Newsletter RSS Feeds 

### What's New| Offices

<< Back to Dust Control Handbook for Minerals Processing 

# Chapter 1: Dust and Its Control For problems with accessibility in using figures and illustrations in this document, please contact the Directorate of Technical Support and Emergency Management at (202) 693-2300. 

## What Is Dust? Dust consists of tiny solid particles carried by air currents. These articles are formed by a disintegration or fracture proces s, such as grinding, crushing, or impact. The Mine Safety and Health Administ ration (MSHA) defines dust as finely divided solids that may become airborne from the origin al state without an y chemical or physical ch ange other than fracture. A wide range of particle size is produced during a dust generating process. Particles that are too large to remain airborne settle while others remain in the air indefinitely. Dust is generally measured in micrometers (commonly known as mi crons). Some common objects and their size in microns are listed below. μm Red blood corpuscles 8 Human hair 50-75 Cotton fiber 15-30 

## How Is Dust Generated? Dust is generated by a wide range of manuf acturing, domestic, and industrial activiti es. Construction, agriculture, and mining are among the industri es that contribute most to atmospheric dust levels. In minerals processing operations, dust is emitted-
◾ When ore is broken by impact, abrasion, crushing, grinding, etc. ◾ Through release of previously generated dust during op erations such as loading, dumping, and transferring ◾ Through recirculation of previously generated dust by wind or by the movement of workers and machinery The amount of dust emitted by these activities depends on the ph ysical characteristics of the material and the way in which thematerial is handled.



## Types Of Dust Fibrogenic dust, such as free crystalline silica (FCS) or asbestos, is biologically toxic and, if retained in the lungs, can fo rm scar tissue and impair the lungs' ability to function properly. Nuisance dust, or inert dust, can be defined as dust that contains less than 1% quar tz. Because of its low content of silicates , nuisance dust has a long history of having little adve rse effect on the lungs. Any reaction that may occur from nuisance dust is potenti ally reversible. However, excessive concentrations of nuisance dust in the workplace may reduce visibility (e.g., iron oxide), may c ause unpleasant deposits in eyes, cars, and nasal passages (e.g., portla nd cement dust), and may cause injury to the skin or mucous membranes by chemical or mechanical action. From an occupational health point of view, dust is classified by size into three primary categories:
◾ Respirable Dust ◾ Inhalable Dust ◾ Total Dust A to Z Index | Newsroom | Contact Us| FAQs| About OSHA 

### OSHA

Home Workers Regulations Enforcement Data & Statistics Training Publications Newsroom Small Business Anti-Retaliation 

# Page 1 of 4 Silica, Crytalline - Dust Control Handbook, Chapter 1: Dust and Its Contro l

8 / 13 /201 5 https://www.osha.gov/dsg/topics/sil icacrystalline/dust/chapter_1.htm lRespirable Dust Respirable dust refers to those dust particles that are small en ough to penetrate the nose and upper respiratory system and dee p into the lungs. Particles that penetrate deep into the respiratory system are generally beyond the body's natural clearance mechanisms of cilia and mucous and are more likely to be retained. MSHA defines respirable dust as the fracti on of airborne dust that passes a size-selecting device, having the following characteristics: Aerodynamic diameter Percent μm passing (unit density spheres) selector 2.0 90 2.5 75 3.5 50 5.0 25 10.0 0 Inhalable Dust The EPA describes inhalable dust as that size fraction of dust which enters the body, but is tr apped in the nose, throat, and u pper respiratory tract. The median aerodynamic diameter of th is dust is about 10 μm. Total Dust Total dust includes all airborne particles, regardless of their size or composition. 

## Why Is Dust Control Necessary? Although unavoidable in many minerals proc essing operations, the escape of dust part icles into the workplace atmosphere is unde sirable. Excessive dust emissions can cause both health and industrial problems:
◾ Health hazards

- Occupational respiratory diseases - Irritation to eyes, ears, nose and throat - Irritation to skin ◾ Risk of dust explosions and fire ◾ Damage to equipment ◾ Impaired visibility ◾ Unpleasant odors ◾ Problems in community relations Of greatest concern is the health hazard to workers who are excessively exposed to harmful dusts. In order to evaluate the seve rity of health hazard in a workplace, the American Conference of Governmental Industrial Hygienists (ACGIH) has adopted a number of standards, commonly known as thre shold limit values (TLVs). These values are used as guides in the evaluation of health hazards. TLVs are time-weighted concentrations to which nearly all worker s may be exposed 8 hours per day over extended periods of time without adverse effects. MSHA uses these TLVs for health hazard evaluation and enforcement. 

## Health Hazard Factors Not all dusts product the same degree of health haza rd; their harmfulness depends on the following factors:
◾ Dust composition

- Chemical - Mineralogical ◾ Dust concentration

- On a weight basis: milligrams of dust per cubic meter of air (mg/m3) - On a quantity basis: million particles per cubic foot of air (mppcf) ◾ Particle size and shape

- The particulate size distribution within the respirable range - Fiberous or spherical ◾ Exposure time

Excessive or long-term exposure to harmful respirable dusts may result in a respiratory disease called pneumoconiosis. This dis ease is caused by the buildup of mineral or metallic dust particles in the lungs and the tissue reaction to their presence. Pneumoconiosis is a general name for a numbe r of dust-related lung diseases. Some types of pneumoconiosis are: 

# Page 2 of 4 Silica, Crytalline - Dust Control Handbook, Chapter 1: Dust and Its Contro l

8 / 13 /201 5 https://www.osha.gov/dsg/topics/sil icacrystalline/dust/chapter_1.htm l◾ Silicosis- Silicosis is a form of pneumoconiosis caused by the dust of quartz and other silicates. The condition of the lungs is marked by nodular fibrosis (scarring of the lung tissue), resulting in shortness of breath. Silicosis is an irreversible disease; advanced stages are prog ressive even if the individual is removed from the exposure. ◾ Black Lung - Black lung is a form of pneumoconiosis in which respirable coal dust particles accumulate in the lungs and darken the tissue . This disease is

progressive. Although this disease is commonly known as black lung, its official name is coal worker's pneumoconiosis (CWP). ◾ Asbestosis - Asbestosis is a form of pneumoconiosis caused by asbestos fibers. This disease is also irreversible. 

## How Is Dust Controlled? Dust control is the science of reducing harmful dust emissions by applying sound engineering principles. Properly designed, mai ntained, and operated dust control systems can reduce dust emissions and, thus workers' exposure toharmful dusts. Dust control systems can also reduce equipment wear, maintenance, and downtime; increase visibility; and boost em ployee morale and productivity. Reducing employee exposure to dust can be accomplished by three major steps:
◾ Prevention ◾ Control Systems ◾ Dilution or Isolation Prevention The saying "prevention is better than cure" can certainly be appl ied to the control of dust. Alth ough total prevention of dust in the bulk material handling op eration is an impossible task, properly designed bulk material handling components can play an important role in reducing dust generation, emission, and dispersion. Control Systems After all the necessary preventive measures have been adopted, th e dust still remaining in the workplace can be controlled by o ne or more of the following techniques: dust collection systems, wet dust suppression system s, and airborne dust capt ure through wa ter sprays. Dust Collection Systems Dust collection systems are industrial ventilation principles to capture airborne dust from the source. The captured dust is th en transported to a dust collector, which cleans the dusty air.

Wet Dust Suppression Systems Wet dust suppression systems use liquids (usually water) to wet th e material so that it has a lo wer tendency to generate dust. Keeping the material damp immobilizes the dust, and very little material becomes airborne.

Airborne Dust Capture Through Water Sprays This technique suppresses airborne dust by spraying fine dropletsof water on the dust cloud. Th e water droplets and dust parti cles collide and form agglomerates. Once these agglomerates become too heavy to re main airborne, they settl e from the air stream. 

## Dilution-Isolation Dilution Ventilation This technique reduces the dust concentration in the area by di luting the contaminated air with uncontaminated fresh air. In ge neral, dilution ventilation is not as satisfactory for health ha zard control or dust collecting sy stems; however, it may be applied in circumstances where the operat ion or process prohibits other dust control measures. Isolation Isolation is another means to protect workers from exposure to ha rmful dust. In this technique, the worker is placed in an encl osed cab and supplied with fresh, clean, filtered air.

Freedom of Information Act| Privacy & Security Statement| Disclaimers| Important Web Site Notices| International | Contact Us 

# Page 3 of 4 Silica, Crytalline - Dust Control Handbook, Chapter 1: Dust and Its Contro l

8 / 13 /201 5 https://www.osha.gov/dsg/topics/sil icacrystalline/dust/chapter_1.htm lU.S. Department of Labor | Occupational Safety & Health Ad ministration | 200 Constitution Ave., NW, Washington, DC 2021 0 Telephone: 800-321-OSHA (6742) | TTY 

### www.OSHA.gov 

# Page 4 of 4 Silica, Crytalline - Dust Control Handbook, Chapter 1: Dust and Its Contro l

8 / 13 /201 5 https://www.osha.gov/dsg/topics/sil icacrystalline/dust/chapter_1.htm l