GCSE PHYSICS - Electrostatic Charge - How can Fuels or Powders flowing through a pipe cause an Explosion?

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What are the Dangers of Electrostatic Charge?

When charge jumps across an air gap it causes a spark.
The spark can ignite (set fire to)
flammable liquids, vapours and powders in pipes.

How can Fuel Flowing through a Pipe cause an Explosion?

Care must be taken to avoid sparks when putting fuel in
cars or aircraft. The fuel itself is an insulator (a hydrocarbon)
and charge can be transferred as the fuel flows through
a pipe if the pipe is also an insulator. The transfer of charge
happens because there is friction between the fuel and
the pipe. As the nozzle (the end) of the pipe is brought
close to the fuel tank, a spark can jump between the two
igniting the fuel. This can cause a serious explosion,
particularly with aircraft which are filled at a very high speed.

The spark can be avoided if the pipe nozzle
is made to conduct by connecting an earthing strap to it
and so any charge can be safely conducted away.
An earthing strap connects the pipe to the ground (the Earth).
In addition, a cable can connect the pipe to the fuel tank,
so that there can be no difference in charge between them.

How can Powder Flowing through a Pipe cause an Explosion?

There is a very similar situation with powders in pipes.
If the powder is an insulator then charge is transferred
between the pipe and the powder in the same way
as fuel in pipes (see above). A spark can ignite a powder
just like it can ignite a flammable liquid or vapour.
A powder can burn very quickly because it has a very
large surface area and this can cause an explosion.

The way to avoid an explosion is the same as above.
Use an earthing strap between the pipe and the earth
and any charge can be safely conducted away.

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