Underground Auxiliary Ventilation
How much air a development heading needs, what it costs in pressure to push
that down a duct, and what the fan burns in electricity to do it.
Auxiliary ventilation of a single dead-end heading only: one fan, one
duct, one face. It is not a mine ventilation network model, it does not balance a circuit or
solve for splits, it is not a heat or refrigeration calculation, and it is not a gas monitoring
plan. Statutory airflow is set by your regulator and your ventilation officer, not by this page.
Step 1: The heading
The opening sets the velocity you can get away with.
Step 2: What has to be diluted
Diesel almost always sets the number. Velocity limits then check it.
Step 3: The duct
Diameter is the whole game. Resistance goes as area cubed.
Step 4: Running it
Air power goes as the cube of airflow. Doubling the air costs eight times.
| Step | Value | Where it comes from |
|---|
The heading and the duct
Where the pressure goes
Friction factors, by what the air is running through
| Type of airway or ducting | Friction factor k, kg/m³ |
|---|---|
| Ventilation ducting | |
| Collapsible fabric ducting (forcing systems only) | 0.0037 |
| Flexible ducting with fully stretched spiral reinforcement | 0.011 |
| Fiberglass | 0.0024 |
| Spiral-wound galvanized steel | 0.0021 |
| Rectangular airways | |
| Smooth concrete lined | 0.004 |
| Shotcrete | 0.0055 |
| Unlined with minor irregularities only | 0.009 |
| Girders on masonry or concrete walls | 0.0095 |
| Unlined, typical conditions, no major irregularities | 0.012 |
| Unlined, irregular sides | 0.014 |
| Unlined, rough or irregular conditions | 0.016 |
| Girders on side props | 0.019 |
| Drift with rough sides, stepped floor, handrails | 0.04 |
| Steel arched airways | |
| Smooth concrete all round | 0.004 |
| Bricked between arches all round | 0.006 |
| Concrete slabs or timber lagging between flanges all round | 0.0075 |
| Slabs or timber lagging between flanges to spring | 0.009 |
| Lagged behind arches | 0.012 |
| Arches poorly aligned, rough conditions | 0.016 |
| Shafts | |
| Smooth lined, unobstructed | 0.003 |
| Brick lined, unobstructed | 0.004 |
| Concrete lined, rope guides, pipe fittings | 0.0065 |
| Brick lined, rope guides, pipe fittings | 0.0075 |
| Unlined, well-trimmed surface | 0.01 |
| Unlined, major irregularities removed | 0.012 |
| Unlined, mesh bolted | 0.014 |
| Brick lined, two side buntons | 0.018 |
| Two side buntons each with a tie girder | 0.022 |
| Longwall face | |
| Good conditions, smooth wall | 0.035 |
| Typical conditions, coal on conveyor | 0.05 |
| Rough conditions, uneven faceline | 0.065 |
SME Mining Engineering Handbook, Table 15.3-1, p. 1579,
from McPherson 1993, referred to an air density of 1.2 kg/m³. Only the ventilation ducting
rows drive this page; the airway rows are shown because an auxiliary duct discharges into an
airway and it is worth seeing what the same air costs in each.
This table came back flagged as “rows 37 vs claimed 32”. Rendering p. 1579 and
counting settles it: 32 data rows plus five section headings is 37, and all 37 were transcribed.
The count was the model disagreeing with itself, not a row going missing.
What a bend costs in straight duct
| Source of loss | Equivalent length, m | ft |
|---|---|---|
| Entrance loss | 10.7 | 35 |
| Exit loss | 30.5 | 100 |
| Bend (generic), 90° | 10.7 | 35 |
| Bend (generic), 60° | 7.5 | 24.5 |
| Bend (generic), 45° | 5.3 | 17.5 |
| Coupling, spiral-reinforced duct | 2.4 | 8 |
| Lay-flat tubing, coupling | 2 | 6 |
| Lay-flat tubing, 90° bend | 46 | 150 |
SME Mining Reference Handbook, 2nd ed., equivalent lengths
for vent pipe and tubing, p. 362. Published in both meters and feet, and the two agree across
every row, which is a check a transcription cannot pass by accident.
The printed note on entrance and exit is load-bearing and is a question this page asks you
rather than assuming: they are counted only if the fan is not located at the point of
loss. Values given as a multiple of D scale with your duct diameter, and the sharp
against smooth distinction is the bend centerline radius: 0.75D is sharp, 1.25D is smooth.
Velocity and dilution limits
| Area | Maximum velocity, m/s |
|---|---|
| Working faces | 4 |
| Conveyor drifts | 5 |
| Main haulage routes | 6 |
| Smooth-lined airways | 8 |
| Heating shafts | 10 |
| Ventilation shafts | 20 |
| Commonly applied minimum | 0.3 |
SME Mining Engineering Handbook, Table 15.3-2, p. 1590. The same page gives a commonly applied minimum of 0.3 m/s after McPherson 1993, and both ends are checked here.
| Location | Diesel airflow requirement | Comments |
|---|---|---|
| Western Australia | 0.05 m³/s per kW | |
| Queensland, Australia | None | None. Was 0.04 m³/s per kW |
| Ontario, Canada | 0.06 m³/s per kW | |
| Manitoba, Canada | 0.92 m³/s per kW | Uses 100/75/50 rule |
| United Kingdom | None | None |
| United States | 0.032 m³/s per kW | 0.032 to 0.094 m³/s per kW; typically design to 0.08 |
| Chile | 0.063 m³/s per kW | |
| South Africa | None | None. Exhaust/overlap system required for firing anytime; typically design to 0.06 |
| Indonesia | 0.067 m³/s per kW |
SME Mining Engineering Handbook, Table 15.3-3, p. 1590,
after Brake and Nixon 2008. These are regulatory numbers, not physics, which is why they differ
so much between jurisdictions and why some publish none at all.
Manitoba is quoted on a different basis and this page will not let you use it as a
simple multiplier. Its 0.92 m³/s per kW is more than ten times every other
jurisdiction on the list, and the printed comment says why: it “uses 100/75/50
rule”, which apportions the rated power of multiple machines rather than summing it. The
number is faithfully what the page prints. It is not comparable to the others.
Spending more time on spreadsheets than on the job?
We build the reporting and admin automation for mining contractors, so the numbers keep themselves.
Book a 20 min callWorked example
Worked with the values this page loads with, so the method can be checked against the cited source without entering anything. Change any input above and the calculator recomputes; the numbers below stay as a fixed reference case.
- 15.00 m³/s
- 1957 Pa
- $4614
| Heading cross-section | 22.5 m² | width × height |
| Diesel in the heading | 150.0 kW | your input |
| Dilution basis | 0.08 m³/s per kW | United States, the design figure the page names, Table 15.3-3 p. 1590 |
| Airflow for diesel dilution | 12.00 m³/s | rate × kW |
| Airflow for the 0.3 m/s minimum | 6.75 m³/s | 0.3 m/s × heading area, McPherson 1993, p. 1590 |
| = airflow needed at the face | 12.00 m³/s | the larger of the two |
| ÷ (1 − 20% leakage) | 15.00 m³/s | your input; the handbook publishes none |
| Duct diameter | 1000 mm | your input |
| Duct area | 0.785 m² | π d² ÷ 4 |
| Duct perimeter | 3.14 m | π d |
| Friction factor k | 0.0037 | Collapsible fabric ducting (forcing systems only), Table 15.3-1 p. 1579 |
| Straight duct length | 300 m | your input |
| + entrance loss | 11 m | equivalent lengths p. 362 |
| + exit loss | 31 m | equivalent lengths p. 362 |
| + 2 × 90° bend | 21 m | 10.7 m each, equivalent lengths p. 362 |
| + 0 × 45° bend | 0 m | 5.3 m each, 50% of a 90°, equivalent lengths p. 362 |
| = effective length | 363 m | straight + every shock loss as equivalent duct |
| Resistance R | 8.6998 N·s²/m⁸ | R = k L per ÷ A³, p. 1579 |
| = fan pressure | 1957 Pa | p = R Q², the square law, p. 1579 |
| of which straight duct | 1620 Pa | the 300 m of real duct |
| of which bends and ends | 338 Pa | the 63 m of equivalent duct |
| Air velocity in the duct | 19.10 m/s | fan airflow ÷ duct area |
| Air velocity across the heading | 0.53 m/s | face airflow ÷ heading area; 4 m/s max at working faces, Table 15.3-2 p. 1590 |
| = air power | 29.4 kW | p × Q, p. 1579 |
| ÷ 65% fan and drive efficiency | 45.2 kW | your input |
| = electricity per month | $4614 | 24 h/day × 30.4 days × $0.14/kWh |
Estimating aid only. This is not an engineering design and not a substitute for the judgment of a competent or qualified person. Verify every result against the cited source and your own site conditions. Full terms and disclaimer.