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Activity U10M1-001: Media Selection & Hazard Analysis

Activity ID: U10M1-ACT-001 Title: Abrasive Media Selection & Hazard Profile Comparison Duration: 45 minutes Objective: Learners will evaluate five blasting media types, assess their hazard profiles, and recommend appropriate media for specific applications based on material, aesthetic goal, and health/safety considerations.

Key Topics

  • Silica vs. non-silica media properties
  • Dust production and particulate hazard
  • Cost and recyclability considerations
  • Surface finish quality and material interaction
  • Occupational health implications of media choice

Instructions/Procedure

Step 1: Media Sample Examination (10 minutes)

  1. Your instructor has provided five containers of blasting media:
  2. Container A: Crystalline Silica (medium sand, 100–200 microns)
  3. Container B: Glass Beads (soda-lime glass, 75–150 microns)
  4. Container C: Aluminum Oxide (fused, 80–120 grit)
  5. Container D: Steel Shot (hardened steel, various sizes)

  6. Container E: Walnut Shell (organic, 100–300 microns)

  7. Examine each sample visually:

  8. Observe color, size uniformity, particle shape (angular vs. rounded)
  9. Note relative density (containers feel different weights)

  10. Review the printed label for hazard warnings

  11. For each medium, complete the Media Observation Sheet (provided):

  12. Color and appearance
  13. Particle size (visual estimate: fine, medium, coarse)
  14. Particle shape (angular, rounded, irregular)
  15. Density impression (light, medium, heavy)

  16. Hazard symbols visible on label

  17. Do NOT taste, inhale, or ingest any media. If any media is spilled, notify your instructor immediately.

Step 2: Hazard Profile Research (15 minutes)

  1. Working in pairs or small groups, you will be assigned one medium to research in detail:
  2. Pair A: Crystalline Silica
  3. Pair B: Glass Beads
  4. Pair C: Aluminum Oxide
  5. Pair D: Steel Shot

  6. Pair E: Walnut Shell

  7. Using the provided Media Reference Sheets and SDS (Safety Data Sheets), research your assigned medium:

A. Occupational Health Hazard: - What is the primary health concern? (e.g., silicosis for silica, hearing loss for steel shot) - Exposure limits (OSHA PEL, ACGIH TLV) - Latency period (how long before symptoms appear) - Reversibility (is the damage permanent?)

B. Dust & Particulate: - Dust production rate (high, medium, low) - Particle size distribution (respirable vs. non-respirable) - Special hazards (flammability, reactivity, etc.)

C. Environmental Impact: - Recyclability (can it be reused? How many cycles?) - Disposal requirements - Water pollution risk

D. Material Compatibility: - Best suited for: metals, glass, ceramics, composites? - Finish quality: aggressive, medium, gentle? - Any materials it should NOT be used on?

E. Cost & Efficiency: - Relative cost per pound - Coverage rate (how long does a batch last?) - Sustainability

  1. Complete the Hazard Profile Table for your assigned medium (template provided).

Step 3: Application Scenario Analysis (15 minutes)

You will be presented with five application scenarios. For each, you must recommend an appropriate blasting medium and justify your choice based on hazard, material compatibility, and quality/aesthetic goals.

Scenario 1: Removing rust from a mild steel automotive panel - Goal: Clean bare metal before welding repair - Constraint: No residual media contamination allowed - Recommendation: _ - Justification: - Material compatibility: __ - Hazard profile: ___ - Cost/efficiency: _______

Scenario 2: Creating a frosted/etched effect on glass for a decorative signage project - Goal: Aesthetic finish, uniform matte texture - Constraint: Low cost, minimal health hazard - Recommendation: _ - Justification: - Finish quality: __ - Safety: ___ - Cost: _______

Scenario 3: Removing paint from a wooden sculpture (fine detail work) - Goal: Preserve wood detail; remove paint without damaging underlying surface - Constraint: Organic material; cannot withstand aggressive blasting - Recommendation: _ - Justification: - Material sensitivity: __ - Control/precision: ___ - Environmental impact: _______

Scenario 4: Industrial cleaning of heavy machinery (large metal parts, oil/corrosion removal) - Goal: Aggressive cleaning, high productivity - Constraint: Reusable media preferred for cost; heavy-duty application - Recommendation: _ - Justification: - Effectiveness: __ - Recycling potential: ___ - Cost over time: _______

Scenario 5: Educational/maker workshop (diverse beginners, priority on safety) - Goal: Introduce blasting technique; ensure user safety - Constraint: Cannot expose learners to high silica risk - Recommendation: _ - Justification: - Health/safety: __ - Learning environment fit: ___ - Trade-offs: _______

Step 4: Group Discussion & Synthesis (5 minutes)

  1. Each pair/group presents their hazard profile and application recommendations (1 minute per group)

  2. Class discussion:

  3. Why is silica particularly hazardous?
  4. What trade-offs must be made when choosing non-silica media?
  5. Why would a maker or small business choose a more expensive, less aggressive medium?
  6. How do you balance performance, cost, and safety?

Discussion Points

  1. "If crystalline silica is so dangerous, why is it still used?" — Explore economic/performance reasons; note the shift toward alternatives in progressive shops

  2. "What is the relationship between particle size and hazard?" — Introduce the concept of respirable dust (< 10 microns reaches the alveoli; larger particles are filtered by upper respiratory tract)

  3. "How would you justify the cost of a safer (non-silica) medium to a skeptical shop owner?" — Discuss liability, worker comp claims, reputation, and long-term ROI

  4. "Can someone be exposed to silica hazard without working directly with silica?" — Yes: secondary exposure (cleaning equipment, handling waste, or in the same workspace without proper controls)

Expected Outcomes

Learners will demonstrate: - Understanding of hazard profiles for five common blasting media - Ability to select appropriate media based on application requirements - Recognition of the occupational health implications of media choice - Appreciation for the trade-offs between performance, cost, and safety

Physical Outcomes: - Completed Media Observation Sheet - Completed Hazard Profile Table for assigned medium - Recommendations and justifications for five scenarios - Notes from group discussion

Knowledge Outcomes: - Understand why silica is uniquely hazardous (crystalline structure, respirable size, cumulative exposure, permanent lung damage) - Know at least three non-silica alternatives and their key properties - Appreciate the risk-benefit analysis required in media selection

Grading Rubric

Criterion 4 (Excellent) 3 (Good) 2 (Fair) 1 (Needs Improvement)
Media Observation Thorough, accurate visual assessment; good detail on hazard labels Mostly complete; minor details missed Adequate but superficial Incomplete or inaccurate
Hazard Research Deep understanding of health/environmental impact; comprehensive data Good understanding with minor gaps Basic understanding; missing some details Incomplete or incorrect
Application Recommendations Excellent media selection with clear, multi-factor justification Good selection with reasonable justification Adequate selection with partial reasoning Poor selection or weak justification
Discussion Participation Active engagement; insightful questions; builds on others' ideas Good participation; asks clarifying questions Listens but participates minimally Does not participate