Dry Grinding Overlay Removal Near a Storm Drain

Immediate action: stop the dry grinding and move the crew out of the dust plume. The visible plume and the worker's cough indicate a likely overexposure to respirable crystalline silica, so continuing for the sake of schedule is not defensible.

Control hierarchy, in order:

• Elimination/substitution: use wet grinding or a grinder with a HEPA vacuum shroud. These are the primary controls because they keep dust from becoming airborne. Water must be controlled so runoff does not reach the storm drain.
• Engineering controls: if wet or vacuum methods are not feasible, isolate the work with enclosures and negative-pressure HEPA filtration. General ventilation alone is not adequate outdoors in a 25 km/h wind because the plume is unpredictable.
• Administrative controls: establish an exclusion zone, restrict access, and schedule work to reduce the number of workers exposed.
• PPE: fit-tested, appropriate respirators are the last line of defence, not the main control. A dust mask is not adequate for silica.

A written silica exposure control plan, air monitoring where required, and training must be in place before restarting. The worker with symptoms should be removed from exposure and referred for medical evaluation; the episode should be recorded.

The storm drain is the key constraint because it is a direct, untreated pathway to the receiving water. Washout water is highly alkaline, contains suspended solids, and may carry admixtures and trace metals. Allowing chute or drum washout to enter the drain would create a prohibited discharge regardless of how small the volume appears.

A lined, bermed washout pit should be located at least 15-20 m from the drain and outside any overland flow path. The pit should be sized for the expected volume from three trucks, with enough freeboard for a rain event. Practical measures:

• Line the pit with an impermeable liner and berm it to contain splatter.
• Do not pump or decant liquid to the storm drain; allow solids to settle, then test pH and manage the liquid as required by the local authority.
• Remove and dispose of hardened solids at an approved facility.
• Keep a spill kit and absorbent material at the washout station.

The reasoning is that containment must be in place before the trucks arrive, not after a spill. The drain location and the number of trucks determine the pit capacity and the monitoring needed.

The worker should be removed from the silica-exposure area and not allowed to return to dry grinding that shift. A cough and shortness of breath after two hours of visible dust exposure are symptoms that warrant medical evaluation; the supervisor is not qualified to clear the worker. Arrange first aid or transport as needed, and notify the site safety officer and the employer.

The response should include:

• Documenting the exposure conditions: task, duration, controls in use, wind, and visible dust.
• Recording the worker's symptoms and the action taken.
• Arranging medical evaluation and following the medical practitioner's recommendations on return to work.
• Reviewing the incident to determine whether exposure controls failed and whether other workers were affected.
• Retaining records as required by occupational health and safety legislation and the project's health and safety plan.

The reasoning is that symptoms can be delayed and the worker's willingness to continue does not override the employer's duty to protect health. The event is also evidence that the control plan was inadequate, so it must trigger a review rather than a one-off send-home.