Screens the ignition risk of a spark discharge from an isolated conductive part (e.g. an ungrounded metal fitting, a person, a plastic container with an induced charge) by computing its stored capacitive discharge energy and comparing it against the surrounding atmosphere's Minimum Ignition Energy (MIE) — the standard first-pass electrostatic hazard check referenced by IEC 60079-32-1.
Standards followed
IEC 60079-32-1 (electrostatic hazards, protection and equipment in hazardous areas) — screening method basisIEC 60079-20-1 (material characteristics, incl. MIE, for gases/vapors) — the source for substance-specific MIE data, entered by the user
What it can do
- Capacitive discharge energy: E = ½CV², from the part's capacitance to ground and its charged voltage.
- Pass/fail comparison against a user-supplied Minimum Ignition Energy (MIE) for the specific substance.
- Margin factor showing how many times below (or above) the MIE the computed spark energy is.
- General gas-group guidance (IIA/IIB/IIC) on typical MIE ranges, since a gas's group classification is itself driven by how easily it ignites.
Example problem
An isolated metal part with 100pF capacitance charged to 10,000V, in an atmosphere with MIE = 0.25mJ (typical propane-range value).
- E = 0.5 × 100×10⁻¹² F × (10,000V)² = 0.5 × 100×10⁻¹² × 10⁸ = 0.005 J = 5mJ.
- 5mJ is 20× higher than the 0.25mJ MIE — this discharge energy exceeds the ignition threshold.
5mJ spark energy vs. 0.25mJ MIE — FAILS (ignition risk). (100pF/10kV is a deliberately high example to illustrate a failing case; well-bonded plant equipment normally has much lower stray capacitance and is kept below charging voltages that could produce this.)
Want the full step-by-step version?
MIE is a substance-specific property with no single universal value — always use the specific gas/vapor/dust's own tested MIE data (e.g. from IEC 60079-20-1 or the material safety data), not a generic assumption. This is a screening calculation for isolated-conductor discharges — it doesn't cover brush discharges, propagating brush discharges, or bulking-powder discharges, which have their own (often lower) effective ignition energy thresholds and require specialist assessment.