Silica Dust Control Case Study: How a Sand‑Molding Foundry Reduced Respirable Silica with Dry‑Fog + Real‑Time PM Monitoring

When you run a high-throughput molding line, silica dust is part of the job—but it doesn’t have to be part of the air your team breathes. In this silica dust control case study, we show how an anonymized West Coast metal casting facility using sand molds implemented a Smart Fog dry-fog system with built-in PM1/PM2.5/PM10 air-quality sensors to slash airborne particulates, document performance in real time, and maintain compliance with the crystalline silica exposure limits referenced in their industrial hygiene report.

You’ll see the baseline exposure picture, the dry-fog design we proposed, why droplet size is the difference-maker, and how closed-loop monitoring takes guesswork out of environmental control. By the end, you’ll have a clear blueprint you can adapt to your own operation.

At-a-Glance Results and Objectives

• Industry: Metal casting (sand molding line)
• Challenge: Elevated respirable crystalline silica from sand handling and mold shakeout; multiple species detected (quartz, cristobalite, tridymite).
• Baseline (personal sample at molding line):
  • Respirable dust (total): 0.51 mg/m³ (10.2% of PEL)
  • Respirable quartz: 14.5 µg/m³ (29% of PEL)
  • Respirable cristobalite: 9.2 µg/m³ (18.4% of PEL)
  • Respirable tridymite: 36.9 µg/m³ (73.8% of PEL)
  • Respirable crystalline silica (reported total): 14.5 µg/m³ (29% of PEL)
  • (Sampling performed with cyclone and 3-stage PVC filter on the Hunter molding line; reference limits from the customer’s report based on Cal/OSHA Table AC-1 at 0.05 mg/m³ / 50 µg/m³.)
• Solution: Smart Fog dry-fog dust suppression around molding, shakeout, and sand conveying + on-site PM1/PM2.5/PM10 sensors for continuous verification.
• Goals: Reduce ambient respirable silica; minimize visible dust; maintain worker exposures comfortably below the action level; generate auditable data to demonstrate control effectiveness.

1) Background: The Exposure Profile in Sand-Molding Operations

Where the dust comes from. Even with good housekeeping, sand casting produces respirable particulate during mold making, shakeout, sand reclamation, and transport. Thermal transformation can create other silica polymorphs (e.g., cristobalite and tridymite) besides quartz, and these respirable particles (typically <10 μm) stay airborne long enough to travel beyond source points.

What the baseline showed. In the anonymized facility, personal sampling captured the mix: quartz, cristobalite, and tridymite (peaking at ~74% of PEL). While still within the reported limit, the combination of multiple species close to thresholds—and the process variability that comes with production peaks—made a strong case for engineering controls beyond PPE and routine ventilation. The operations team wanted a solution that would:

1. Capture fine particles without wetting molds, floors, or electricals.
2. Work continuously with little maintenance or clogging.
3. Prove effectiveness day-to-day with real-time PM data rather than sporadic samples.

Why Smart Fog beat other options. Baghouses and big duct projects carry capital and footprint realities; water sprays can over-wet; misting with larger droplets often misses the finest dust. The team pursued Smart Fog dry-fog humidification to precisely target respirable fractions while keeping the work area dry and safe.

Takeaway: Know your baseline—what species, which tasks, what peaks—then pick a control that matches particle size, process rhythm, and proof requirements.

2) How Dry-Fog Works—and Why Droplet Size Wins at Silica Dust Control

Silica dust control succeeds or fails on the physics of collision and capture. To pull respirable silica (PM10 and below, especially the PM2.5 range) out of the airstream, your water droplets must be similar in size to the particles you’re targeting. If droplets are too large, the finest particles slip around them in the airflow.

Smart Fog engineering:

• Produces a dense cloud of ultra-fine droplets (≈4.2 μm mean diameter) using water + compressed-air powered—small enough to meet airborne silica where it lives.
• Forms billions of collision opportunities per cubic foot. The droplets attach to particles through inertial impaction, interception, and Brownian motion, creating heavier agglomerates that settle rapidly.
• Evaporates as it works. By design, droplets evaporate before reaching surfaces, so you get dust suppression without wetted floors, molds, or cables.
• Uses large orifices relative to droplet size and a unique atomization approach that resists clogging in dusty, mineral-rich environments.

Where it fits. In this project, dry-fog headers surround the molding and shakeout envelope and “flood” the breathing zone during dust-generating sequences. Supplemental nozzles treat transfer points on sand conveyors and any open hoppers. The fog stays where the dust is, not 30 feet up at a ceiling duct.

Actionable takeaway: For silica dust control in foundries, match droplet size to dust size. Sub-10 μm droplets (≈4 μm for Smart Fog) are the sweet spot for PM2.5/PM10 suppression—without over-wetting your process.

3) Design: Coverage, Airflow, and Controls That Fit a Live Molding Line

Map the sources. We started with a dust map of the molding loop: sand mixing, mold forming, core setting, transfer, shakeout, and reclamation. Each zone received one of three approaches:

1. Perimeter fogging: Low-profile stainless headers form a light, even curtain at the breathing zone where operators stand.
2. Point-source fogging: Tuned nozzles at known plume points (e.g., chute drops, belt transitions) for immediate agglomeration.
3. Ambient top-off: Wider-area fogging in the general bay to capture residual drift during peak shifts.

Work with—not against—ventilation. Dry fog pairs best with balanced airflow. We coordinated nozzle orientation with existing local exhaust and general dilution ventilation so fog intersects dust before exhaust capture. Make-up air was positioned to avoid blasting fog away from the target, and the control system sequences fogging with line activity to minimize waste.

No downtime design. The system runs on compressed air and filtered plant water. Modular skids, corrosion-resistant components, and easy-service filters keep maintenance light. Operators control zones from the HMI: Auto (demand-based), Manual, Bypass. A failsafe prevents over-humidification in sensitive areas.

Actionable takeaway: Treat fogging as part of your airflow strategy. Build a zone map, integrate with LEV, and sequence fog to the process—not the other way around.

4) Proof, Not Promises: Real-Time PM1/PM2.5/PM10 Monitoring Built In

You shouldn’t have to wait weeks for a lab report to know whether your silica dust control setup is working. That’s why this installation includes real-time air-quality sensors as part of the system—not an add-on.

What we monitor:

• PM1 for ultra-fine behavior trends that often correlate with the smallest respirable fractions.
• PM2.5 and PM10 to track respirable and thoracic fractions in real time.
• Optional T/RH (temperature/relative humidity) to confirm conditions for optimum fog performance and comfortable work areas.
• Event markers pulled from the line (e.g., “shakeout start”) to correlate process events with PM spikes.

How we use the data:

• Closed-loop control: When PM rises above a programmable threshold, fogging density increases in that zone. When PM stabilizes, the system returns to baseline.
• Dashboards and alerts: Supervisors get live dashboards (line screens and browser view) plus alerting for unusual excursions, so you can act within minutes, not after the shift.
• Compliance evidence: Download time-stamped PM trendlines to show reductions in peaks/exceedances and demonstrate day-to-day control. This supplements—not replaces—your scheduled personal sampling.

Why this matters: You’re not just buying equipment—you’re buying proof. The combination of engineered fog + sensors takes the guesswork out of dust mitigation, gives your EHS team confidence, and makes it simple for management to see ROI in fewer excursions, cleaner air, and steadier productivity.

Actionable takeaway: Require integrated PM1/PM2.5/PM10 monitoring with any dust control project; use thresholds, alerts, and reports to keep the system honest and continuously optimized.

5) Compliance & Risk Reduction: Turning Baseline Data into a Safer Buffer

The facility’s report referenced a crystalline silica limit of 0.05 mg/m³ (50 μg/m³) and highlighted a tridymite result at ~74% of that value—too close for comfort when production surges. The strategy here creates layers of protection:

1. Engineering control (dry-fog): Cut the airborne burden at the source and in the breathing zone.
2. Ventilation synergy: Use LEV/dilution to carry agglomerated particles out of circulation.
3. Monitoring + response: Prevent spikes from turning into sustained excursions with demand-based fogging.
4. Housekeeping & work practice: Keep settled dust from re-entraining and standardize tasks that tend to “dust more.”

What “good” looks like:

• Fewer and smaller PM2.5/PM10 excursions during known dusty tasks.
• Lower area concentrations between tasks (cleaner background).
• Personal samples that stay comfortably below the action level with margin—even on busy days.

Actionable takeaway: Build a buffer—don’t aim to “just meet” the limit. Engineering control + real-time PM1/PM2.5/PM10 monitoring gives you the margin that compliance and worker health deserve.

6) Operations Impact: Safety, Quality, and Cost You Can Feel on the Floor

Beyond compliance, plants feel the benefits of silica dust control everywhere:

• People & Safety: Cleaner air means less coughing, eye irritation, and fatigue. Visibility improves because fog knocks down the haze without making a visual “mist wall.”
• Housekeeping: Less dust settling on equipment and walkways; cleaning goes faster with fewer re-entrainment events.
• Product & Process: No water droplets on molds or sand—dry-fog evaporates as it works—so you avoid material swell, surface defects, or electrical concerns.
• Maintenance: Large-orifice, non-clogging atomizers and no moving parts inside the fogger mean low upkeep.
• Utilities: Systems are engineered for low water and energy use relative to traditional sprays or heavy air movers.
• Proof of value: With PM dashboards and archived reports, you can quantify improvements, justify the investment, and standardize best practices across lines or sites.

Actionable takeaway: Treat dust control as an operational upgrade—your teams will feel the difference, and your metrics will show it.

Implementation Roadmap: From Assessment to Verified Performance

1. Baseline & Goal-Setting
   • Collect/confirm your personal and area samples; identify worst-case tasks.
   • Define target KPIs (e.g., % reduction in PM2.5 peak events, acceptable background PM between tasks, alarm thresholds).
2. Design & Engineering
   • Zone mapping of sources and operator positions.
   • Nozzle layout: perimeter, point-source, and ambient coverage where appropriate.
   • Sequence logic matched to line operations (shakeout, transfer, etc.).
   • Integration with existing LEV and building air patterns.
3. Install & Commission
   • Modular skid placement with water filtration and compressed air tie-in.
   • Fog density tuning by zone; verify no wetting on equipment or molds.
   • Calibrate PM1/PM2.5/PM10 sensors and verify baseline readings.
4. Prove-Out Phase (2–4 weeks)
   • Run in Auto (demand-based).
   • Track PM excursions vs. events; adjust thresholds for responsiveness.
   • Capture before/after comparisons during like-for-like production.
5. Operate, Document, Improve
   • Weekly PM reports; exception alerts.
   • Quarterly nozzle/no-load checks; water filter swaps per schedule.
   • Fold results into EHS reviews and continuous improvement.

Comparison: Dry-Fog vs. Other Dust Controls

Best practice: Pair dry-fog with LEV where feasible; fog reduces the ambient load while LEV focuses on source capture. The PM sensors show you how the combo performs day-to-day.

Frequently Asked Questions

Q1: Will fog make the sand or molds wet?
A: No. Smart Fog self-evaporating droplets evaporate as they work, so they bind dust in the air without wetting surfaces. The system is tuned to avoid condensation even in cooler spots.

Q2: Can the system keep up with variable production?
A: Yes. We use demand-based control: when PM2.5/PM10 rises in a zone, fog density steps up automatically; when levels stabilize, it returns to baseline. You get performance only when and where it’s needed.

Q3: How do you prove it’s working?
A: With integrated PM1/PM2.5/PM10 sensors and dashboards. You’ll see fewer, smaller excursions during dusty tasks and cleaner background levels between cycles. Periodic personal samples confirm results.

Q4: What about maintenance?
A: Routine checks are light: water filtration, inspection of headers, and scheduled service. Atomizers are built to resist clogging and run reliably in dusty environments.

Q5: Do we still need ventilation and PPE?
A: Dry-fog is an engineering control that reduces airborne burden, but it should complement LEV/dilution and administrative controls. PPE policies remain as your EHS program dictates.

Q6: Is this only for silica?
A: No. Dry-fog agglomerates a wide range of respirable dusts (metal fines, sand fines, additives). Silica is a flagship use case because of its health risk and regulatory attention.

How to Apply This Blueprint to Your Plant

1. Gather your latest air sampling data (species and concentrations by task).
2. Ask for a zone-by-zone fog layout: perimeter, point-source, ambient.
3. Include PM sensors in the scope—don’t bolt them on later.
4. Integrate with your airflow (LEV and make-up air) so fog intersects dust before capture.
5. Define acceptance criteria in advance (e.g., “≤X PM2.5 excursions per shift over Y μg/m³ for >Z minutes”).
6. Run a prove-out period and adopt demand-based thresholds that fit your actual production rhythm.

Conclusion: Safer Air, Less Guesswork—That’s Silica Dust Control You Can Prove

Silica dust control in a sand-molding foundry doesn’t have to be a tug-of-war between compliance, comfort, and production. With Smart Fog dry-fog humidification, you match droplet size to dust size to capture what actually threatens workers’ lungs—respirable crystalline silica. And with integrated PM1/PM2.5/PM10 sensors, you don’t just hope it’s working—you see it working, minute by minute, shift after shift.

For the anonymized facility in this case study, the program turns a solid but tight baseline into a durable safety buffer, shrinking PM spikes around molding and shakeout while keeping the process dry and reliable. The result is cleaner air, clearer visibility, and the confidence that comes from proof, not promises.

Ready to explore a design for your line?
Talk with our engineers about a zone-mapped silica dust control plan with built-in PM monitoring tailored to your molding and shakeout sequence. We’ll help you turn your sampling report into a practical, data-driven solution—so your team can breathe easier while production keeps moving.

Want the full technical brief or a live demo of the PM dashboard? Contact us to schedule a virtual walkthrough of Smart Fog for your foundry.