Airborne dusts, fumes and mists all pose an inhalation hazard to humans, depending on the type and amount of the airborne material. Acute doses (large amounts in a relatively short time period) can be very harmful, but even smaller doses over a long time period can build-up in the body and cause latent health issues. Particulate matter less than 10 µm in size is considered a respirable fraction and cannot be filtered as it passes through the trachea; therefore, it enters the lungs and the bloodstream. The unaided human eye cannot see particles smaller than 50 µm, so it isn’t always obvious when respiratory protection is needed. This brief article discusses respiratory protection for the coatings industry.
Potential Respirable Health Hazards in the Coatings Industry
Potential respirable health hazards in the coatings industry can be found in the, surface preparation, coating removal and coatings system application processes. A coating system generally consists of a pigment and a vehicle. The pigment is the particulate solid used to impart protective or decorative qualities of the system. Many industrial coatings used (or still use) metals such as lead, chromium, cadmium, cobalt, and zinc derivatives as pigments. The vehicle is the liquid base of the coating that carries the pigment. Solvents such as methyl ethyl ketone, toluene, and methyl alcohol are present in the vehicle. Respirable exposure to metals and solvents has the potential to cause damage to the nervous system, respiratory, reproductive, renal, blood-forming, urinary, and dermal systems.
Other potential respirable health hazards include isocyanates, liquid epoxy resins and curing agents, and crystalline silica. The crosslinking polymers in urethane and urethane-derived coatings such as polyurethanes are isocyanates. Airborne exposure to isocyanates may result in symptoms such as chest pains, vomiting, hypersensitivity pneumonitis, and asthmatic reactions. Respirable exposure to reactive diluents – such as glycidyl ethers found in liquid epoxy resins and aliphatic and aromatic polyamides in curing agents are irritants and sensitizers to the respiratory tract. Crystalline silica may be used as a pigment extender in a coating system or may be present during coating removal operations on concrete or while using sand as an abrasive. Respirable crystalline silica exposure may result in the growth of fibrous tissues in the lung, possibly leading to a debilitating lung disease known as silicosis.
Evaluating Respiratory Hazards
The evaluation of potential health hazards is the first step towards determining the level or degree of respiratory protection required. The three components to be evaluated include the coating system, job site factors, and the potential exposure levels. Review of the Safety Data Sheet (SDS) for the coating components, accelerators, thinners, and other products to be used in the coating application is a critical first step. The SDS will reveal the chemicals that present a potential respiratory hazard, the permissible exposure limits, and hazard controls such as engineering controls and personal protective equipment to be employed. Job site factors may have a major impact on airborne concentrations of respirable hazards, and may include ventilation, and application in a confined space. Once the respirable hazards are defined, the next step is to evaluate the airborne concentrations that are impacted by jobsite conditions. This can be accomplished in three ways, historical data, objective data, and air monitoring or sampling. This step will determine if permissible exposure limits will be exceeded, and will drive decisions regarding implementation of engineering controls, work practices (administrative controls) and personal protective equipment to reduce the hazard to the extent feasible.
Controlling Respiratory Hazards
Once the respirable hazards are identified the next step is to select and implement hazard controls. OSHA identifies a hierarchy of three lines of defense, including implementation of (1) engineering controls (e.g., ventilation), (2) administrative controls (e.g., worker rotation), and (3) personal protective equipment (e.g., respirators). Once engineering and administrative controls are deployed, if a respirable hazard remains the last line of defense is the reliance on respiratory protection.
Types and Uses of Respiratory Protection in the Coatings Industry
Respiratory protection requires a written respiratory protection program that includes:
- Program administration
- Standard operating procedures
- Exposure assessment
- Medical evaluation for respirator users
- Selection of a respirator
- Fit testing
- Positive and negative pressure fit checks (for air purifying respirators)
- Cleaning, maintenance and storage of the respirator
Though each element of the program is important we will focus on the different types of respirators available. Selection of the correct (proper) respirator is based on the type (or class) of respirator, type of cartridge, and the assigned protection factor, all of which must be considered.
Respirators are grouped in the following four classes:
- Air-Purifying Respirator (APR)
- Powered Air-Purifying Respirator (PAPR)
- Supplied-Air Respirator (SAR)
- Self-Contained Breathing Apparatus (SCBA)
Air-purifying respirators are categorized into three separate types, including particulate, gas and vapor, and combination air purifying respirators. Air-purifying respirators are not to be used in an oxygen enriched or deficient atmospheres, nor in atmospheres Immediately Dangerous to Life or Health (IDLH).
Particulate respirators capture the particulates in the air, such as dusts, mists, and fumes. They will not protect the user from gases or vapors. Particulate respirators have a N, R, or P designation followed by one of three numeric values. The N, R, or P designation refers to the oil resistance of the filter ranging from N = not resistant, R = somewhat resistant, and P = strongly resistant. Exposure to some oils as example during power hand tool use may reduce the effectiveness of the filter. The numerical values identify the filtration level of the respirator. The levels are associated with a percent effectiveness, and are identified as 95, 99, or 100 (99.97%). Therefore, a P100 air purifying respirator is strongly resistant to oils, and has a 99.97% level of filtration (efficiency). This type of respirator is commonly donned to protect the wearer from exposures to heavy metals such as airborne particulates of lead.
Gas and vapor air-purifying respirators use replaceable chemical cartridges or canisters to remove specific gases or vapor contaminants, they are color-coded, and may require more than one cartridge to protect against multiple respiratory hazards.
For example, an employee working in the coatings industry exposed to organic vapor respiratory hazards (e.g., solvent vapors) would select a respirator color-coded as black. Combination (“stacked”) cartridges are normally used in atmospheres that contain hazards of both particulates and gases and vapors. A worker exposed to organic vapors and respirable particles would select a cartridge or canister color-coded black for organic vapors and magenta for P100 particulate protection. Chemical cartridges or canisters provide protection only as long as the filter’s absorbing capacity is not depleted, and do not protect against airborne particulates.
Atmosphere-Supplying respirators are used in environments where air purifying respirators cannot give the wearer sufficient protection from atmospheric hazards. The types include, air-supplied (ASR) (line), Self-Contained Breathing Apparatus (SCBA), and combination ASR, SCBA. OSHA requires the use of Grade D breathing air as described in the American National Standards Institute/Compressed Gas Association Commodity Specification for Air.
Grade D air requirements:
- Oxygen content between 19.5% and 23.5%
- Maximum 5 milligrams per cubic meter (mg/m3) Hydrocarbon content
- Maximum 10 ppm Carbon monoxide content
- Maximum 1,000 ppm Carbon dioxide content
- No noticeable odors
Air-supplied (or line) respirators (ASR) are used when there are extended work periods required in atmospheres that contain a respiratory hazard, but are not immediately dangerous to life and health (IDLH). They use an airline hose to deliver clean, breathable air from an uncontaminated source (Grade D air) for long periods of time. ASR are advantageous due to their inherent lightweight relative to the weight of a SCBA. However, they limit the range of mobility and may fail due to hose damage. A common ASR used in the coatings industry during abrasive blast cleaning is the type CE respirators (i.e., blast helmets) certified by NIOSH.
Self-contained breathing apparatuses are commonly used when there is a short-time need to enter and escape from atmospheres that are or may be immediately dangerous to life and health (IDLH). They consist of a wearable, clean air supply pack, and do not restrict movement with a hose connection. Open-circuit types only provide air for 30 – 75 minutes, closed circuit types can provide air up to four hours. SCBA are typically used in the coatings industry for rescue purposes.
When working in an IDLH environment, or when work activities have the potential to create an IDLH environment a combination atmosphere-supplying respirator may be deployed. A combination ASR includes both a SAR and SCBA, and they provide the extended work periods of the SAR with an auxiliary self-contained air supply that can be used for escape if the primary supply fails. Auxiliary self-contained portion is generally small since it only needs to supply enough air for escape. Combination atmosphere-supplied respirators can be used for entry into confined spaces during coatings applications.
Assigned Protection Factors
The Occupational Safety and Health Administration (OSHA) issued assigned protection factors (APFs) and maximum use concentrations (MUCs) for each of the unique types of respiratory protection. Assigned Protection Factor (APF) is the workplace level of respiratory protection that a respirator or class of respirators is expected to provide to a worker. Maximum use concentration (MUC) is the maximum atmospheric concentration of a hazardous substance that an employee can be expected to be protected from, and is determined by the assigned protection factor of the respirator or class of respirators and the exposure limit of the hazardous substance.
The MUC is calculated by multiplying the APF for the respirator by the permissible exposure limit (PEL) of the contaminant.
For example, let’s assume that an employee performing abrasive blast cleaning operations to remove a lead based coating system has donned a SAR abrasive blast helmet with an APF of 1,000. OSHA established the PEL for inorganic lead at 50 micrograms per cubic meter of air over an 8-hour time weighted average. The MUC is calculated as 1,000 x 50, or 50,000 micrograms per cubic meter airborne lead concentration. Whenever the exposures approach the MUC, the employer must select the next higher class of respirator for the employee, and employers must not apply MUCs to conditions that are IDLH.