A blowdown stack is a chimney

Chimney

A chimney is a structure for venting hot flue gases or smoke from a boiler, stove, furnace or fireplace to the outside atmosphere. Chimneys are typically vertical, or as near as possible to vertical, to ensure that the gases flow smoothly, drawing air into the combustion in what is known as the...

 or vertical stack that is used to vent the pressure of components of a chemical, refinery or other process if there is a process problem or emergency. A blowdown stack can be used to complement a flare stack or as an alternative. The purpose is to prevent 'loss of containment' of volatile liquids and gases.

The failure of the blowdown stack to contain hydrocarbon

Hydrocarbon

In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

s vented from a raffinate splitter led to a catastrophic explosion

Explosion

An explosion is a rapid increase in volume and release of energy in an extreme manner, usually with the generation of high temperatures and the release of gases. An explosion creates a shock wave. If the shock wave is a supersonic detonation, then the source of the blast is called a "high explosive"...

 at the Texas City Refinery (BP)

Texas City Refinery (BP)

On March 23, 2005, a fire and explosion occurred at BP's Texas City Refinery in Texas City, Texas, killing 15 workers and injuring more than 170 others. BP was charged with criminal violations of federal environmental laws, and has been subject to lawsuits from the victims' families...

in 2005.