Safety & Health in the Stone Crushing Industry - Occupational ...

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We will discuss these solutions in the next chapters. You will find information on dust reduction
systems that use
(a) water sprayers or
(b) a ventilation system
A.3.1 Reducing Dust When Water is Available
Perry Gottesfeld, Occupational Knowledge International, San Francisco USA
Water spray dust control measures are effective at reducing respirable crystalline silica dust. Studies
have reported significant reductions with the use of wet methods to control silica dust in various
applications including stone crushing, construction, mining, and manufacturing industries.
Reductions in respirable dust in stone crusher mills can be accomplished through engineering controls
including process enclosures (or containment), dust collection (or local exhaust ventilation), and water
spray systems. Water spray suppression systems may be pressurized or rely on available water
pressure. Basic systems without pressurization can be effective at significantly reducing respirable
silica if an adequate number of well positioned spray nozzles are used.
Silica content is known to vary greatly from area to area and may help to determine the necessary
extent of controls. Quarry and mill owners can test samples of the rock to determine the silica content.
Water Spray System Design
The spray nozzle is selected to achieve the desired spray characteristics, velocity, spray pattern and
angle. Below is a general discussion of these factors:
Droplet and Orifice Size: Droplet size is the most important variable for proper dust control and is
determined by the orifice size and available pressure. The smallest droplets are generated with
pressurized systems.
Droplet Velocity: Normally, higher droplet velocities are desirable for dust suppression control.
Information on the droplet velocity, based on the available water pressure, can be obtained from the
nozzle manufacturer.
Spray Pattern: Nozzles are categorized by the spray patterns they produce. The following describes
the different spay nozzles used in dust control:
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Full-cone nozzles produce a round spray pattern and provide high velocity over a distance. These
nozzles provide optimal surface area coverage for non-pressurized spray systems
Hollow-cone nozzles produce a spray pattern in the form of circular ring. Droplet range is
normally smaller than the other types of nozzles
Flat-spray nozzles produce a rectangular or even spray pattern. They also produce relatively
large droplets that are delivered at high pressure
Air Atomizing nozzles require a pressurized system to produce very fine mist. They are very
effective in locations where airborne dust particles are extremely small and nozzles can be located
in close proximity to the dust source
Spray Angle: The spray angle determines the width of the cone-shaped spray pattern produced by the
nozzle. The appropriate spray angle needed to cover a specific surface area would depend on the
distance the nozzle is placed from the material.