Grounding Combustible-Dust Equipment Under TRGS 727

Section 5.7 covers portable vacuum cleaners and fixed vacuum installations. Both can generate high charge densities and can themselves become dangerously charged.

Dust-contacting parts must be conductive or dissipative. Conductive parts, particularly conductive suction nozzles, must be grounded. Dissipative parts must connect to conductive parts so that they have earth contact. The dust collection container must remain grounded throughout operation, including emptying.

A vacuum cleaner that cannot be grounded, or lacks a conductive connection between its suction nozzle and collection container, must not be used in explosion-hazardous areas or to collect combustible dusts.

Section 5.7 also requires dissipative filter fabric for dusts with a minimum ignition energy (MIE) of 3 mJ or less. Its separate prohibition on collecting solvent-containing dusts, or operating where flammable gases may form, applies to both vacuum cleaners and fixed vacuum installations.

Section 6.2 addresses bulk materials in the absence of flammable gases and vapors. Within that scope, section 6.2.1 requires conductive and dissipative objects and equipment in explosion-hazardous areas to be grounded in accordance with section 8.

Section 6.2.1 allows grounding to be omitted only if either:

• The conductive or dissipative objects demonstrably do not become charged during intended operation, including possible faults.
• The energy that can be stored on the ungrounded objects is less than the bulk material’s minimum ignition energy.

For assessing ignition sensitivity, the introduction to section 6 uses the MIE of the finest particle fraction that occurs.

Where equipment combines conductive, dissipative and insulating materials, section 6.2 requires all conductive and dissipative parts to be grounded or connected to earth.

Conductive and dissipative containers must be grounded or connected to earth during filling and emptying. Bulk materials and their containers must also be handled or operated so that dangerous charging is avoided.

Where openly adding bulk material to an explosive atmosphere cannot be avoided, section 6.3.3 requires special measures to limit charging. These include conductive, grounded handling aids such as shovels, funnels and chutes, together with grounding of the people involved.

For dissipative packaging, such as paper bags, a note explains that adequate earth contact can be achieved through the person holding it. This approach requires dissipative flooring, footwear and gloves, with contamination not having reduced their dissipative properties.

A hose’s suitability for flammable liquids does not establish its suitability for safe dust transport. TRGS 727 gives bulk-solids pipes and hoses separate provisions for aspiration and pneumatic transport in section 6.4.

When bulk material is conveyed in the presence of flammable gases or vapors, suitable pipes and hoses can prevent ignition-capable discharges from the pipes and hoses. They do not prevent discharges from the conveyed product.

Section 6.5(2) requires all conductive parts to be grounded and dissipative parts of the filter elements to have adequate earth contact.

Under section 6.5(3), insulating filter material may be used to separate combustible dusts only if it does not interrupt the grounding of conductive or dissipative parts of the separator. Filter selection must also satisfy the applicable material requirements in section 6.5.

Earth connections in filtering separators can experience strong mechanical loads. A note to section 6.5(2) therefore calls for recurring checks of grounding or adequate earth contact.

For textiles incorporating conductive or dissipative fibers, such as filter fabrics containing carbon fibers, section 3.2 requires a check after cleaning or particular stress to confirm that conductivity or dissipativity remains across the entire fabric.