A few months ago I wrote about this new refrigerant as having the catastrophic risk of a BLEVE event. Now I wish to offer some guidance on how a business utilizing this refrigerant can reduce the likelihood of this type of event. First, there are NO engineering standards that guide a manufacturer of an ASME pressure vessel in how to construct a pressure vessel so that it will not fail in a BLEVE event. So we can not assume that our vessel is so well designed or constructed that it will with withstand either a hot or cold BLEVE. Our FIRST LINE of defense in managing BLEVE risk(s) is the placement of our pressure vessel(s). If our facility is in a state with an adopted fire/HAZMAT code(s) we will find some baseline “facility siting” instructions in these state-adopted codes. But this new refrigerant has no specific code(s) to aid a business in how they should manage their “facility siting”. However, there are some codes and RAGAGEPs designed for other Category 1 Flammable Gases (which HFO-1234yf is) and it is these codes and RAGAGEPs I turn to when asked about tank location.
HFO-1234yf is stored as a Liquified Pressurized Gas (LPG) – NOT to be confused with Liquified Petroleum Gas (LPG). This state makes it a candidate for a BLEVE event. Now HFO is NOT the same chemical a Propane (LPG), but they are in the same Hazard Category (e.g. Category 1 Flammable Gas) so it seems fitting that we could certainly apply the same layers of protection we use for Propane (LPG) to our HFO process. In fact, many of the pressure vessel being built to store HFO are being built to the same criteria as LPG storage tanks – making the connection to 1910.110 and NFPA 58 even stronger as it applies to storage tank “safety”.
HFO-1234yf storage tanks should NOT be placed inside secondary containment basin (e.g. dikes) that also house Category 2 and 3 flammable liquids.
PLEASE NOTE: from a PSM “process” definition, it would not be a stretch for OSHA to say that those Cat 2 and 3 flammable liquid tanks can impact the HFO covered process and thus consider all the tanks within the shared secondary containment as a “single process” due to “co-location”.
But the main reason we do NOT want our HFO-1234yf storage tank inside a shared secondary containment system is the risk of a “pool fire”. Yes it is true for a “pool fire” to happen we would have to have multiple failures occur – but what accident doesn’t have multiple failures before the end result? Process Safety is ALL ABOUT managing even those events that may have a low probability, but have a HIGH SEVERITY consequence. Both NFPA 58 and 1910.110, require that a propane (LPG) storage vessel be placed such that NO FLAMMABLE liquids can get within 20’ of the storage tank – a VERY good practice to apply to our HFO storage tank. The reason why both NFPA and OSHA have this requirement in their standards is to prevent the propane (LPG) storage tank from being involved in a pool fire.
OSHA LPG Standard
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.
NFPA 58, 2014
6.4.4.4* The area under containers shall be graded or shall have dikes or curbs installed so that the flow or accumulation of flammable liquids with flash points below 200°F (93.4°C) is prevented.
6.4.4.5 LP-Gas containers shall be located at least 10 ft (3 m) from the centerline of the wall of diked areas containing flammable or combustible liquids.
6.4.4.6 The minimum horizontal separation between aboveground LP-Gas containers and aboveground tanks containing liquids having flash points below 200°F (93.4°C) shall be 20 ft (6 m).
Again, I am aware that HFO-1234yf is NOT the same material as Liquified Petroleum Gas (LPG), but since we do not have any codes/standards specific to HFO-1234yf we have to use our best judgment. Both LPG and HFO are Category 1 Flammable Gases so the uses of these codes/standards make perfect sense; especially if the design of our storage vessel was the same used for LPG vessels.
Relief Valves prevent BLEVEs
FALSE! Relief valves help limit the impact of a BLEVE, but they are the devices that take us down the path to a BLEVE. Of course not having relief valves on a pressure vessel is a MUCH WORSE alternative, but RV’s do NOT prevent a pressure vessel from a BLEVE event. In fact, almost all BLEVEs have occurred on vessels equipped with RVs.
Bottom line…
We should NEVER place a pressure vessel storing a liquefied pressurized gas in a shared secondary containment basin with other flammable liquids. We should strive to place these tanks as far away from important buildings, all ordinary combustibles, and combustible and flammable liquids. I like to say, we pay attention to even the landscaping (mulch, grass, shrubs, and trees) around our pressure vessels. One we should not permit any combustibles is placed around our vessel and two we should not have anything that would require anyone to run a lawnmower or weedeater around our Category 1 Flammable Gas vessels on a regular basis. By all means, these workers using non-rated equipment should be working under a Hot Work permit if they are doing work within the HAZLOC around our vessel.
Until we have an HFO-1234yf code/practice that is specific to the hazards of HFO-1234yf, we are forced to use other RAGAGEPs that make sense. Our state Fire/HAZMAT codes and NFPA 58 are an EXCELLENT starting point for consideration and will certainly provide ample layers of protection for our bulk storage of our HFO-1234yf.