04 Apr Electrical Safety – Static Electricity
Static Electricity
Static electricity is something most people have experienced. Walking across carpet and touching a metal object can produce a small spark. In everyday situations, that spark is usually little more than a surprise. In a workplace containing flammable liquids, vapors, gases, or combustible dusts, however, a static discharge can become an ignition source capable of causing a serious fire or explosion.
Understanding how static electricity develops—and how to control it—is an important part of working safely around flammable and combustible materials.
How Static Electricity Develops
Static electricity can develop when materials come into contact and then separate. Electrical charges can accumulate on materials, equipment, containers, piping, or personnel. If sufficient charge builds up, it may suddenly discharge as a spark.
Static charge can be generated during many routine operations, including:
- Transferring flammable or combustible liquids between containers.
- Pumping liquids through pipes, hoses, or filters.
- Filling or emptying tanks, drums, and containers.
- Spraying liquids or ejecting droplets or particles from a nozzle.
- Mixing, agitating, or filtering liquids.
- Handling powders and other finely divided materials.
- Moving combustible dust through ducts or collection systems.
- Movement of belts, conveyors, or other equipment.
- Separating certain plastic or synthetic materials.
- Sliding synthetic rope through gloves or other materials.
Dry conditions can increase static accumulation, but workers should never assume that static electricity cannot develop because conditions are humid.
Why Static Electricity Is Dangerous
A static spark becomes especially dangerous when it occurs where a flammable atmosphere is present.
A fire or explosion can occur when three basic conditions exist:
- A flammable vapor, gas, or combustible dust is present in an ignitable concentration.
- Sufficient oxygen is present.
- A static discharge or another ignition source supplies enough energy for ignition.
The spark may be extremely small and may occur without warning.
Bonding and Grounding
Bonding and grounding are common methods of controlling static electricity during operations involving flammable materials.
Bonding electrically connects two conductive objects so that a dangerous difference in electrical potential does not develop between them.
Grounding connects conductive equipment to an appropriate grounding point so accumulated electrical charge can dissipate.
When required:
- Bond conductive containers before transferring flammable liquids between them.
- Establish bonding and grounding connections before beginning the transfer.
- Maintain the connections throughout the transfer operation.
- Attach clamps to clean, conductive surfaces that provide reliable electrical contact.
- Inspect bonding and grounding cables, clamps, and connections before use.
- Do not disconnect bonding or grounding connections until the transfer operation is complete.
- Use only equipment, hoses, containers, and transfer systems suitable for the material and operation.
Simply placing a container on the ground does not necessarily provide effective electrical grounding.
Nonconductive Materials
Plastic containers, hoses, liners, clothing, and other nonconductive materials can present special problems because accumulated static charge may not readily dissipate through conventional grounding.
Do not assume that attaching a grounding clamp to a nonconductive object will eliminate the hazard.
Where static accumulation is possible, use equipment and materials specifically designed for the operation and follow the manufacturer’s procedures and the company’s hazardous-material handling requirements.
Other Ways to Control Static Hazards
Depending on the operation, static hazards may also be controlled by:
- Using properly designed conductive or static-dissipative equipment.
- Controlling the rate at which liquids are transferred.
- Avoiding unnecessary splashing, spraying, or free-falling liquids.
- Using properly designed fill pipes and transfer equipment.
- Maintaining conductive continuity throughout transfer systems.
- Eliminating unnecessary ignition sources.
- Using ventilation to prevent accumulation of flammable vapors.
- Controlling combustible dust accumulation through proper housekeeping and dust-control systems.
- Substituting materials or processes that generate less static electricity when feasible.
Static-control methods must be appropriate for the particular substance, equipment, and operation.
Before Transferring Flammable Liquids
Before beginning a flammable-liquid transfer:
- Identify the material and review its Safety Data Sheet (SDS).
- Eliminate smoking, flames, sparks, and other ignition sources.
- Verify that containers and transfer equipment are approved for the material.
- Establish required bonding and grounding.
- Confirm that ventilation is adequate.
- Inspect hoses, fittings, pumps, and connections.
- Control spills and promptly clean up released material using approved procedures.
- Keep containers closed when they are not being filled or emptied.
Never improvise bonding or grounding arrangements when handling flammable materials.
Remember
A static spark that is harmless in an office or home can be disastrous in an atmosphere containing flammable vapors, gases, or combustible dust.
Control the fuel, eliminate ignition sources, and use proper bonding and grounding whenever required. A few moments spent controlling static electricity can prevent a fire, explosion, serious injury, or fatality.