Mine Ventilation

Mine Dust Sampling & Control

Respirable dust, gravimetric sampling and time-weighted exposure — measuring the airborne dust that causes pneumoconiosis and silicosis.

PART 1

Topic Breakdown & Traps

The Engineering Principle

Fine airborne dust — especially the respirable fraction (roughly < 5–7 µm, small enough to reach the alveoli) and crystalline silica — causes the irreversible lung diseases pneumoconiosis and silicosis. Because the hazard is a *dose* (concentration × time), we measure the airborne mass concentration by gravimetric sampling: a personal pump draws air at a known, steady flow rate across a pre-weighed filter; re-weighing the filter gives the mass of dust collected, and dividing by the volume of air sampled gives the concentration. Over a shift, exposure is summarised as a time-weighted average (TWA) so that short high-exposure spells and longer low-exposure spells are combined fairly.

The Core Formula Matrix

Volume of air sampled:

V = Q_{s} t

Q_{s}

= sampling flow rate

[L/min]

t

= duration

[min]

. Convert litres to m³ by dividing by 1000.

Dust concentration (gravimetric):

c = \frac{m}{V} [mg/m^{3}]

m

= mass of dust collected

[mg]

V

= volume sampled

[m^{3}]

.

Time-weighted average over a shift of

n

intervals:

TWA = \frac{\sum c _{i} t _{i}}{\sum t _{i}}

c_{i}

= concentration during interval

i

t_{i}

= its duration.

Gravimetric sampling train: intake → size-selective cyclone (removes coarse dust) → pre-weighed filter → constant-flow pump. Concentration = filter mass gain ÷ (flow × time).

The ‘IIT Traps’

⚠
Litres ↔ cubic metres. $1 m^{3} = 1000 L$ . A pump at 2 L/min for 480 min samples $960 L = 0.96 m^{3}$ , not 960 m³. Forgetting the ÷1000 is the dominant error in dust questions.
⚠
Mass units. Filters gain milligrams; concentration is mg/m³. Mixing mg with g (×1000) throws the answer off by three orders of magnitude.
⚠
TWA is time-weighted, not a plain average. Average the concentrations *weighted by their durations*; a simple mean of the readings is wrong whenever the intervals differ.
⚠
Total vs respirable. The health limit applies to the respirable fraction (after the size-selective cyclone), which is only part of the total airborne dust — comparing total dust to the respirable limit over-reads compliance.

PART 2

Progressive 3-Tier Question Suite

Q1BASIC1 Mark · MCQ

A personal sampler runs at a flow rate of

2.0 L/min

for a full shift of

480 min

. The volume of air sampled is:

Q2MEDIUM2 Marks · NAT

A gravimetric sampler draws air at

1.9 L/min

for

420 min

. The pre-weighed filter gains

2.10 mg

of respirable dust. The mean respirable-dust concentration is ______ mg/m³. (Round off to two decimal places.)

mg/m³

Q3HARD2 Marks · NAT

During an 8-hour shift a miner spends 4 h in a zone measuring

3.0 mg/m^{3}

respirable dust and 4 h in a zone measuring

1.0 mg/m^{3}

. The 8-hour time-weighted-average exposure is ______ mg/m³. (Round off to two decimal places.)

Exposure profile over the shift: 4 h at 3.0 mg/m³ then 4 h at 1.0 mg/m³. The TWA is the duration-weighted mean (dashed line).

mg/m³