We have had many discussions on SAFTENG regarding pressure vessel safety, but it is the Year 2020 and we need to have a very direct talk about how we manage flammable liquids and combustible materials around our pressure vessels. In this article, I am primarily speaking to those in the Anhydrous Ammonia fertilizer industry and more specifically to those who are using the Nitrogen Stabilizers. Since I posted the Canadian Safety Alert regarding these additives and their impact on the containers and valves, it has generated a lot of questions about how these N2 Stabilizers are stored and handled in relation to the storage tanks and nurse tanks. Bottom line… good practice, OSHA, and our RAGAGEPs all require that we keep the area(s) around our pressure vessels clear of anything that will burn; so when we have totes full of a Flammable Liquid (Cat 3 with a FP=104°F) stored in the shadow of a pressure vessel which contains a Cat 2 Flammable Gas (NH3) or a Cat 1 Flammable gas (LPG) stored as pressurized liquids we have violated every last ounce of fundamental safety regarding our pressure vessels.
Let’s discuss the Anhydrous Ammonia tanks and the specific concerns, requirements, and practices regarding these bulk pressure vessels.
FOLLOW-UP NOTE:
I was pleased to see that one of the flammable N2 stabilizers is maybe being phased out and replaced with a product that is NOT even combustible! Now I am not sure why this was done, but a rep from the company must be reading my stuff as he/she was very helpful in educating me about this next generation stabilizer and its safety benefits. This sure is a great thing for those who work with these stabilizers. Many of these businesses had no idea how to handle flammable liquids and the addition of these flammable liquids to these bulk ammonia businesses is just a risk we do not need!
First thing, imagine there is a force-field around your pressure vessels that extends 20′ all the way around and above your tank(s). Nothing can access this 20′ radius; this means that your loadout valve arrangements/headers are outside this 20′, but if the facility has been around a while I am betting that the truck unloading position will be closer than 20′, so we can make an exception for the truck positioning as long as we have more than adequate barrier protection.
But when it comes to this 20′ radius, we CONTROL EVERYTHING and EVERYONE entering and exiting the “force-field”. It is OFF LIMITS for general storage, and most certainly off-limits for storing other hazardous materials, especially flammable and/or combustible liquids. We do this in the spirit of PREVENTING, PROTECTING and the ability to MITIGATE any leaks that may occur. We will discuss the hazards of having these flammable and/or combustible liquids stored near by, but before we discuss that, think about how these totes/drums are moved… forklifts! The #1 enemy of these processes! NEVER should we allow powered-mobile equipment access to our pressure vessels. Allowing this on a daily basis is pure insanity from a simple “contact hazard”. But let’s say the totes/drums are stored outside of the vehicle protection barriers, but still in the shadow of the bulk tanks; the hazard then moves to a potential “pool fire” involving the bulk tanks or nurse tanks in the area. This is a SIGNIFICANT threat to these pressure vessels and the risks can be easily abated by implementing the 20′ rule. Where do I come up with the 20′ rule?
The 20′ rule comes out of OSHA’s LPG standard, 1910.110, and yes – I APPLY this requirement to ALL pressure vessels that are storing a Liquidfied Pressurized Gas, regardless if it is flammable or toxic. Here is what OSHA’s says about safe distances for LPG vessels: (emphasis by me)
1910.110(b)(6)(vii) The minimum separation between liquefied petroleum gas containers and flammable liquid tanks shall be 20 FEET, and the minimum separation between a container and the centerline of the dike shall be 10 feet. The foregoing provision shall not apply when LP-Gas containers of 125 gallons or less capacity are installed adjacent to Class III flammable liquid tanks of 275 gallons or less capacity.
Unfortunately, OSHA’s Anhydrous Ammonia, 1910.111, does not make any such statement, it only states:
1910.111(b)(5)(v) Storage areas shall be kept free of readily ignitable materials such as waste, weeds, and long dry grass.
So we got a lot of flack regarding our audit findings and PHA findings regarding the storage of these flammable liquids within 20′, as such there is NO OSHA requirement for this. Yes, people would try and make a case that having flammable liquids in the shadow of the tank was allowed, just not waste, weeds, and long dry grass. I will be the first to admit that waste, weeds, and long dry grass can be ignited much easier in ordinary settings vs. having to have a spill of the flammable liquids AND then ignite these liquids. But the reason why 1910.111 speaks to waste, weeds, and long dry grass and not to flammable liquids, is that in 1974 when the standard was issued it was done so using ANSI K61.1 and no one had any idea of Nitrogen Stabilizers at the time. About the only flammable liquid found at these businesses is maybe diesel fuel, but then it is usually in a smaller style tank and poses a lesser degree of a hazard to the pressure vessels – such there is no specific mention of flammable liquids in the standard, only waste, weeds, and long dry grass which is usually plentiful in these business locations. Our designs for these businesses call for gravel to cover the ground 20′ around these tanks and then we use weed kill to control the vegetation as I do not even want a push-mower in my 20′ radius.
If you have LPG/Propane tanks, then certainly 1910.110(b)(6)(vii), as shown above, will apply and we have a clear mandate to keep flammable liquids away by at least 20′. But 1910.110 offers even more structure on how we should manage our 20′ radius: (emphasis by me)
1910.110(b)(6)(vi) Readily ignitable material such as weeds and long dry grass shall be removed within 10 feet of any container.
1910.110(b)(6)(vii) The minimum separation between liquefied petroleum gas containers and flammable liquid tanks shall be 20 FEET, and the minimum separation between a container and the centerline of the dike shall be 10 feet. The foregoing provision shall not apply when LP-Gas containers of 125 gallons or less capacity are installed adjacent to Class III flammable liquid tanks of 275 gallons or less capacity.
1910.110(b)(6)(viii) Suitable means shall be taken to prevent the accumulation of flammable liquids under adjacent liquefied petroleum gas containers, such as by diking, diversion curbs, or grading.
1910.110(b)(6)(ix) When dikes are used with flammable liquid tanks, no liquefied petroleum gas containers shall be located within the diked area.