Dust

General

While tunneling, the process of breaking rocks and concrete spraying linings accounts for the most dust generation.

The spread of dust should be suppressed at the source as far as it's possible and should be controlled by methods, such as water infusion, water spraying, and extraction ventilation. When dust is mixed with air, e.g., coal dust, it creates a potential for explosion, and any electrical apparatus present should conform in accordance with CAN/CSA-C22.2 NO. 61241-4:12 (BS 6264: 16.1).

MUST KNOW

According to the Alberta Occupational Health and Safety Code (current as of January 1, 2019) an employer must follow the following:

According to Part 4, Section 28

An employer must

(a) minimize the release of asbestos, silica, coal dust and lead into the air as far as is reasonably practicable,

(b) keep the work site clear of unnecessary accumulations of asbestos, silica, coal dust and lead and waste materials containing any of these substances, and

(c) ensure that the methods used to decontaminate the work area, workers, equipment and protective clothing prevent, as much as is reasonably practicable, the generation of airborne asbestos, silica, coal dust or lead.

According to Part 26, Section 386(c)

AOHS Part 26 (Ventilation Systems) applies to work sites if a mechanical ventilation system controls worker exposure to potentially hazardous dust, fumes, gas, mist, aerosol, smoke, vapour or other particulate of a kind or quantity that is given off by a process.

Sources of Dust

General

There are many processes during the construction of a tunnel that contributes to the generation of dust, among the principal we found:

Drilling and breaking of rocks were dust production is intermittent. On the other hand, machine excavation produces dust constantly. The loading and transport of materials produce further dust (BS 6164: 16.2.2).

Asbestos

Lining materials containing asbestos have been used in tunnels until the early 1980s. If these materials are found while working, possibly in maintenance activities, they should be removed by certified specialized personnel (BS 6164: 16.2.2).

MUST KNOW

According to Alberta OHS Code Part 4, Section 37(1)

An employer must ensure that a worker who works with asbestos receives the training necessary for the worker to perform the work safely.

Effects of Dust

Physical Effects

There are two major physical effects caused by the presence of dust:

• • reduced visibility that increases the risk of accident in moving machinery, and

  • additional wear and tear on plant and equipment.

When there is airborne coal dust, stone dust barriers should be installed where coal is deposited (BS 6164: 16.3.1).

Physiological Effects

The exposure to different kinds of mineral dust can be the cause of chronic lung conditions, where pneumoconiosis is among the most serious. Silica dust and asbestos are among the minerals where special considerations should be taken (BS 6164: 16.3.2).

Occupational Exposure Standards

The exposure of any person to airborne dust should not exceed the exposure limits set by the OHS standards.

Recommended limits for any dust including dust with up to 1% crystalline silica, should be a maximum of 5mg/m3. However, the long-term maximum exposure limit (MEL) for respirable crystalline silica dust should be 0.1 mg/m3(BS 6164: 16.3.3).

MUST KNOW

According to the Alberta Occupational Health and Safety Code (current as of January 1, 2019) Schedule 1:

Exposure limits for Silica-crystalline is 0.025 mg/ m3 (8 hour occupational exposure limit)

Sampling

Exposure should be monitored individually over a specified period by personal samplers. At the time of blasting, air dust conditions are likely to be unacceptable and no worker should be allowed to return to the site until the levels of airborne dust and contaminants have fallen to acceptable levels (BS 6164: 16.4).

Control and Dust Removal

In order to suppress dust and keep it down to optimum levels, high-pressure water jets should be used at the point of rock fracture. These jets may not reduce respirable dust to optimum levels, so monitoring should be kept.

When drilling, the use of hollow bits with water feed can greatly reduce dust generation. Respirable dust cannot be controlled by water sprays, and hence it is important to prevent it from becoming airborne.

An essential part of dust control is the use of extraction, ventilation, and potential filtration. These extract points should be located close to the face of the tunnel.

When calculating the air velocity at any section of the tunnel, it should not be less than 0.5 m/s. This will prevent dust particles from migrating back into the tunnel.  Also, the efficiency of the ventilation system should be tested periodically (BS 6164: 16.5).

Respiratory Equipment

Respiratory protective equipment (RPE) should only be used as a last resort where, for short periods of time, the main control measures cannot keep the dust levels within the optimum range. RPE is not designed to be used as permanent protection.

Proper RPE should be used in accordance with the manufacturer's instructions for storage, maintenance, and training (BS 6164: 16.6).

MUST KNOW

Alberta Occupational Health and Safety Code Relevant to the Topic

As according to the Alberta Occupational Health and Safety Code (current as of January 1, 2019) an employer must follow the following:

According to Part 4, Section 29(2)

An employer must post signs that clearly indicate that

(a) asbestos, silica, coal dust or lead are present in the area,

(b) only authorized persons may enter the area, and

(c) eating, drinking and smoking are prohibited in the area.

According to Part 4, Section 29(4)

An employer must

(a) provide workers in a restricted area with protective clothing that protects other clothing worn by the worker from contamination by asbestos, silica, coal dust or lead,

(b) ensure that workers’ street clothing is not contaminated by asbestos, silica, coal dust or lead, and

(c) ensure that a worker does not leave a restricted area until the worker has been decontaminated.

According to Part 4, Section 29(5)

Alberta OHS Code Part 4, Section 29(4) does not apply in an emergency if the health or safety of a worker requires the worker to leave a restricted area without being decontaminated.

According to Part 4, Section 33

A person must not use asbestos in an air distribution system or equipment in a form in which, or in a location where, asbestos fibres could enter the air supply or return air systems.

According to Part 4, Section 36(1)

An employer who is responsible for removing or abating asbestos or for demolishing or renovating a building or equipment containing asbestos must notify a Director of Inspection of the activity at least 72 hours before beginning the activities that may release asbestos fibres.

According to Part 4, Section 36(2)

A person must not remove or abate asbestos or demolish or renovate a building or equipment containing asbestos if a Director of Inspection has not been notified in accordance with AOHS Part 4: 36(1).

According to Part 4, Section 38(1)

An employer must ensure that asbestos waste is stored, transported and disposed of in sealed containers that are impervious to asbestos and asbestos waste.

According to Part 4, Section 38(2)

An employer must ensure that a container of an asbestos product and asbestos waste is clearly labelled

(a) to identify the contents as an asbestos product and carcinogenic, and

(b) to warn handlers that dust from the contents should not be inhaled.

According to Part 4, Section 40(2)

A health assessment of the worker must include the following:

(a) the identity of the worker and the employer;

(b) the date of the medical examination, chest x-ray and spirogram;

(c) 35 centimetres by 43 centimetres postero-anterior view chest x-ray, including a radiologist’s report;

(d) a spirogram, conducted by a pulmonary function technician, including determinations of forced expiratory volume in the first, second and forced vital capacity;

(e) a history covering

     (i) occupational exposures to asbestos, silica, coal dust or other industrial dusts and carcinogens,

     (ii) significant exposures to asbestos, silica, coal dust, other dust and carcinogens during non work-related activities,

     (iii) significant symptoms that may indicate silicosis, pneumoconiosis, asbestosis or cancer,

     (iv) past and current medical diagnoses of respiratory disease, and

     (v) the worker’s smoking history,

    (f) a written interpretation and explanation of the results of the assessment by a physician, with particular reference to the worker’s exposure to airborne substances.

According to Part 4, Section 40(3)

The physician must give the written interpretation and explanation of the results of the health assessment to the worker not more than 60 days after the tests are completed.

According to Part 4, Section 40(4)

The physician must ensure that the records of the health assessment are kept for not less than 30 years.

According to Part 4, Section 40(6)

An employer must ensure that a worker undergoes a health assessment

(a) not more than 30 calendar days after the worker becomes an exposed worker, and

(b) every two years after the first health assessment.

According to Part 4, Section 40(7)

If an exposed worker received a health assessment from a previous employer within the immediately preceding two years, the worker must inform the present employer of the date or approximate date of that health assessment at the earliest possible time.

According to Part 4, Section 40(8)

An employer must ensure that an exposed worker has received a health assessment within the immediately preceding two years.

Here are some practices from mining specified in the AOHS and relevant to tunneling:

According to Part 36, Section 532

An employer must ensure that a processing plant, other facility or building at a mine is

(a) kept as free as is reasonably practicable of dust, and

(b) cleaned often enough to prevent any dust from becoming a health or safety hazard.

According to Part 36, Section 537(1)

An employer must ensure that if a blast hole drill, rotary drill or other drill is used, the dust released is controlled.

According to Part 36, Section 544(1)

An employer must notify the Director as soon as possible if any of the following occur:

(a) an unexpected major ground fall or subsidence that endangers or may endanger workers, equipment or facilities;

(b) an unplanned stoppage of the main underground ventilation system, if it lasts more than 30 minutes;

(c) a vehicle that goes out of control;

(d) ignition of flammable gas, combustible dust or other material underground;

(e) workers are withdrawn from a hazardous location under emergency conditions;

(f) electrical equipment failures or incidents that cause, or threaten to cause, injury to workers or damage to equipment or facilities;

(g) any other unusual incident or unexpected event that could have caused serious injury to a worker;

(h) outbursts and inrushes; or

(i) an incident involving a hoist, sheave, hoisting rope, shaft conveyance, shaft, shaft timbering or headframe structure.

According to Part 36, Section 544(2)

An employer must notify the Director as soon as possible if any of the following occur and the integrity of a dam or dike is affected:

(a) cracking or evidence of weakening or subsidence of a dam or impoundment dike;

(b) unexpected seepage or the appearance of springs on the outer face of a dam or dike;

(c) the freeboard of a dam or dike is less than adequate; or

(d) there is a washout or significant erosion to a dam or dike.

According to Part 36, Section 548(1)

An employer at an underground coal mine must ensure that

(a) not more than 700 litres of flammable liquid is stored in the mine unless the flammable liquid is stored in a fireproof receptacle or chamber,

(b) mine material likely to cause a fire does not accumulate in any working part of the mine,

(c) mine material likely to cause a fire is kept in fireproof containers that are removed and disposed of at regular intervals,

(d) flammable construction material is not used in an area of the mine in which stationary compressors or other stationary equipment capable of producing more than 400 kilowatts is installed,

(e) tarred or other building paper is not used in the mine, and

(f) propane is not used in the mine except in mine heaters in portal structures.

According to Part 36, Section 548(2)

An employer at an underground coal mine must ensure that the following are constructed of non-flammable material or treated to make them fire resistant:

(a) underground portals;

(b) main fan installations;

(c) booster fan installations;

(d) ventilation air crossings;

(e) stoppings, regulators and doors.

According to Part 36, Section 548(3)

An employer at an underground coal mine must ensure that workers use dust-suppression devices if concentrations of dust may be hazardous.

According to Part 36, Section 548(4)

An employer at an underground coal mine must ensure that unattended conveyor belt transfer points have automatic fire warning devices that sound an alarm in the manned surface control room.

According to Part 36, Section 548(5)

An employer at an underground coal mine must ensure that equipment brought into the mine by workers uses fire resistant hydraulic fluids that meet the requirements of CSA Standard CAN/CSA-M423-M87 (R2007), Fire-Resistant Hydraulic Fluids.

According to Part 36, Section 548(6)

Alberta OHS Code Part 36, Section 548(5) does not apply to the following vehicle components:

(a) axles;

(b) fluid couplings;

(c) braking systems that employ totally enclosed friction elements immersed in a cooling liquid; or

(d) braking systems whose hydraulics are independent of any other hydraulic system

According to Part 36, Section 548(7)

Despite AOHS Part 36: 548(5) and (6), a vehicle that uses an automatic fire suppression system and associated automatic engine shutdown may be approved by the Director if the mine uses a continuous fire detection and gas monitoring system.

According to Part 36, Section 563(1)

An employer must ensure that all electrical equipment in a hazardous location on the surface is approved by the manufacturer or a professional engineer for use in the presence of the specific gas, vapour or dust that is or may be in the location.

According to Part 36, Section 601(1)

An employer must ensure that, in hazardous locations, no combustible dust accumulates at or near the conveyor belt, the belt support rollers, the conveyor belt drive and tail or the belt take-up drums.

According to Part 36, Section 601(2)

An employer must ensure that, if dust may be a hazard, a belt conveyor discharge is constructed so that the amount of dust spilled or dispersed into the air is minimized or eliminated.

According to Part 36, Section 711(1)

An employer must ensure that a mine has a mechanical ventilation system, certified by a professional engineer, that

(a) dilutes, displaces, eliminates or otherwise renders harmless all noxious or flammable gases and harmful substances,

(b) keeps work areas and accessible roads fit for workers to work or travel in,

(c) ensures that the air contains at least 19.5 percent oxygen by volume and not more than 0.5 percent carbon dioxide by volume, and

(d) ensures that a minimum volume of 1.9 cubic metres per second of air passes active working headings.

According to Part 36, Section 711(2)

An employer must develop safe operating procedures for the ventilation system that are certified by a professional engineer.

According to Part 36, Section 711(3)

An employer must ensure that

(a) the ventilation system is designed to prevent the raising of dust, and

(b) compressed air is not used for ventilation.

According to Part 36, Section 742(1)

An employer must ensure that there is a water supply designed to suppress airborne dust

(a) at a location where mineral is transferred from one conveyor to another conveyor, a chute or a vehicle, and

(b) at the cutting teeth or picks of a coal cutting machine

According to Part 36, Section 742(2)

AOHS Part 36: 742(1) does not apply to a location where mineral is conveyed from the conveyor of a mobile unit.

According to Part 36, Section 742(3)

An employer must ensure that a roadway used by rubber-tired vehicles is treated or wetted to minimize the creation of airborne dust.

According to Part 36, Section 742(4)

An employer must ensure that there is an ongoing program for monitoring the concentration of respirable dust to which workers are exposed.

According to Part 36, Section 742(5)

The Director may require an employer to install dust collection devices on exhaust fans if the Director considers that conditions warrant doing so.