Respiratory Protection with an Assigned Protection Factor (APF) of 10

Respirators with APF 10, when properly fitted and used, reduce the inhalation of airborne contaminants.


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.


Resistance to Oils

Minimum Efficiency

N (not oil resistant)

R (oil resistant)

P (oil proof)













  • 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.

Examples NIOSH-Approved Filtering Facepiece and Elastomeric Respirators

3M™ Aura™ N95 Particulate Respirator 9211+/37193(AAD)

(Photo courtesy of 3M)

  • Exhalation valve directs exhaled breath away from glasses
  • Design allows more room for eyewear
  • Ideal use: grinding, sanding, sweeping, bagging and other dusty operations

Northern Safety & Industrial 7210 N95 Disposable Respirator Mask

  • ASoft inner shell material and padded nosepiece deliver all-day comfort
  • 95% filter efficiency against solid and non-oil based particulates
  • Adjustable noseclip reduces fogging and offers a secure fit
  • Manufactured in an ISO 9002 Registered and ISO 14001 Certified facility
  • 20 per box

3M™ P100 Particulate Respirator (8293)

(Photo courtesy of 3M)

  • Exhalation valve directs exhaled breath away from glasses
  • Adjustable buckle straps
  • Foam faceseal
  • Ideal use: lead abatement and pharmaceutical manufacturing

3M™ Half Facepiece Respirator Assembly 6391/07003(AAD) with P100 Particulate Filters (2091)

(Photo courtesy of 3M)

  • Comes with 2 P100 filters
  • Additional filter cartridge types available
  • Ideal use: grinding, sanding, sweeping, bagging, vacuuming, mold cleanup

Risks Addressed:

Chronic silica inhalation has been linked to an increased risk for multiple types of cancer, COPD, and silicosis. Welding fumes are known to cause metal fume fever and are also associated with Parkinsonism. Increasingly, nano-enabled construction products are being used in construction that can also expose workers to inhaling engineered nanomaterials when the products are being disturbed, such as concrete roofing tiles that contain nano-size titanium dioxide. Inhalation of ultrafine titanium dioxide particles may increase the risk of workers developing lung cancer and other respiratory diseases (NIOSH, 2011). APRs, when properly used, can effectively reduce the inhalation of particles. APRs do not provide breathing air and must not be used in oxygen-deficient or immediately dangerous to life and health environments, which may include confined spaces.

In a construction setting, workers are most often exposed to nuisance, wood, and silica dusts. Exposure to these can cause pulmonary illnesses, and silica dust exposure can lead to silicosis and death. All construction dust acts as an irritant to nasal, throat, and lung tissues, resulting in reduced respiratory capacity. Chronic exposure leads to a heightened risk for respiratory infections, bronchitis, pneumonia, tuberculosis, COPD, and cancer. With the increasing use of nano-enabled construction materials, workers can also expect to have an increased likelihood of being exposed to engineered nanomaterials along with silica and other construction dust. While there is no evidence yet that engineered nanomaterials cause harm in humans, animal studies have demonstrated that some engineered nanomaterials, such as titanium dioxide and carbon nanotubes, can cause adverse effects on the lungs, including lung cancer (NIOSH, 2011; NIOSH, 2013).

Silicosis occurs when inhaled silica dust causes scarring of the lungs, causing difficulty breathing.  Silicosis is not restricted to people with chronic exposure. Short-term exposure to very high levels of silica dust can cause acute silicosis, which can be fatal within months.  Air filtering respirators with an APF of 10 are not sufficient for high dust exposures.  Unless air monitoring documents silica dust exposures consistently less than 10 times the Permissible Exposure Limit, higher forms of respiratory protection must be used.  APF 10 respirators should only be used in addition to effective dust suppression using wet methods or local exhaust ventilation. In construction products that contain both silica and an engineered nanomaterial like titanium dioxide, workers are most likely exposed to far more risk of harm to their health from exposure to silica than the health risk resulting from exposure to the engineered nanomaterial. That means that selection of the appropriate form of respiratory protection that effectively protects workers from the risk of silica will be sufficient to also protect workers from any health risks that may be associated with exposure to the engineered nanomaterial.

How Risks are Reduced:

A well-fitted APR forms a tight seal around the face ensuring that air must travel through the filter or cartridge before being inhaled. Filters remove solid contaminant particles. N95 filters are lighter material and trap particles using an electrostatic media to grab particles. N99 and N100 filters are a heavier material and physically block the passage of particles through the media. Cartridges for chemical vapors and gases work by trapping vapors onto an absorbent media. These media are specific to the gas or vapor and are limited by the attraction between chemical and media, as well as the available surface area for adsorption.

For workers exposed to engineered nanomaterials, NIOSH has concluded that N95 and P100 particulate filters provide the expected filtration efficiency according to their efficiency ratings (Rengasamy, et al 2009). However, both OSHA and NIOSH recommend that N100 or P100 filters be used when workers are exposed to high levels of airborne engineered nanomaterials (OSHA Fact Sheet FS-3634;  NIOSH blog post December 7, 2011). Surveys have shown that the most common respirators that are in use against engineered nanomaterials are P100 filters on elastomeric half mask or filtering facepiece respirators (Conti, et al 2008).

APRs work by filtering particles from the air or chemically purifying the air. APRs and filters are independently certified by the National Personal Protective Technology Laboratory (NPPTL) at NIOSH. These results have been verified independently in multiple peer reviewed journal articles, and the U.S. Army Research, Development, and Engineering Command. N95 and P100 filters are certified to remove 95% and 99.97%, respectively, of 0.3 µm diameter (300 nm) particles, the most difficult size to capture. The Army nanoparticle research has shown effectiveness at sizes down to 50 nm. This is significant for construction applications because it shows that proper use of respirators can significantly reduce exposure to airborne particles of any size on a job site. NIOSH has also confirmed that particulate filtering respirators are effective in capturing particles in the size range of engineered nanomaterials so that these respirators will work to reduce inhalation when exposed to airborne nanoparticles.

A simulated workplace protection factor study conducted by NIOSH has shown that elastomeric half mask and filtering facepiece respirators equipped with P100 filters provide a higher level of protection against exposures to nanoparticles than elastomeric half masks and filtering facepiece respirators with N95 filters (Vo et al 2015; Zhuang et al 2015). This finding supports the NIOSH and OSHA recommendation that N100 or P100 filters be used when workers are exposed to high levels of airborne engineered nanomaterials.

Effects on Productivity:

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.

Additional Considerations:

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



To obtain information, visit Aura™ N95 Particulate Respirator 9211+/37193(AAD) and Half Facepiece Respirator Assembly 6391/07003(AAD) and Particulate Respirator 8293 or contact 1-800-364-3577

Northern Safety & Industrial
To obtain information, visit 7210 N95 Disposable Respirator Masks or contact 1-800-571-4646

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