# Vent mixture and individual compounds: source-basis audit

5 November 2026. Conditional source calculations, not ambient concentrations or health-risk estimates.

The published composition table supports a stream-by-stream reconstruction of benzene and H2S under explicit flow conventions. It does not yet supply a complete, reconciled flare-tip thermodynamic state. The most useful next records are unrounded stream/emissions worksheets, actual pilot/purge mixing and the separate condensate-tank vent geometry.

## What was checked

Application 455458, Appendix D Table D.1 (physical PDF258), gives 23 composition rows across 11 streams. All 253 printed tokens were retained and checked against the extracted table, with visual review of the source table. Listed sums are 0.999984–1.000014; no normalization was applied. The high-CO2 acid, flash and storage streams have water mole fractions of 0.06482, 0.00821 and zero, respectively. These are compositions including water; the unresolved issue is how the reported dry gas flows were combined with them.

Appendix C (PDF254–255) gives flows of 7,264, 358 and 19.2 standard m³/h for these streams. The application form (PDF5) specifies 20°C, 101.325 kPa, dry basis, while Appendix C uses 23.6449 m³/kmol (approximately a 15°C ideal-gas molar volume). Table 6.5 gives 45°C vent discharge. PDF60 distinguishes physical routing: acid and flash gas to the elevated flare; storage vapour to a tank-top pressure-control vent. The assessment aggregates storage at the flare. These distinctions are retained here.

Original application: https://woodfibrelng.ca/wp-content/uploads/2026/10/Woodfibre-LNG-Project_WDA-Air-Emissions-Permit-Application-Package.pdf

## Conditional compound mass rates

For each stream, mass rate is Q_wet × wet mole fraction × molecular mass / molar volume, converted from kg/h to g/s. Two flow interpretations are tested: the listed flow is already wet; or it is dry and the corresponding wet flow is Q_dry/(1−water fraction). Each is calculated using the Appendix C molar-volume factor and the ideal-gas factor at 20°C, 101.325 kPa. The latter is 24.0551 m³/kmol. These are discrete interpretation tests, not a confidence interval, operating variability, or proven upper/lower bounds.

| Interpretation | Molar-volume basis | Benzene from three diverted streams (g/s) | H2S from three diverted streams (g/s) |
|---|---|---:|---:|
| Listed flows wet | Appendix factor | 0.171 | 0.962 |
| Listed flows wet | Ideal gas at 20°C | 0.168 | 0.946 |
| Listed flows dry; restore water | Appendix factor | 0.180 | 1.028 |
| Listed flows dry; restore water | Ideal gas at 20°C | 0.177 | 1.011 |

These totals exclude normal HP fuel/feed streams and any pilot combustion, destruction, formation or entrainment. They must not be used as final vent emissions, flare benzene emissions, or ambient concentrations. The public Explorer's published total-VOC and H2S inputs have not been replaced. Total VOC is not benzene; this audit does not establish the definition or calculation behind the reported 11.75 g/s total VOC.

Under these branches, the tank stream contributes about 0.027 g/s benzene, or 15–16% of the three-stream total, despite only about 0.25% of their gas volume. This is a reason to recover and model its separate physical source, not evidence that it dominates exposure in any community. The amount reaching a receptor depends on release height, momentum, surroundings and weather.

Printed precision matters. The acid-gas benzene entry is 0.00002 (20 ppm by volume). If rounded to the nearest last printed digit, it represents 15–25 ppm. Holding the wet/Appendix branch and applying analogous flow/other printed precision gives about 0.137–0.204 g/s for the three-stream sum. This is a conditional rounding envelope, not statistical uncertainty; zeros have no documented detection limits. Unrounded inputs matter more here than the approximately 1.7% difference between the two molar-volume factors.

Appendix C uses 326 ppm acid-gas H2S and 6 ppm feed-gas H2S; Table D.1 prints 330 and 10 ppm. Those values fit within rounding-to-nearest intervals of the printed D.1 cells, so they are not established contradictions. Reconstructing Appendix C's H2S rates including the normal feed contribution gives about 0.951 g/s, close to but not exactly the application’s 0.948 g/s. This does not identify which flow convention the worksheet actually used or establish an application error.

## Water and thermodynamic implications

For acid plus flash gas before pilot mixing, both flow interpretations yield approximately 6.2 mol% water. At 1 atmosphere and 45°C, ideal partial pressure is about 66% of water saturation pressure. Cooling this unmixed, constant-pressure composition gives a water dew point near 37°C. The Antoine equation and coefficient range were taken from NIST; every calculated temperature stays within the stated range.

This is a water-only equilibrium diagnostic. It neither establishes all components are gaseous nor predicts cloud condensation, visible plume, PM2.5 or latent heat along a real trajectory. Entrainment changes water fraction and temperature together. The result reinforces the need for a mixture/phase treatment when considering a pure-substance dense-gas surrogate. Full heat capacity, unknown sulphur constituents, other condensation, pilot heat and actual tip mixing remain uncharacterized.

Property sources:
- Benzene molecular mass 78.1118 g/mol: https://webbook.nist.gov/cgi/cbook.cgi?ID=71-43-2
- H2S molecular mass 34.081 g/mol: https://webbook.nist.gov/cgi/cbook.cgi?ID=C7783064&Mask=40
- Water mass and Antoine coefficients (304–333 K, pressure in bar): https://webbook.nist.gov/cgi/cbook.cgi?ID=C7732185&Type=ANTOINE

## Verification and use

The retained protocol predates the calculations. Checks cover 253 original composition tokens, 36 mass-rate recalculations through alternative unit paths, six separate Decimal benzene reconstructions from the original extracted table, composition closure, dew-point inversion/range and the H2S rounding interpretation. They verify transcription and arithmetic, not actual release conditions or model performance.

The next model step is to reconcile source flow, phase and pilot mixing and represent the tank vent separately before adding a species-specific community layer. The existing public application-results summary remains the stronger site-specific concentration evidence; its missing community outputs should be sought directly. No external records request has been sent, and no new dispersion run or health-risk claim follows from this audit.