by using electret filter material (usually, electrospun plastic fibers) to attract or repel particles with an electrostatic charge, so that they are more likely to collide with the filter surface

CEN/TC 79 - Atemschutzgeräte (2005). "Protection Factors [Anhang C. Schutzfactoren. C.2 Gebrauch von Schutzfaktoren]". DIN EN 529:2006-01 Selection, use and maintenance of respiratory protective devices [Atemschutzgeräte - Empfehlungen für Auswahl, Einsatz, Pflege und Instandhaltung - Leitfaden] (in German). Leitfaden: Gremium NA 027-02-04 AA “Atemgeräte für Arbeit und Rettung”. pp.35–36. {{ cite book}}: CS1 maint: numeric names: authors list ( link) Japanese Standards Association (2006). "Appendix 1. RPD selection". 呼吸用保護具の選択，使用及び保守管理方法[ JIS T 8150: 2006. Guidance for selection, use and maintenance of respiratory protective devices] (in Japanese). Tokyo: JSA. p.14 . Retrieved 3 June 2018. The electrostatic mechanism of attachment is weakened by rising speed. In addition to the mechanisms [ 66] (diffusion, interception, and inertial impaction), the charged filters displaying the electrostatic attachment are known as electrets filters in literature [ 63, 64, 67]. The majority of filters authorized by NIOSH (such as N95 and P100) are defined as the electrets filters [ 6].If the concentration of a harmful substance is less than the IDLH, the coefficient of air pollution for the harmful substance (Hazard Factor) is determined, which is equal to the ratio of this concentration to the PEL (TLV, OEL) for the harmful substance. The APF of the selected respirator type must equal or exceed the Hazard Factor. [17] [46] A few other jurisdictions use standards similar to the NIOSH scheme to classify mechanical filter respirators. They include: In a 1984 study by Myers et al., the WPF measurements for Powered Air Purifying Respirators (PAPRs) with helmets (that is not tight-fitted to the face) showed that the ingress of harmful substances in the inhaled air can be very high [23] (PF = 28 and 42 for two models). This came as a surprise, since earlier studies in the laboratory showed that the flow of clean filtered air from the inside to the outside of the helmet prevents ingress of harmful substances under the helmet (PF > 1000). Additional studies, [24] from 1986 and 1981, agreed with the result from the Myers et al. 1986 study: the minimum values of the workplace protection factors of two models of respirators were 31 and 23; and leakage of unfiltered air attained 16% in some cases in wind tunnel at 2m/s air velocity [25]

The minimum anticipated protection provided by a properly functioning respirator or class of respirators to a given percentage of properly fitted and trained users.Hyatt, E. C., J. A. Pritchard & C.P. Richards (1972). "Respirator Efficiency Measurement Using Quantitative DOP Man Tests". American Industrial Hygiene Association Journal. 33 (10): 635–643. doi: 10.1080/0002889728506721. ISSN 0002-8894. PMID 4512979. {{ cite journal}}: CS1 maint: multiple names: authors list ( link) National Personal Protective Equipment Standardization Technical Committee, 3M China Ltd. (2002). 4. 呼吸防护用品的选择[4. RPD selection]. In Yao, Hong (姚红); She, Qiyuan (佘启元); Ding, Songtao (丁松涛); Li, Xiaoyin (李小银); Liu, Jiangge (刘江歌); Nai, Fang (奈芳); Li, Qinhua (黎钦华) (eds.). 呼吸防护用品的选择、使用与维护[ GB/T 18664-2002 Selection, use and maintenance of respiratory protective equipment] (in Chinese). p.6. {{ cite book}}: CS1 maint: numeric names: authors list ( link) Canadian Standards Association (2011). CAN/CSA-Z94.4-11 Selection, use, and care of respirators (4ed.). Mississauga (Ontario, Canada). {{ cite book}}: CS1 maint: location missing publisher ( link) ISO/TS 16975-1 Respiratory protective devices. Selection, use and maintenance. Part 1: Establishing and implementing a respiratory protective device programme