Dangers of Static Electricity

1. Dangers of Static Electricity Part 4a(part2)

2. Starter In pairs, discuss and write down everything you know about electric shocks and how they can be prevented.

3. Learning Objectives • Must: know how you can get an electrostatic shock • Should: know how static electricity can be dangerous • Could: know how to reduce the chance of getting an electric shock

4. Electric shocks • A person gets an electrostatic shock if they become charged and then become earthed. • E.g. a person can become charged if they walk on a nylon carpet or vinyl floor because: • 1) the floor is an insulator • 2) they become charged as they walk due to friction. • The person can become earthed by touching water pipes or even another person.

5. When Static electricity is dangerous

6. Static electricity is dangerous in conditions where there are explosive materials. • When inflammable gases or vapours are present or there is a high concentration of oxygen, a spark from static electricity could ignite the gases or vapours and cause an explosion. • Mobile phones should not be used on petrol station forecourts to prevent sparks that could cause an explosion

7. How are explosions prevented in the tanks of oil tankers during cleaning? • When cleaning oil tankers their tankers are first filled with an inert gas such as nitrogen to avoid a spark that could cause an explosion.

8. Current, voltage and resistance • If a person touches something at a high voltage, large amounts of electric charge may flow through their body to earth. • Current is the rate of flow of charge. • The voltage that produces a given current depends on the resistance. • If a person is barefoot and sweaty, resistance is low and the current is greater for a given voltage.

9. Lorries containing inflammable gases and liquids are always earthed before they are unloaded. This prevents a spark igniting the gas or liquid. Any build up of charge immediately flows down the earth wire. Safety Measures

10. In a factory where machinery is at risk of becoming charged, the operators stand on insulating rubber mats so that charge cannot flow through them to earth. • Shoes with insulating soles are worn by workers if there is a risk of charge building up so that charge cannot flow through them to earth.

11. Dangers of Charge Fuel filling, paper rollers and grain shoots are all charge problems. As the fuel flows along the pipe or paper rolls over rollers or grain shoots out of tubes, static can build up. This can easily lead to a spark and then an explosion. To prevent this happening, the nozzles or rollers are made out of metal so any charge build up is conducted away. Large petrol tankers always have earthing straps between the tanker and the storage tank to prevent the risk of sparks.

12. When refuelling an aeroplane, special measures have to be taken to avoid any explosions.Watch this video

13. Transferring flammable liquids What prevents large static charges building up that could cause a possible explosion? nozzle from tanker underground tank or aeroplane tank. electrical link

14. Anti-static devices • Sprays, liquids and dusters made from conducting materials carry away electric charge. This prevents a build up of charge that could be dangerous or a nuisance. • ‘Dryer sheets’ containing oil are used in tumble dryers to prevent static charging.

15. What have you learned? • Can you list three problems with static electricity. • What are the ways we can reduce the chances of getting an electric shock?