How charge is generated and accumulates
Contact and separation between materials, product movement and certain transport operations can separate charges. Accumulation depends on conductivity, surfaces, the environment and opportunities for dissipation.
The problem is not limited to energised electrical installations. A person, container or insulating material can become charged during a routine operation. The absence of a power cable does not rule out this risk.
When a discharge is hazardous
An uncomfortable discharge in an office is not equivalent to a process involving flammable vapours or combustible dust. Ignition depends on the characteristics of the mixture and discharge, not merely on whether someone notices a spark.
Royal Decree 681/2003 expressly includes electrostatic discharges among ignition sources to be assessed. Assessment of explosive atmospheres must consider substances, installations, operations and interactions together.
What to review in the assessment
- Materials and substances present, including waste and cleaning products.
- Charge-generating operations and foreseeable abnormal situations.
- Conductive components that may become isolated.
- The presence and duration of flammable atmospheres.
- Clothing, footwear, floors and compatibility with the combined measures.
- Changes to materials, equipment, cleaning or environmental conditions.
Checks must reflect the actual scenario and be carried out by competent personnel. A measurement outside the critical operation may not represent the problem.
Controlling generation, accumulation and discharge
INSST Technical Note NTP 567 describes different groups of measures: material selection, equipotential bonding and earthing of conductive components, dissipative solutions and control of process conditions.
The combination requires technical design. Earthing a conductive object does not automatically remove charge from an insulating material. Nor is buying an item labelled antistatic enough if the rest of the system prevents charge dissipation.
Limits of humidity and isolated solutions
Increasing humidity may promote dissipation in certain materials, but effectiveness depends on surfaces and the process. Some insulators do not respond sufficiently; it must not be treated as a universal guarantee against ignition.
Neutralisation equipment must also suit the environment. Devices must not be introduced into explosion-risk areas without checking their suitability. Static control solutions must be compatible with protection against electric shock.
Verification and maintenance
Effectiveness may be lost through corrosion, faulty connections, insulating coatings, wear or changes in cleaning products. Reviews must check relevant components and record anomalies and corrections.
In installations with explosive atmospheres, measures must be integrated into the explosion protection document and reviewed after significant changes. Training explains which conditions must not be altered and when to stop the activity to request technical checks.
Hypothetical example: changing containers
A company replaces containers in a process with ones made from a different material. Although the operation appears identical, the preventive team identifies changed possibilities for charge dissipation.
Before accepting the change, materials, substances, connections and operating conditions are reviewed. The example shows why retaining a bonding clamp does not, by itself, demonstrate that the new arrangement maintains the previous protection.
