Tunnel & Underground Silica SWMS

Tunnel and underground silica work covers excavation, drilling, breaking, shotcreting and spoil handling in tunnels, shafts and underground workings driven through rock and ground that contains crystalline silica. It is among the most serious respirable crystalline silica (RCS) exposures in construction because three factors compound: the rock can be very high in crystalline silica, the work generates dust continuously through drilling and breaking, and the underground environment confines that dust with limited natural ventilation. On top of the silica hazard, the underground setting brings confined space and atmospheric hazards, ground instability and plant interaction. This document is deliberately comprehensive because several regimes apply at once: tunnel work and confined space work as high risk construction work, and high-risk processing of a crystalline silica substance.

The work engages multiple high risk construction work categories under the model Work Health and Safety Regulations — work involving tunnels, and work in or near a confined space and an atmosphere that may be contaminated — each requiring a SWMS prepared before the work commences, kept readily accessible, and given to the principal contractor if one is appointed. Simultaneously, drilling, breaking and processing the silica-bearing rock is processing of a crystalline silica substance, which is high risk where it is reasonably likely to result in a risk to health, the practical trigger being airborne RCS above half the workplace exposure standard generated regularly — a threshold underground silica work readily reaches. The exposure standard is 0.05 mg/m3 as an eight-hour time-weighted average, which must not be exceeded, reframed as a workplace exposure limit from 1 December 2026. Where the work is high-risk silica processing, a silica risk control plan, air monitoring and health monitoring apply in addition to the construction SWMS. This document is written on the basis that engineered ventilation and wet drilling are the primary silica controls underground and that the silica, confined space and tunnel controls operate together.

Hazards identified

10 hazards covered, sorted by priority.

Control measures

Hierarchy-of-controls order: elimination → substitution → isolation → engineering → administrative → PPE.

1. 1Elimination: where the design allows, use methods that reduce dry breaking underground — for example mechanical excavation with integrated suppression over drill-and-blast where ground conditions permit.
2. 2Substitution: select lower-dust drilling and excavation techniques where a choice exists, and use wet shotcrete processes that reduce rebound dust.
3. 3Engineering: forced underground ventilation designed to dilute and remove RCS, diesel particulate and other contaminants and maintain a safe atmosphere, as a primary control specific to the underground environment.
4. 4Engineering: wet drilling with water flushing to the bit, and water suppression at breaking, shotcreting and spoil-handling points, to control RCS at the point of generation.
5. 5Engineering: a ground-support and ground-control system designed by a competent person for the ground conditions, with monitoring of ground behaviour.
6. 6Engineering: low-emission or filtered underground plant to limit diesel particulate matter, maintained to keep exhaust emissions down.
7. 7Administrative: prepare a SWMS before the work commences for the tunnel and confined space high risk construction work, and a silica risk control plan for the high-risk processing of a crystalline silica substance, available at the workplace.
8. 8Administrative: continuous atmospheric monitoring for oxygen, contaminants and flammable gases, and air monitoring for RCS to validate the controls hold below the exposure standard, with exceedances notified to the regulator within the prescribed period.
9. 9Administrative: enrol workers in health monitoring supervised by a registered medical practitioner, including respiratory function testing and low-dose high-resolution chest CT, and retain records confidentially for at least 30 years.
10. 10Administrative: confined space and underground entry controls, plant-and-pedestrian exclusion zones with communication, and a documented emergency response and rescue capability for the underground workings.
11. 11PPE: a fit-tested P2 half-face respirator as the minimum residual control, upgraded to a powered air-purifying respirator for sustained drilling and breaking, selected and maintained per AS/NZS 1715 and AS/NZS 1716; underground atmospheres that may be oxygen-deficient require supplied air, not air-purifying respirators.
12. 12PPE: hearing protection matched to the measured noise level, eye protection to AS/NZS 1337.1, underground high-visibility clothing, gloves, and Class I or Class II safety footwear with protective toecap to AS/NZS 2210.3.
13. 13Administrative: all workers must hold a valid White Card (General Construction Induction Training, CPCCWHS1001) before entering any construction workplace, with additional underground and confined space competencies verified before entry.
14. 14Administrative: conduct a pre-shift toolbox talk covering ventilation status, silica and atmospheric controls, ground conditions, plant movements and emergency procedures, record attendance, manage water and slurry so it does not discharge uncontrolled, and review and update this SWMS whenever the scope changes, after any incident, when a worker or health and safety representative raises a concern, or at minimum every 12 months.

Applicable Codes of Practice

High-Risk Construction Work triggered

Worked example

An underground civil crew is driving a small access tunnel through sandstone with a high crystalline silica content, using drill-and-blast advance and wet shotcrete ground support. The work involves a tunnel and a confined underground atmosphere, so a SWMS is prepared before the work starts for the tunnel and confined space high risk construction work, and because drilling and breaking the silica-rich rock generates respirable crystalline silica continuously it is also high-risk processing of a crystalline silica substance, so a silica risk control plan is prepared and RCS air monitoring is arranged. Forced ventilation is designed and run to dilute and remove silica dust, diesel particulate and other contaminants and to maintain a safe atmosphere, with continuous atmospheric monitoring for oxygen, contaminants and flammable gases. Drilling is carried out wet with water flushing to the bit, and suppression is applied at the shotcrete and spoil-handling points. Ground support is installed to a competent person's design with ground monitoring, and low-emission plant is used to limit diesel particulate. Crews wear fit-tested P2 respirators, upgrading to powered air-purifying respirators for sustained drilling, with supplied air available for any oxygen-deficient atmosphere. Plant-and-pedestrian separation and an underground emergency and rescue capability are maintained. Personal and area monitoring confirm the controls hold below the exposure standard, the records are retained, and the workers are enrolled in health monitoring with a registered medical practitioner.

Related legislation

• Model Work Health and Safety Act — primary duty of care; the duty to consult workers; the reckless-conduct offence; and notifiable-incident provisions, as enacted in each jurisdiction.
• Model Work Health and Safety Regulations — the high risk construction work provisions for tunnel work and confined space work, the SWMS preparation and review duties, the confined space entry and atmospheric provisions, and the crystalline silica high-risk processing, silica risk control plan, air monitoring and health monitoring provisions, as enacted in each jurisdiction.
• Workplace exposure standard for respirable crystalline silica: 0.05 mg/m3 (eight-hour time-weighted average), which must not be exceeded; reframed as a workplace exposure limit from 1 December 2026.
• Diesel particulate matter and the relevant atmospheric contaminant standards apply to the underground environment in addition to the RCS standard.
• Victoria operates under the Occupational Health and Safety Act 2004 and the Occupational Health and Safety Regulations 2017, with the tunnel, confined space and silica provisions and Compliance Codes applying in place of the model instruments; mining and certain underground works may also engage jurisdiction-specific mines safety legislation.

Frequently asked questions