UPDATED on 4/4/24 with 2024 ERG Info
This week we saw the official release of the 2020 Emergency Response Guide (ERG) from DOT/PHMSA and along with this 2020 update came some clear distinctions between a “Heat Induced Tear” (HIT) and a Boiling Liquid Expanding Vapor Explosion (BLEVE).
(emphasis by PHMSA)
A Heat Induced Tear (HIT) is a rupture of a NON-PRESSURE tank car containing flammable liquids when exposed to the intense heat of a fire. The metal will soften and the pressure in the tank car will increase which can lead to containment failure. The tear generally occurs at the vapor space (upper side) of the container, venting large quantities of flammable liquid and vapors at high speed. A fireball and an intense heat wave will occur. Compared to BLEVEs, HITs rarely result in the projection of tank car fragments. Heat induced tearing has occurred within 20 minutes of the derailment and as long as 10+ hours following the initial fire.
Responding to these types of incidents (BLEVE and HIT) requires specialized training, equipment and a tactical approach.
UPDATED with 2024 ERG Info
This document presents important safety-related information on BLEVEs to consider in a situation involving Liquefied Petroleum Gases (LPG), UN1075.
LPGs include the following flammable gases:
- UN1011 – Butane
- UN1012 – Butylene
- UN1055 – Isobutylene
- UN1077 – Propylene
- UN1969 – Isobutane
- UN1978 – Propane
A BLEVE occurs when a fire-impinged or damaged tank car fails to contain its internal pressure and explodes with a sudden product release. This catastrophic failure is more likely to occur with damaged pressure tank cars, even in the absence of an active fire.
The main hazards from a LPG BLEVE are:
- Fire: If the released substance is ignited, there is an immediate fireball.
- Thermal radiation: At a distance of about 4 times the radius of a fireball, the heat radiated from a fireball is enough to burn exposed skin in 2 seconds. Wearing protective clothing limits the thermal radiation dose.
- Blast: A concussive force caused by the sudden release of the pressurized substance. For a BLEVE occurring out in the open, the blast strength at a distance of 4 times the radius of a fireball can break window glass and may cause minor damage to buildings.
- Projectiles: Tank failure can throw metal fragments over large distances. These fragments can and have been deadly.
The danger decreases as you move away from the BLEVE center. The furthest-reaching hazard is projectiles.
For a video with information on critical safety issues concerning BLEVEs, please visit https://www.tc.gc.ca/eng/tdg/publications-menu-1238.html.
HEAT-INDUCED TEAR (HIT)
A heat-induced tear (HIT) is a rupture of a NON-PRESSURE tank car containing flammable liquids when exposed to the intense heat of a fire. The metal will soften and the pressure in the tank car will increase which can lead to containment failure. The tear generally occurs at the vapor space (upper side) of the container, venting large quantities of flammable liquid and vapors at high speed. A fireball and an intense heat wave will occur.
Compared to BLEVEs, HITs rarely result in the projection of tank car fragments.
Heat-induced tearing has occurred within 20 minutes of the derailment and for as long as 10+ hours following the initial fire.
Responding to these types of incidents (BLEVE and HIT) requires specialized training, equipment, and a tactical approach.