Exposure to airborne dust, silica, asbestos, and chemical vapors can lead to a variety of diseases and even death. Respirators, when properly fitted and used, reduce the inhalation of airborne contaminants, including engineered nanomaterials. When engineering controls, administrative controls, and good work practices have been used to reduce the extent of the hazards on a jobsite, respirators can provide additional reduction of risk. This solution focuses on NIOSH-approved air-purifying respirators with an assigned protection factor (APF) of 10, the lowest level of respiratory protection, which includes elastomeric half mask and filtering facepiece respirators.

Engineering, administrative, and work practice controls are required by OSHA to be implemented to mitigate airborne hazards, with proper use of respirators being the last layer of protection when additional controls are necessary. Respirators are required by OSHA to be used as part of a complete and effective respiratory protection program implemented by the employer.

• Engineering controls, work practices, and administrative controls seek to reduce worker exposure to airborne contaminants. Engineering controls remove dust through local exhaust ventilation, tool-mounted vacuums, or wet work. Work practices rely on training, SOP’s, proper clothing, and equipment maintenance to reduce worker exposure to contaminants. Administrative controls minimize worker exposure through scheduling and work assignment rotations. These are discussed in more detail in OSHA’s Technical Manual.
• Respirators are used as an additional layer of protection to reduce worker exposure below the OSHA Permissible Exposure Limit (PEL) for the hazard. The APF tells you up to what level above the PEL a properly fitted respirator will protect a worker. For example, the PEL for asbestos is 0.1 fibers/cc, so a respirator with an APF of 10 will provide protection in an environment with exposure up to 1 fiber/cc. Note that for exposures such as asbestos or silica, which may cause cancer or other life-threatening diseases, measuring exposure levels at or near the PEL may be technically challenging and a protection factor of 10 may not be sufficient.
• Engineered nanomaterials are very small size (from 1 to 100 nanometers or so, roughly 100,000 times thinner than a human hair). Despite their very small size, NIOSH has demonstrated that engineered nanoparticles are efficiently captured by the filtering material used in respirators to capture airborne particulates. Consequently, respirators that are used to protect workers from asbestos and silica will also protect workers from airborne exposure to engineered nanoparticles.
• There are no OSHA PELs for any engineered nanomaterial. However, NIOSH has issued a Recommended Exposure Limit (REL) for carbon nanotubes of 1 µg/m3 elemental carbon as a respirable mass 8-hour time-weighted average (TWA) concentration for up to a 40-hour week (NIOSH, 2013). NIOSH also has an REL for ultrafine titanium dioxide of 0.3 mg/m3 as a time-weighted average (TWA) concentration for up to 10 hours/day during a 40-hour week (NIOSH, 2011).
• Respirators can also be used as an additional layer of protection to reduce worker exposure below the NIOSH REL for engineered nanomaterials. The APF tells you up to what level above the REL a properly fitted respirator will protect a worker. For example, with an REL for ultrafine titanium dioxide of 0.3 mg/m3, a respirator with an APF of 10 will provide protection in an environment with exposure up to 3.0 mg/m3.
• Respirators must be selected based upon the type and extent of hazard present in the work place. A qualified person should assess the worksite risks and follow the NIOSH respirator and filter selection logic. OSHA provides an online tool for respirator and filter or cartridge selection that follows the same logic. Respirators, cartridges, and filters must be certified by NIOSH and a searchable equipment list is available.
• A negative pressure APR works by creating a seal around the face of the worker. This seal prevents ambient air, which may be contaminated, from entering the worker’s breathing zone. Inhalation causes the pressure inside the mask to be lower than the ambient air pressure, pulling air through the filters, chemical adsorbing cartridges, or filter-cartridge combinations and into the workers lungs. When the worker exhales, air leaves through an exhalation valve that closes once pressure is equalized.
• Negative pressure respirators cannot be used in oxygen-deficient environments or with exposure to gases like carbon monoxide.
• Respirators offer protection against hazards only when partnered with the appropriate filters or cartridges. A HEPA filter will provide excellent protection against airborne particles like silica and construction dust, including nanometer-sized particles like engineered nanoparticles, but will do nothing for chlorine vapors. Filters and cartridges are hazard-specific, color-coded, and come in combinations to provide protection against multiple threats. Filters and cartridges are brand and style specific and cannot be swapped between non-identical respirators. Filters and cartridges must be changed on a regular basis as determined by the employer’s respirator change schedule.
• Particulate filters are rated by NIOSH based on how well they remove particles from the air. A filter with a rating of 95% filtration efficiency removes 95% of particles at 0.3 µm (300 nm) and research has shown that they are effective with even smaller particles, including engineered nanoparticles. This is discussed further in the Risks Addressed section below.

Particulate filters are also rated based on their resistance to oil, which is important because some oil can reduce the effectiveness of the filter. Construction work does not generate as much oil mist as factory operations, in most cases. The table below shows the types of filters available. A filter cartridge or filtering facepiece must have the proper designation printed on them to show their NIOSH approval. For example, an oil-resistant HEPA filter cartridge will indicate R100 on the label.

• Medical clearance is necessary when employees are required to wear a respirator for their job. This is discussed in more detail in the respiratory protection program solution.
• OSHA also requires fit testing prior to respirator use. While a medical clearance can cover multiple respirator types, fit tests are respirator specific and must be conducted for every brand, size, and style to be worn. Fit testing must be repeated at least once per year, after any face or dental surgery, and if the worker experiences a significant change in weight. Fit testing may be qualitative or quantitative.
• During qualitative fit testing the employee performs a set of tasks while exposed to an aerosol or vapor (video version). If the user detects the test agent then the test fails and the respirator cannot be used.
• Quantitative fit testing involves the use of a computerized system to determine fit factors during a variety of exercises. The most common quantitative fit testing method uses an instrument that compares the concentration of airborne particles inside and outside the facepiece to determine if the fit is adequate. Contaminants are more likely to get inside the facepiece from a poor fit than through the filter media. In the highly dusty environment of a construction site, this is significant. While the qualitative fit test ends in a pass/fail designation, the quantitative fit test provides an overall fit factor. These fit factors must be higher than the APFs for the respirators. OSHA requires a minimum fit factor of 100 to wear a half-mask respirator and 500 to wear a full-facepiece respirator. OSHA requirements for fit testing are available online.
• There are trade-offs between using disposable respirators, which are more comfortable and elastomeric, which are easier to fit reliably but need to be cleaned and stored between use.
• Employees must also perform a respirator seal check every time they wear their respirator. There are video examples of seal checks for a half face elastomeric APR and a filtering facepiece. Seal checks verify that the respirator is adequately sealed to the face.
• Respirators should be cleaned and inspected daily to ensure proper fit and function, with attention paid to checking particulate filters for breaks.

Use of air-purifying respirators has been found to impede physical effort, especially fine motor skills, and can impair cognitive functions.  Prolonged respirator use may be uncomfortable, reduce communication, and contribute to heat stress.  Claustrophobia may prevent some workers from using respirators.

People often confuse surgical masks with filtering facepiece respirators. Surgical masks do not provide adequate protection against airborne particles and are not NIOSH certified. The OSHA respiratory protection standard, 1910.134, only permits employers to use NIOSH certified respirators and prohibits the use of surgical masks to be used to protect workers from exposure to airborne inhalation hazards. NIOSH published a video and a blog entry to explain the differences between respirators and surgical masks. Additionally, many filtering facepiece respirators are not worn properly. Wearing the wrong size or failing to ensure that you have a proper face seal will significantly reduce the effectiveness. 

Engineered nanoparticles are very small, in the range of 1 to 100 nanometers. Both N95 and N100 or P100 filters perform as expected: penetrations of nanoparticles through the filter are below 5% for N95 and below 0.03% for N100 or P100 filters (Rengasamy et al, 2009). However, N95 filters do not perform as well against nanoparticles as, P100s due to the difference in filtering media. N95s use an electrostatic charge to trap particles which is more effective in capturing particles larger than nanoparticles, while N100s and P100s create a physical barrier that is more effective in capturing small particles in the nanoparticle size range (Balazy et al., 2006, Rengasamy and Eimer, 2012, Rengasamy et al, 2013).

Leakage around the seal of the respirator facepiece and the wearer’s face can also contribute to workers inhaling particles that leak into the wearer’s breathing zone. Using human test subjects, NIOSH researchers compared faceseal leakage performance of N95 filtering facepiece respirators against exposure to nanoparticles and to a full range of particle sizes and reported that faceseal leakage was not greater for nanoparticles compared to the full range of size particles (Zhuang et al, 2013).

 APF 10 is the lowest level of respiratory protection, and higher levels of exposure to hazards such as silica or asbestos or to oxygen deficient atmospheres will require other types of protection.

Other safety equipment needs, such as eye protection or hearing protection, should be considered when selecting a respirator.

Marc Scimonelli and Michael R. Cooper - Aria Environmental, Inc.
Bill Kojola, Bruce Lippy, CIH and Rosemary Sokas, MD, MOH - CPWR – The Center for Construction Research and Training