of when these hoses are mixed up!
and the big question/concern
5) this could be a PSM/RMP covered process! These MC331 NH3 tankers will hold, when safely full, 40,000 pounds (i.e. 20 tons) of NH3. This means that if the truck shown in the video was just 1/4 full we have ourselves a PSM/RMP covered process. Both OSHA and EPA (as well as DHS CFATS as of this year) all state that a trailer WITHOUT its motive power (e.g. dropped trailer) and this trailer has more than the PSM/RMP threshold for its HHC/EHS then the sole trailer sitting there would in fact be a “covered process”. What does this mean to the “flaring operation” being conducted:
- Process Safety Information is needed on the design of the flaring system. What is the pilot fuel, what is the flow rate/pressure of the pilot fuel to achieve the desired destruction rate of the NH3, etc. How much fuel is needed based on how much NH3 is present to burn (e.g. Material and energy balance)? Hose materials of construction? SDS for both LPG and NH3. In other words, a full set of PSI for this process is needed and may I suggest that even when the process is less than 10,000 pounds we should take this approach.
- Process Hazards Analysis – big one here is “facility siting” of the flaring system. How close can it be to a property line, “important building”, etc? How far does it need to be away from the MC331 container? Doing a PHA like a what-if analysis and asking questions like “what if we run out of fuel”, “what is we do not meet the 1200F temp at the flare”.
- Operating Procedures are a MUST for both set up, operation and break-down. The procedures need to specify PPE needed to work around flaring systems that are using flammable gases. We need to establish the safe upper and lower operating limits for the NH3 and pilot gas, consequences of deviating from those limits and the steps to correct/avoid those deviations. We need to have an emergency shutdown procedure or an engineered shutdown system that includes the condition in which to activate the ESD.
And the list goes all the way through the other 11 elements and don’t forget that NH3 is also an RMP chemical and we would need to have our RMP’s OCAs in place and everything submitted BEFORE we accept a trailer that is 1/4 full (e.g. 10,000 pounds).