A pool fire occurs when a flammable liquid forms a puddle on the ground and catches on fire. Thermal radiation is the primary hazard associated with a pool fire. Other potential pool fire hazards include smoke, toxic byproducts from the fire, and secondary fires and explosions in the surrounding area
At equilibrium, molecules move from the liquid to the gas phase at the same rate as they return to the liquid from the gas phase. In liquids that are mixtures of chemicals, each component vaporizes (evaporates) at its own characteristic rate. The partial pressure of a chemical in a mixture is a measure of the concentration of that chemical’s gas-phase molecules in the air directly in contact with the liquid. In most actual cases equilibrium is not reached so the partial pressure represents the limiting value for chemical concentration in the air.
Refers to the sudden onset of a pressure wave after an explosion. This pressure wave is caused by the energy released in the initial explosion—the bigger the initial explosion, the more damaging the pressure wave.
A burning and expanding gas cloud formed during a BLEVE of a flammable chemical. The fireball is made up of both the chemical that flash-boils when the tank fails and the chemical that sprays out as an aerosol during the explosion. The primary hazard associated with a fireball is thermal radiation.
Rapid, sharp combustion with sudden evolution of flame. The flame front travels relatively slowly (subsonic speeds), as compared to a supersonic detonation.
This is a type of explosion that can occur when a vessel containing a pressurized liquid is ruptured. Such explosions can be extremely hazardous.
A BLEVE can occur in a vessel that stores a substance that is usually a gas at atmospheric pressure but is a liquid when pressurized (for example, liquefied petroleum gas). The substance will be stored partly in liquid form, with a gaseous vapor above the liquid filling the remainder of the container.
If the vessel is ruptured – for example, due to corrosion, or failure under pressure – the vapor portion may rapidly leak, dropping the pressure inside the container and releasing a wave of overpressure from the point of rupture. This sudden drop in pressure inside the container causes violent boiling of the liquid, which rapidly liberates large amounts of vapor in the process. The pressure of this vapor can be extremely high, causing a second, much more significant wave of overpressure (i.e., an explosion) which may completely destroy the storage vessel and project it as shrapnel over the surrounding area.
A BLEVE does not require a flammable substance to occur, and therefore is not usually considered a type of chemical explosion. However, if the substance involved is flammable, it is likely that the resulting cloud of the substance will ignite after the BLEVE proper has occurred, forming a fireball and possibly a fuel-air explosion. BLEVEs can also be caused by an external fire nearby the storage vessel causing heating of the contents and pressure build-up
A measure of the tendency of air to move upward or downward
within the atmosphere, generating turbulence. The atmosphere may be more or less turbulent at any given time, depending on the amount of incoming solar radiation as well as other factors. Meteorologists have defined six atmospheric stability classes, from A to F, each representing a different degree of turbulence in the atmosphere. When moderate to strong incoming solarradiation heats air near the ground, causing it to rise and generating large eddies, the atmosphere is considered unstable.
Unstable conditions are associated with atmospheric stability classes A and B (air has a strong tendency to move up or down, and the atmosphere is more turbulent). When solar radiation is
relatively weak or absent, air near the surface has a reduced tendency to rise and less turbulence develops. In this case, the atmosphere is considered stable, the wind is weak, and the stability class would be E or F. Stability classes D and C represent conditions of more neutral stability (moderately turbulent).Neutral conditions are associated with relatively strong windspeeds and moderate solar radiation.
The sum of the atomic weights of all the atoms in the molecule
(the weight of one molecule of the chemical).
The Immediately Dangerous to Life or Health level is a limit originally established for selecting respirators for use in workplaces by the National Institute for Occupational Safety and Health. A chemical’s IDLH is an estimate of the maximum concentration in the air to which a healthy worker could be exposed without suffering permanent or escape-impairing
health effects
A threshold value of a hazard (toxicity, flammability, thermal radiation, or overpressure); the LOC is usually the value above which a threat to people or property may exist. For each LOC you choose, ALOHA estimates a threat zone where the hazard is predicted to exceed that LOC at some time after a release begins.
