Dangers of static electricity revision notes

Edexcel International GCSE Physics (4PH1), chapter 9: Electric charge, specification point 2.27P. Free lesson.

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Static charge can build up when materials rub together, then escape as a spark. Sparks can ignite fuel vapour or damage electronics, so bonding and earthing provide a path for electrons to flow away before charge builds up.

How charge builds up during refuelling

Fuel is pumped through a hose at high speed. As it rubs against the inside of the hose, friction transfers electrons between the fuel and the hose. Charge then builds up on the aircraft or tanker. The charge cannot easily escape, so the voltage between it and the ground gets larger. The process begins with fuel rubbing against the pipe or hose. Electrons are transferred, causing charge to build up.

Why a spark is dangerous

When the voltage becomes large enough, electrons can jump across the gap through the air. This sudden movement of electrons is a spark. Fuel gives off vapour, and the spark can ignite it, causing a fire or explosion. Charge builds up, the voltage rises, and a spark jumps across the gap. The spark can ignite fuel vapour.

How bonding and earthing prevent sparks

Bonding joins the aircraft and fuel tanker with a metal cable. Earthing connects them to the ground. The cable lets electrons flow away as quickly as charge forms, so charge does not build up and a spark cannot jump. Before fuel is unloaded, connect the tanker or aircraft to earth with a cable. Electrons flow through the cable to or from earth. Only electrons move. A negative object loses electrons to earth. A positive object gains electrons from earth.

Other hazards from static electricity

Static charge can build up in many situations, then escape suddenly as a spark or shock. The size of the effect varies, but the cause is the same: charge builds up and then moves away. Lightning is a huge spark from charge built up in storm clouds to the ground. Sliding off a car seat can charge you. Touching the metal door can cause a small shock as electrons jump across. Shoes rubbing on a synthetic carpet can charge you, then touching a metal door handle can give you a shock. A small spark near computer parts can damage the chips.

How to explain the hazard and its solution

For a refuelling question, link each stage from friction to fire, then explain how earthing stops charge from building up. The same idea explains why workers handling computer chips wear a wrist strap connected to earth.