Single-source hazardous-area classifier per IEC 60079-10-1:2020 Annex B/C: computes release rate for gas jets, flashing liquids, and pool evaporation, determines zone type (0/1/2, NE) from the grade × ventilation matrix, fits the hazardous-radius (zone extent) curve, and recommends Ex protection markings. Hard-refuses catastrophic (>1 kg/s), mist, and other out-of-scope releases.
Gas releases: isentropic orifice flow, choked or subsonic depending on whether the ambient/upstream pressure ratio is below the critical ratio. Flashing liquids: Bernoulli jet when subcooled, Fauske/HEM (homogeneous equilibrium) when saturated, with a flash-fraction estimate. Pools: Mackay-Matsugu mass-transfer evaporation correlation. All three feed a release characteristic W_g that drives the Annex C zone-extent curve fit; zone TYPE comes from a separate IEC Table B.1 grade×ventilation×availability×indoor decision matrix (not from W_g).
Applies when P_a/P_1 is below the critical ratio (2/(γ+1))^(γ/(γ-1)); R_s = R/MW is the specific gas constant. The subsonic form (Eq B.2) is used otherwise: Q_m = C_d A P_1 √[2γ/((γ-1)R_s T_1)·((P_a/P_1)^(2/γ) − (P_a/P_1)^((γ+1)/γ))].
Homogeneous-equilibrium model for a saturated liquid jet (P_1 ≤ ~1.05·P_sat(T_1)); the subcooled case instead uses incompressible Bernoulli: Q_m = C_d A √(2ρ_L(P_1−P_sat)). Flash fraction x = c_{p,L}(T_1−T_sat)/h_fg, clipped to [0,1].
Zone extent — release characteristic & curve fit (Annex C Figure C.1)
Wg=k⋅LFLQgextent=aWgb
k = 0.25 (toxic) / 0.5 (default) / 1.0 (low-risk) per §6.4.2; Q_g is the standard-condition volumetric release rate. a = 12.7, b = 0.48 fitted to three published Annex C reference points; validated to ±15% against IEC Annex E worked examples (the standard's own method is ±20%).
