IH Particuate discussion 2/23/2026
Particle Size and Suspension
Definition of Particle Size
Particles wider than 100 microns often drop quickly and do not remain airborne.
Example: Wood dust blown from a table with compressed air; some stays airborne temporarily but most drops to the ground.
Importance of 100 Microns Cut-off
Particles larger than 100 microns tend to settle out and are not classified as airborne particles.
Range of Particulate Sizes
Size spectrum ranges from 1 nanometer to 1000 microns.
Examples of specific particles:
1000 microns: Rain droplets, beach sand.
100 nanometers ( e.g. Zika virus at 45 nanometers)
0.1 to 0.5 microns (e.g. Coronaviruses vary in size).
Particulates include: Plant spores, human hair, bacteria, tobacco smoke, coal dust.
Classification of Particulates
Categories of Particulates
Gases and vapors: less than 1 nanometer.
Mists and vapors produced in processes such as painting or plating.
Paint mist: mixture of solids and liquids when coating.
Example of a Mist
Chrome plating dip tank: includes agitation and heat that produces mist.
Welding Fumes
Defined as a classic example of fumes with recognized carcinogenic properties (Classified by IARC).
Terms to know:
Welding plume: Visible fume created during welding or cutting processes.
Types of Particulates and Their Environmental Effects
Differences Between Mist and Fog
Mist does not linger like fog does; fog represents finer particles.
Routes of Entry for Chemicals
Primary routes: Inhalation, absorption, and ingestion.
Hexavalent chromium noted as a dermal sensitizer.
Environmental and Health Regulations
OSHA PNOR: Particles Not Otherwise Regulated, specified limits for total (
) and respirable particles ().ACGIH terms: PNOS (Particles Not Otherwise Specified) with inhalable (10 mg/m³) and respirable versions (3 mg/m³).
Measurement and Sampling Techniques
Determining Exposure
Used for particulates lacking specific exposure standards.
Examples: Drywall dust or wood dust that doesn't have specific limits.
Understanding Particulate Size
Exposure limits defined under specific sampling methods:
Total, inhalable, thoracic, and respirable definitions based on size in microns.
Total: <100 ext{ microns}.
Inhalable: <10 ext{ microns}.
Thoracic: <4 ext{ microns}.
Respirable: Particles that penetrate the respiratory system.
Sampling Technology
Old standard cassette often samples inaccurately for particles larger than 30 microns, leading to misrepresentation of exposure data.
Newer technology (parallel particle impactor) captures particles more accurately based on size and flow.
Significant Health Considerations
Pneumoconiosis
General term for dust accumulation in lungs which can be reversible, stable, or progressive based on exposure ceasing or continuing.
Particle Deposition Mechanisms
Sedimentation: Heavy particles fall out of suspension due to gravity.
Inertial impaction: Particles collide with surfaces due to their velocity.
Diffusion or Brownian motion: Light particles exhibit random movement affected by currents.
Interception: Particles get caught in small spaces or gaps.
Electrostatic: Charged particles attracted to opposite charges.
Centrifugal action: Liabilities in cyclone samplers to separate heavier particles from lighter ones.
Thermal movement (phoretic): Gas or vapor movement based on temperature gradients.
Sampling Techniques for Airborne Particulates
Personal Breathing Zone (PBZ): Sampling typically done within a 9-inch radius around the mouth and nose of a worker.
Real-Time vs Integrated Sampling
Real-time allows for immediate exposure assessment but is limited in detail (does not specify particle type).
Integrated sampling provides average exposure data over time but requires laboratory analysis for identification.
Surface Sampling
Wipe samples used to assess surface contamination potential in operations, such as areas where respiratory sensitizers are expected.
Specific Case Studies and Procedures
Sodium Bisulfite Exposure Incident
Exposure levels verified through air sampling in a wastewater treatment context; sensitivity issues explored.
OELs established at .
Surface Sampling Procedure
Surfaces sampled using wipes, ensuring that cross-contamination is avoided.
Results interpreted based on specific surface limits where contamination might indicate violations of safety standards.
Current Sampling Practices and Technology
Highlighting the importance of using the latest sampling technology to ensure accurate assessments of both particulate and gaseous exposures in occupational settings.