September 2024 | AIChE

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September 2024

Vapor Collection System

A piping system to which vessels are connected, that collects vapors from these vessels and directs them to environmental control equipment such as flares, incinerators, scrubbers, and activated carbon adsorbers.

Vapor Cloud Explosion (VCE)

The explosion resulting from the ignition of a cloud of flammable vapor, gas, or mist in which flame speeds accelerate to sufficiently high velocities to produce significant overpressure.

Vapor

The gaseous phase formed by a material that is liquid at ambient temperature and pressure.

Upper Flammable Limit (UFL)

The highest concentration of a vapor or gas (the highest percentage of the substance in air) that will produce a flash of fire when an ignition source (heat, arc, or flame) is present. See also Lower Flammable Limit. At concentrations higher than the UFL, the mixture is too rich to burn. Also known...

Update and Revalidate

To revise a prior PHA, as required, to reflect any changes that have occurred since the prior PHA; new learnings about the hazards of the process; changes in risk management requirements; etc.

Unstable Substance/Material

Substance or material which in a pure state or as normally produced decomposes either or not violently.

Unstable material

A material that, in the pure state or as commercially produced, will vigorously polymerize, decompose or condense, become self-reactive, or otherwise undergo a violent chemical change under conditions of shock, pressure, or temperature. (NFPA 704, 2001 edition)

Unstable Detonation

See Overdriven Detonation.

Unstable

Tending toward decomposition or other unwanted chemical change during normal handling or storage. Importance: A MSDS will list materials that are unstable and conditions to avoid to prevent decomposition or unwanted chemical changes.

Unrevealed Faults

A failure may lie dormant in the system and only be discovered as a result of a thorough diagnostic testing procedure.

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