Workplace Health Without Borders - UK CONTROL OF EXPOSURE
Controlling Exposure • Output from the risk assessment • Selection of control approach based upon: – The control hierarchy – Cost / benefit – Usability • More than one control option might be required
A Simple Exposure Model source transmission path Receiver
The Control Hierarchy • • • Elimination Substitution Engineering controls Management controls Personal protective equipment
Elimination • Unfortunately there are very few situations where RCS can be completely removed from the work environment. • Where crystalline silica is used in a process we should ask if is an essential part of the process. • If it is not it may be possible to remove it completely or to substitute it with something less hazardous.
Tragedy of the Jeans • Manufacturers in Turkey used sandblasting to give jeans a weathered look • Sand was used to blast the jeans without any controls • This resulted in the deaths of more than 50 workers and lung disease in many others. Source - WHWB
Substitution • Sandblasting with sand has been used extensively to change the surface properties of a variety of materials • Substitute other material for the sand which has traditionally been used in sandblasting for example • Some substitutes are walnut shells, metal beads, steel shot • Chemicals can be used to remove surface coatings • High pressure water can used in some application such as bridge deck refurbishing. Source - WHWB
Wet Methods • One very effective means of reducing emissions of RCS containing dust into the air is to use a wet method. • This method entails adding water to the process to capture the dust at source.
Wet Methods Dry sawing concrete Wet sawing concrete water is added at saw blade Notice puddle at feet of wet saw operator. It contains the same amount of dust as seen in picture of dry saw operator. What happens to the dust when puddle dries? Pictures from OSHA Source - WHWB
Engineering Controls • Engineering controls work by: – Enclosing the process to prevent the dust from escaping into the environment – Using local exhaust ventilation to draw away the dust before it disperses into the environment – Using fresh air to dilute the dust concentration in the air – Isolating the worker from the contaminated air.
Isolate the Process • Using covers on conveyor belts • Using a glove box for sandblasting Source - WHWB
Enclose Dumping Process • Ventilation • Wetting (1% moisture by weight) – Activate with photocell or mechanical switch Diagram from MSHA Source - WHWB
Isolate the Worker • Positive pressure inside cab • HEPA filters on cab intake • HEPA recirculation filter • Minimize dust sources in the cab • Keep doors and windows closed Source - WHWB Image from MSHA
Keep Doors and Windows Closed Respirable dust in cab with doors closed: 0. 09 mg/m 3 Respirable dust in cab when door opened briefly: 0. 81 mg/m 3 Source - WHWB
Minimize Dust Sources in Cab • Good housekeeping • Move air vents that blow across cab floor Dust levels Before floor vent turned on: 0. 03 mg/m 3 After floor vent turned on: 0. 26 mg/m 3 Image from MSHA Source - WHWB
Local Exhaust Ventilation • Local exhaust ventilation (LEV) systems only work if the are designed and used correctly. • A good LEV system will control the dust at source and prevent it escaping into the environment. • LEV systems can be expensive to install and maintain and require a reliable energy source to run.
Local Exhaust Ventilation Filter Hood Ducting Fan Induced airflow source Contaminant emission Airflow through LEV system
WHWB RCS Control Project No Ventilation, Feb. 2015 Respirable Dust: 1. 7 mg/m 3 Quartz = 1. 2 mg/m 3 Agate Polishing Vertical Grinder - Dry 18
WHWB RCS Control Project • With local exhaust, October 2015 • Respirable dust 0. 64 mg/m 3 • Respirable silica 0. 10 mg/m 3 19
Reduce dust at the Source • Wetting reduces dust but the wet dust must be collected • Dust on unpaved roads and surfaces gets continually stirred up and exposes everyone to respirable crystalline silica • Dust collected in enclosures or by local ventilation must be disposed of properly • Proper disposal means removing the dust permanently, for example, burying it or reincorporating it into soil. Source - WHWB
Remember …. Visual dust emissions indicates that a control is needed or an existing control needs maintenance. Respirable dust that has been wetted or removed through ventilation must be collected and disposed of properly
Personal Protective Equipment • Personal protective equipment (PPE) only protects the individual. • Only provides protection if the correct equipment is chosen and used correctly. • Should be only used when other control options are not practicable or do not provide adequate protection.
Personal Protective Equipment • PPE includes: – Gloves – Overalls / work clothes – Protective glasses and visors – Respiratory protective equipment (RPE)
Respiratory Protective Equipment • RPE works by filtering the contaminated air before it is breathed by the worker. • It will only provide adequate protection if: – It is the correct type of PPE for RCS at the concentrations the worker is exposed to. – It is correctly worn – It is maintained and replaced when required