Capstone: a silica and lead exposure control plan

This capstone brings the course together. You will work through a combined silica and lead exposure control plan for the renovation of an older building, from hazard identification to clearance, and then review a weak draft plan to find its gaps. The building, the company and all figures are invented for the exercise. Treat the result as a model for the kind of thinking a plan needs, not as a template to copy without professional review.

The project

Maple Ridge Community Hall is a two-storey brick building constructed in 1938, with a concrete block addition from 1962 and a steel-framed gymnasium. The owner plans an eight-week renovation while the building is closed. The work includes:

• Removing and replacing 40 original wooden windows and their trim, painted many times since 1938.

• Cutting a new doorway through a 200 mm concrete block wall in the addition.

• Cutting two openings in the original brick walls for new ventilation ducts.

• Chasing grooves in plaster-on-brick walls for new electrical conduit.

• Grinding the concrete floor of the gymnasium before applying a new finish.

• Cutting and removing two painted steel beams in the gymnasium to make way for a mezzanine.

• Daily clean-up and final cleaning before the building reopens to the public, including a daycare program.

Step 1: identify the hazards

Before any planning, the project team commissions a hazardous materials survey. The survey finds lead in the window paint (XRF readings of 2.4 to 9.8 mg/cm²) and in the primer on the gymnasium steel beams (laboratory result 6.1 per cent by weight). The plaster and joint compounds tested negative for asbestos, but the survey recommends stopping work and re-testing if suspect materials are found during demolition, as HSE-246 describes. The brick, block, mortar and concrete are presumed to contain crystalline silica.

Step 2: estimate exposure

With no sampling data for this exact job, the team uses task-based guidance and published data for similar tasks to estimate exposure with and without the planned controls. The estimates are deliberately conservative and will be checked by sampling in the first week.

# Illustrative task exposure estimates (ug/m3, during the task) with and without controls.
tasks = [
    # task, agent, uncontrolled, fraction remaining with controls, hours per day
    ("block doorway, wet walk-behind saw", "silica", 1500, 0.08, 2),
    ("brick openings, wet saw and shrouded chipping", "silica", 1200, 0.12, 3),
    ("wall chasing, shrouded chaser + HEPA vac", "silica", 900, 0.06, 4),
    ("floor grinding, integrated HEPA collector", "silica", 2000, 0.03, 6),
    ("window trim, wet scraping", "lead", 120, 0.25, 6),
    ("steel beams, cold cutting after strip-back", "lead", 3000, 0.02, 3),
]
limits = {"silica": 25, "lead": 50}   # ug/m3 8-h TWA used for this plan

print(f"{'task':46s} {'controlled':>10s} {'8-h TWA':>8s} {'x limit':>8s}")
for task, agent, unc, frac, hrs in tasks:
    controlled = unc * frac
    twa = controlled * hrs / 8          # assume no other exposure that day
    print(f"{task:46s} {controlled:10.0f} {twa:8.1f} {twa / limits[agent]:8.1f}")

task                                           controlled  8-h TWA  x limit
block doorway, wet walk-behind saw                    120     30.0      1.2
brick openings, wet saw and shrouded chipping         144     54.0      2.2
wall chasing, shrouded chaser + HEPA vac               54     27.0      1.1
floor grinding, integrated HEPA collector              60     45.0      1.8
window trim, wet scraping                              30     22.5      0.5
steel beams, cold cutting after strip-back             60     22.5      0.5

Even with good engineering controls, several silica tasks are estimated to remain above the 25 µg/m³ limit used for the plan, and the steel beam removal remains above the lead limit. Respirators will therefore be required for those tasks, and sampling will check the estimates. The plan uses 25 µg/m³ for silica and 50 µg/m³ for lead as its internal limits.

These are the ACGIH values adopted in most provinces. If the project were in Ontario, the legal quartz limit would be higher, but using the lower value gives better protection and is good practice.

Step 3: choose controls task by task

Note how elimination and substitution appear first in several rows: replacing whole windows, eliminating some chasing with surface-mounted conduit and replacing torch cutting with cold cutting each remove large exposures before engineering controls are even considered.

Step 4: hygiene, access and waste

Because both lead and silica are present, the plan sets up hygiene facilities from the first day:

• A decontamination unit at the main work entrance with dirty, shower and clean rooms, used by anyone leaving the steel beam and window zones.

• Hand-wash stations with soap, warm water and paper towels at each zone exit.

• A clean break room in a separate office, entered only after removing coveralls and washing.

• Employer-supplied disposable coveralls and boot covers, bagged as lead waste.

• Work zones marked with signs and barriers; entry limited to trained workers wearing required protection.

• Lead waste (paint chips, sheeting, coveralls, filters) in sealed, labelled bags, stored in a locked outdoor container and tested or disposed of as hazardous waste as required. Silica slurry settled and disposed of with construction waste, never washed into storm drains.

Step 5: monitoring, surveillance and training

Step 6: cost and schedule

Controls cost money and time, and the plan is more likely to be followed if those costs are built into the bid and schedule rather than discovered on site.

# Illustrative cost of the control plan for an 8-week project (currency units)
costs = {
    "HEPA vacuums, shrouds and wet saws (rental)": 9_800,
    "floor grinder with HEPA collector (rental)": 6_500,
    "decontamination unit and hand-wash stations": 7_200,
    "containment materials and signs": 3_400,
    "disposable coveralls, boot covers, filters": 4_100,
    "PAPRs (purchase, reusable)": 5_600,
    "air and wipe sampling with laboratory fees": 6_800,
    "blood lead tests (3 rounds x 6 workers)": 1_350,
    "training and fit testing": 2_900,
    "hazardous waste disposal": 3_700,
}
total = sum(costs.values())
contract = 640_000
for item, c in costs.items():
    print(f"{item:46s} {c:>8,}")
print(f"{'total control cost':46s} {total:>8,}")
print(f"share of an illustrative {contract:,} contract: {total / contract:.1%}")
extra_days = 4
print(f"allowance for set-up, decontamination and clean-up: {extra_days} working days")

HEPA vacuums, shrouds and wet saws (rental)       9,800
floor grinder with HEPA collector (rental)        6,500
decontamination unit and hand-wash stations       7,200
containment materials and signs                   3,400
disposable coveralls, boot covers, filters        4,100
PAPRs (purchase, reusable)                        5,600
air and wipe sampling with laboratory fees        6,800
blood lead tests (3 rounds x 6 workers)           1,350
training and fit testing                          2,900
hazardous waste disposal                          3,700
total control cost                               51,350
share of an illustrative 640,000 contract: 8.0%
allowance for set-up, decontamination and clean-up: 4 working days

In this illustration, the controls cost under a tenth of the contract value. Building that cost into the bid protects workers, protects the children who will use the building afterwards and avoids the much larger costs of stoppages, re-cleaning, claims and penalties.

Reviewing a weak draft plan

Before the plan above was written, a subcontractor submitted the draft below. Reviewing it is good practice for spotting the gaps that appear again and again.