Blast Fume Clearance Time
Re-entry time for a blasted heading from airway volume, airflow and the dilution ratio (perfect-mixing model).
The logarithmic decay model (perfect mixing) sets the FLOOR for re-entry time — stratified fume in long headings clears slower than the math. Most codes demand both a calculated time and a tested gas reading at re-entry; this calculator provides the first number and the discipline for the second.
Formula
Note: Mine ventilation is statutory and life-safety territory: airflow quantities, gas limits and re-entry times must be set by the registered ventilation engineer/manager under your jurisdiction's mining regulations — this calculator is a planning and training aid.
Re-entry time for a blasted heading from airway volume, airflow and the dilution ratio (perfect-mixing model). A free mine ventilation & air quality tool — no sign-up, no upload, instant results in your browser.
About Blast Fume Clearance Time
Blast Fume Clearance Time computes the governing relationship t = (V/(Q·η)) · ln(C₀/C_t) live as you type. The logarithmic decay model (perfect mixing) sets the FLOOR for re-entry time — stratified fume in long headings clears slower than the math. Most codes demand both a calculated time and a tested gas reading at re-entry; this calculator provides the first number and the discipline for the second. Defaults are pre-filled with realistic values for this exact scenario, and the worked example substitutes your numbers step by step so the math is never a black box.
How to use Blast Fume Clearance Time
- 1Enter your values — Heading volume, Airflow delivered to face, Initial contaminant index, Safe re-entry index and more (sensible defaults are pre-filled).
- 2Read the live results: Clearance time, Air changes needed.
- 3Check the "with your numbers" line to see t = (V/(Q·η)) · ln(C₀/C_t) substituted step by step.
- 4Adjust inputs until the scenario matches yours, then copy or share the result.
Why use Blast Fume Clearance Time?
- ✓Instant, free and private — every calculation runs client-side in your browser; nothing is uploaded
- ✓Built on the stated formula t = (V/(Q·η)) · ln(C₀/C_t) with authoritative sources cited on the page (McPherson, M.J., Subsurface Ventilation and Environmental Engineering; MSHA 30 CFR Parts 57/75 — Ventilation standards)
- ✓The logarithmic decay model (perfect mixing) sets the FLOOR for re-entry time — stratified fume in long headings clears slower than the math.
- ✓SI ⇄ Imperial toggle converts your inputs in place, so you can work in the units your drawings use
Frequently asked questions
What formula does the blast fume clearance time use?+
It evaluates t = (V/(Q·η)) · ln(C₀/C_t), exactly as published. Sources: McPherson, M.J., Subsurface Ventilation and Environmental Engineering; MSHA 30 CFR Parts 57/75 — Ventilation standards. The substituted worked example on the page lets you verify every step against the textbook.
How should I read the result — and how far can I trust it?+
The logarithmic decay model (perfect mixing) sets the FLOOR for re-entry time — stratified fume in long headings clears slower than the math. Mine ventilation is statutory and life-safety territory: airflow quantities, gas limits and re-entry times must be set by the registered ventilation engineer/manager under your jurisdiction's mining regulations — this calculator is a planning and training aid.
When is this calculator the right tool for the job?+
Re-entry time for a blasted heading from airway volume, airflow and the dilution ratio (perfect-mixing model). A free mine ventilation & air quality tool. Most codes demand both a calculated time and a tested gas reading at re-entry; this calculator provides the first number and the discipline for the second. For neighbouring scenarios, the related tools below cover the same engine with different presets.
Does it support both metric and imperial units?+
Yes — the SI ⇄ Imperial toggle converts the values already in the fields, preserving the physical quantity, so you can flip mid-calculation without re-entering anything.
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