In a hazardous (explosive-atmosphere) duty, a fibre-reinforced plastic fan must not generate or hold a static spark, so conductive surfaces and verified grounding are mandatory, confirmed by spark testing.
The Static Hazard in FRP
FRP is an insulating composite, which is why it resists corrosion in acid and solvent-laden air, but that same insulation lets charge build on the impeller as it moves particulate-laden or low-conductivity gas. A spark jumping to the housing can ignite a flammable mixture. The fix is to make the wetted surface sufficiently conductive (via carbon loading or a conductive liner) and to bond the assembly to earth so charge drains instead of accumulating to a breakdown voltage. Simply painting the outside conductive does nothing if the gas-wetted inside stays insulating.
Zones matter: a Zone 1 (continuously hazardous) duty demands a higher surface conductivity and documented bonding than a Zone 2 intermittent area, and the choice of zone drives both the material specification and the test rigor, so stating the zone on the enquiry is not optional for this equipment.
Material selection sits alongside the static question. The resin decides the chemical range: a vinyl ester system handles strong acids and oxidisers that would attack a general-purpose polyester, and each resin family carries a service temperature limit, commonly in the region of 80 to 120°C for continuous duty, well below what a steel fan tolerates. Wall thickness and the reinforcement schedule set the mechanical margin, and because composite fatigue behaviour differs from steel, tip speed is usually held lower than an equivalent metal wheel would allow. Specifying gas composition, concentration, temperature, and moisture content is therefore the starting point, since the same duty in a drier stream may not need a composite fan at all.
Spark Testing and Grounding
Spark testing applies a high voltage between the conductive layer and ground to prove there is no breakdown and that the layer is continuous. A resistance measurement from impeller to ground confirms the bond is below the required threshold, often a few megaohms or less depending on the standard cited. The whole rotating and static assembly is bonded to a single earth point so no part floats at a dangerous potential relative to the rest of the system.
| Item | Specification | Note |
|---|---|---|
| Surface type | Conductive liner | Carbon-loaded FRP |
| Bond resistance | < 10 MĪ© | Impeller to earth |
| Test voltage | Per standard | Spark/continuity check |
| Zone | 1 / 2 | Drives conductivity level |
| Earth point | Single bonded | No floating parts |
| Resin service limit | ≈ 80–120°C | Continuous duty, resin dependent |
| Bonding straps | Checked at every joint | Flexible connections bridged |
Beyond the fan, the duct and any filter housing in the same hazardous area must share the same bonding scheme, or the fan is grounded while the rest of the system is a latent source. A spark can jump from whatever is charged, so the entire gas path has to be treated as one bonded conductor.
Conductivity is not permanent, which is why the test belongs in the maintenance plan as well as the factory record. Abrasive particulate slowly wears the conductive liner at blade leading edges and around the wheel eye, and a repair carried out with standard resin can leave an insulating patch exactly where charge concentrates. Resistance from impeller to earth should be re-measured after any repair and on a defined interval, typically annually for continuous hazardous-area service. Flexible duct connections need bonding straps across them because the flexible itself is an insulator, and a shaft-seal purge or an earthing brush may be specified where a bearing grease film would otherwise break the path to earth.
Safety Checklist
- Specify the zone: State Zone 1 or 2 so the right conductivity level is built in at the factory.
- Require the test: Ask for the spark/continuity report, not just a material claim on the drawing.
- Bond the system: Duct, fan, and filter share one earth, no floating parts anywhere.
- Avoid insulators: Non-conductive inserts in the gas stream need special approval for the zone.
- Verify on site: Re-check resistance after installation, because handling can break a bond.
- State the gas stream: Give composition, temperature, and moisture so resin and liner are chosen on data, not on habit.
- Re-measure after repair: Any patch on the conductive liner needs a fresh resistance check before return to service.
Why Verification Matters
A static-safe FRP fan is safe only if its conductivity and bonding are proven, not assumed from the resin type. Keruite builds corrosive-duty fans with conductive, spark-tested liners and documented bonding so the unit is fit for the declared hazardous zone, and the inspector gets the evidence rather than an assurance.
Hazardous-area equipment is bought on evidence, because nobody can inspect conductivity by eye once a unit is installed. Corrosion-duty fans fabricated in an 80,000 m² plant by a manufacturer with more than 30 years of experience are supplied with measured bond resistance and liner specification recorded against the serial number, and an in-house performance laboratory confirms the aerodynamic duty on the same unit. ISO 9001:2015 covers the lay-up and test records, CCC certification covers the motor and electrical package, and with deliveries to more than 50 countries the documentation references the zone classification the local authority actually uses.
Our engineers respond to selection enquiries within 24 hours, including conductive liner and grounding verification for FRP fans in hazardous areas.