Pressure Relief Vent
How does WorkSafeBC define and regulate pressure relief vents versus other PRDs?
WorkSafeBC uses 'pressure relief device' for any device that relieves pressure by venting fluid. Key requirements include: set pressure ≤ 103 kPa (15 psi) unless engineer approves, flow capacity ≥ pressure source, discharge to a safe location, no valves in discharge unless locked, and piping sloped to avoid freezing. These apply to pressure relief vents as PRDs.
What engineering criteria apply to sizing and set pressure of a pressure relief vent?
Set pressure must not exceed the lowest-rated component's pressure rating, often at ~110% of MAWP for non-fire cases. Capacity must handle worst-case scenarios like blocked discharge or fire, with flow capacity ≥ pressure source per WorkSafeBC. Discharge piping must maintain full cross-section and avoid restrictions.
How must the discharge of a pressure relief vent be designed to comply with WorkSafeBC?
Discharge must be to a safe location away from workers, doors, windows, and air intakes. Piping must be as short and straight as possible, sloped for drainage, protected from freezing, and have no downstream isolation valves unless locked. This ensures no worker is endangered during discharge.
A pressure relief vent is a pressure relief device that automatically vents gas or liquid from an enclosure, vessel, or pressurized system when internal pressure exceeds a specified limit, preventing structural failure or explosion. It directs discharge to a safe location, such as atmosphere or a collection system, to protect workers from harm, as required by WorkSafeBC and ASME standards.
On a shop floor, pressure relief vents are critical for safety in pressure vessels, piping systems, and purged electrical enclosures. For compressed air receivers or chemical reactors, they prevent overpressure from blocked discharge or pump dead-heading, with discharge piped safely outside. In hazardous locations, vents on purged enclosures control overpressure and release purge gas. Gas cylinders and chemical tanks also use vents to relieve pressure from fire or runaway reactions. Operators must keep vents unobstructed and avoid isolation valves to ensure compliance with WorkSafeBC regulations.
Inadequate vent sizing or incorrect set pressure, such as sizing only for normal flow instead of worst-case scenarios like blocked positive displacement pump discharge, leading to overpressure and vessel rupture.
Unsafe discharge location or obstructed vent path, including venting into building interiors near workers, doors, or air intakes, or allowing liquid accumulation or freezing in discharge piping, endangering workers.
Isolation valves, tampering, or lack of inspection, such as installing valves between pump discharge and relief device, closing isolation valves to stop nuisance venting, or neglecting periodic testing and recalibration, disabling overpressure protection.