March 20, 2018
As defined by the AS 4343 standards, pressure equipment hazard levels do exist as a living document, one that's meant to clearly identify the risk factors that accompany this field of activity. By risks, we're referring to the immense pressures and volumes that shape this potentially dangerous industry. We deal in certainties and probabilities, in consequences and methods that annul these potential consequences. What are these levels?
Starting with Hazard Level A (high-risk equipment configurations), this concise list moves through levels B, C, D, and E:
Level A - Installed in oil refineries and chemical processing plants, these multi-ton containers store huge quantities of highly flammable fluid.
Level B - Think of the medium-to-high volume containment units that exist in large plant rooms. A room-sized boiler would fall under this category
Level C and D - Stepping down another rung on the hazard ladder, the pressure vessels tagged here are used in small equipment set-ups. An air compressor in a garage likely uses this safety designation
Level E - Extra-low pressure vessels mount this identifier. The vessels are probably spared special regulatory control, but they're still part of a general safety program
In short, every factor impacts the vessel design. However, there's a long-form answer, too. Documented in the AS4343:2014 guidelines, the mass, fluid type, and flammability rating of the subject fluid will immediately bias the hazard level. Dangers to human life and the environment also impact the risk factors, so a highly toxic fluid is likely to receive an A or B designation. After all, even if this pressurized chemical stuff isn't combustible, it could wipe out an entire community because of its toxicity level.
Engineering factors also influence the risk assessment program. Think of the fluid dynamics taking place inside the pressure vessel. Maybe the fluid isn't highly combustible at a lower pressure, but it has a lower flashpoint when it's exposed to more space-constraining force, so much so that it could "flash" and cause a catastrophic incident. Finally, what about the service conditions? Other vessels, an offshore setting, these and other external factors will impact the pressure equipment's hazard level.
There are parent design standards and children installation/commissioning standards that regulate every action. The AS 4343 guidelines descend from the parent manufacturing and fabrication directives, but they're every bit as important as those central precepts. All things considered, it's the pressure equipment hazard levels that dictate containment form, after all.
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