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Each label is REQUIRED to include the following components:

  • Abbreviation for ammonia system components
  • The physical state – either liquid, vapor, or both
  • The marker body containing the word “ammonia”
  • The pressure level – high or low
  • The flow direction


Many thanks to Steve Stephenson

OSHA’s PSM standard requires Operating Procedures to address “special or unique hazards”

1910.119(f)(1)(iii) Safety and health considerations:

1910.119(f)(1)(iii)(E) Any special or unique hazards.

This item is often not necessary with many of the PSM standard’s Highly Hazardous Chemicals; however, HFO-1234yf has a unique property that falls into this requirement.  HFO-1234yf is…

Cases of Stress Corrosion Cracking (SCC) in steel vessels using NH3 have been reported by members of the ammonia refrigeration industry. When NH3 is used as a refrigerant, it is kept at -33° C (-28° F). While it was once believed that NH3 SCC)could not occur at such low temperatures, both practical experience and experimental studies have shown otherwise. The Industrial Refrigeration Consortium (IRC) has developed classes and issued technical bulletins for its members to address the causes and prevention of NH3 SCC.

The IRC has identified non-stress-relieved (non-annealed) welds and areas exposed to condensing NH3 vapor as “hot spots” for SCC. In one incident, a SCC attack formed a hole through a high-pressure receiver line from an NH3 refrigeration system. The hole initiated on the inside of the vessel and grew completely through the weld and heat-affected zones to the exterior surface. After the leak occurred, the interior surface of that pressure vessel was examined with a liquid penetrant, and this showed that several SCC 5 to 10 cm long cracks were present, all oriented perpendicular to the weld line.

Other cases of failure have been reported by the International Institute of Ammonia Refrigeration:

As I have written earlier, the new refrigerant HFO-1234yf is a Category 1 Flammable Gas.  This flammable gas is stored under pressure as a liquid, which by definition makes this material a candidate for a BLEVE risk assessment.  For those that are not familiar with the acronym BLEVE, it stands for Boiling Liquid Expanding Vapor Explosion and this week's "Video of the Week" is a Transport Canada training video on BLEVEs.  This type of vessel failure takes the term "catastrophic failure" to new heights and in a some-what famous BLEVE incident a LPG railcar traveled over 3,500 feet after it BLEVE'ed.  BLEVEs are indeed an event that is considered to be a "Low Frequency - High Severity" and thus often times are over looked as a plausible scenario.  I have been sorely disappointed in some of the responses clients and I have received from so called "reliable sources" (not so much any more in my eyes).  One such response was "this refrigerant is a mildly flammable material and carries no risks for a bleve".  Really?  You can call this Category 1 Flammable Gas a "mildly flammable" all day long, as that has ZERO, zilch, NADA, zip to do with estimating BLEVE risks!!!  In fact, the most recent BLEVE that resulted in three fatalities was a Carbon Dioxide (CO2) Tank in Germany and if you were not aware - CO2 is NOT a flammable gas - and in fact it is used as an EXTINGUISHING agent around the world.  So if HFO-1234yf is a BLEVE risk, what does this mean to those facilities who store HFO-1234 in ASME pressure vessels?  I will cover that answer in Part 5.

Screen Shot 2015 08 15 at 3.02.44 PMWhile doing some a BLEVE risk assessment I came across this 2007 research paper that I thought was an incredible read.  If you are one who works with BLEVE risk this is a MUST READ; if your someone who finds BLEVEs interesting and want to learn the inner workings of a BLEVE, this paper breaks it down and challenges each failure mode (hot vs. cold BLEVE).  During a BLEVE there is a LOT happening inside the vessel and EACH factor plays into the timing and severity of the BLEVE; this paper makes sense of these factors and really does a nice job breaking it all down.

CLICK HERE (pdf) for the paper in English

Cal/OSHA today issued 19 citations to a refinery for workplace safety and health violations following an investigation into the February explosion at the company’s Torrance refinery that injured four workers. The proposed penalties total $566,600.  Eighteen of the citations were classified as serious due to a realistic possibility of worker death or serious injury. Six of these serious violations were also classified as willful because Cal/OSHA found that the refinery did not take action to eliminate known hazardous conditions at the refinery and intentionally failed to comply with state safety standards.  The blast on February 18 was the result of a hydrocarbon release from the refinery’s fluid catalytic cracker (FCC) unit into its electrostatic precipitator (ESP).  The hydrocarbons ignited inside the ESP, causing the unit to explode. Eight workers were decontaminated after the incident, and four were sent to hospitals for treatment of minor injuries. Cal/OSHA’s investigation concluded the following:

  • A 2007 safety review uncovered concerns about flammable vapor leakage in the ESP. Management knew of potential fire or explosion hazards as a result of the leakage, and failed to correct the danger.
  • An incident response team, which included refinery senior management, was aware of a leaking spent slide valve on the FCC unit before the accident occurred.
  • The FCC unit had not been working properly for as many as nine years prior to the incident. There was no functional pressure transmitter and as a result, the refinery was unable to monitor hydrocarbon pressure buildup in the unit.
  • There was no written operating procedure for placing the FCC unit in hot standby, which is a state between startup and shutdown that can be compared to working on an idling car.

Cal/OSHA issued an order prohibiting use of the FCC unit on February 18, and that order remains in effect until the refinery can demonstrate that the unit is safe to operate.  Here is a breakdown of the citations:

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