|Year : 2019 | Volume
| Issue : 3 | Page : 77-83
Evaluation of protection factor of respiratory protective equipment using indigenously developed protection factor test facility
G Ganesh, DS Patkulkar, MS Kulkarni
Health Physics Division, BARC, Mumbai, Maharashtra, India
|Date of Submission||17-Jul-2018|
|Date of Decision||23-Jul-2018|
|Date of Acceptance||13-Apr-2019|
|Date of Web Publication||06-Nov-2019|
Mr. G Ganesh
Health Physics Division, BARC, Mumbai - 400 085, Maharashtra
Source of Support: None, Conflict of Interest: None
Protection factor (PF) of a respirator is a number that describes the effectiveness of various classes of respirators in providing protection against exposure to airborne contaminants (including particulates, gases, vapors, and biological agents). The PF is derived from the ratio of the concentration of an airborne contaminant (e.g., hazardous substance) outside the respirator (Co) to the concentration inside the respirator (Ci) (i.e., Co/Ci). As the PF increases, there is an increase in the level of respiratory protection provided to employees by the respirator. PF Test Facility for the estimation of PF for various respiratory protective equipment was designed, fabricated, and installed at the Respiratory Protective Equipment Laboratory of Health Physics Division. The test facility consists of established air flow at a breathing rate through respirator darn on a human dummy and two identical tapings for iso-kinetic sampling from outside and inside the respirator. These tapings are coupled to two identical optical particle counters (OPCs) for the measurement of aerosol concentration simultaneously, and data acquired by the two OPCs are analyzed for estimating PF for different particle sizes using GRIM AEROSOL software. The results obtained from the studies carried out using this unique setup – air-purifying respirators such as half face mask, full face mask, and powered air-purifying respirators – were found offering a PF of 14, 112, and 1328, respectively, for selected range of 0.28–0.3-μm size standard sodium chloride (NaCl) aerosols. Standard NaCl aerosols used in experiments are polydispersed. However, the 0.3 μ size range (0.28–0.3) was selected as a benchmark for efficiency ratings and PF of respirators because it approximates the most difficult particle size for filters to capture and the least filtration efficiency is obtained in this range. This article brings out the details of design features of the setup and studies and results obtained for various types of respirators used in nuclear facilities.
Keywords: Aerosol, particle size, protection factor, respirator
|How to cite this article:|
Ganesh G, Patkulkar D S, Kulkarni M S. Evaluation of protection factor of respiratory protective equipment using indigenously developed protection factor test facility. Radiat Prot Environ 2019;42:77-83
|How to cite this URL:|
Ganesh G, Patkulkar D S, Kulkarni M S. Evaluation of protection factor of respiratory protective equipment using indigenously developed protection factor test facility. Radiat Prot Environ [serial online] 2019 [cited 2022 Nov 29];42:77-83. Available from: https://www.rpe.org.in/text.asp?2019/42/3/77/270445
| Introduction|| |
A respiratory protective device is considered adequately safe for the worker if it reduces the exposure to a hazardous substance to acceptable levels, for example, to comply with occupational exposure limit values. Each respirator has a protection factor (PF) assigned to it, which is the ratio of the airborne concentration of the substance outside the respirator (Co) to that inside the respirator (Ci). There are three types of PF as follows: assigned PF (APF), which reflects the workplace conditions, is the value to be used when selecting a particular type of respirator; nominal PF reflects the testing conditions carried out in a laboratory situation, and this level of protection is unlikely to be achieved in real use situations and does not give a good estimate of the effectiveness of the respirator; and workplace PF is the ratio between the breathing zone concentration of the contaminant outside the facepiece and the concentration inside the facepiece of the contaminant for a properly functioning respirator.
APF is an indicator representing the performance or effectiveness of a respirator in providing protection against exposure to airborne contaminants. It provides the workplace level of respiratory protection offered by a respirator or a class of respirators for workers in a continuing and effective respiratory protection program. APFs provide critical information for selecting appropriate type of respirators for employees exposed to various hazardous contaminants found in the workplace atmosphere. Proper respirator selection is an important component of an effective respiratory protection program. Accordingly, as per the Occupational Safety and Health Administration (OSHA) standards and specifications, APFs are necessary to protect employees who must use respirators to protect them from airborne contaminants. Hence, it is important to setup a facility for testing and certifying APFs for various types of respirators, which is currently unavailable.
The OSHA specifies that “respirator APF” and “maximum use concentration” (MUC), a term derived using APF, shall be an integral part of respiratory protection standard. MUC establishes the maximum airborne concentration of a contaminant in which a respirator with a given APF may be used. Operationally, the inhaled concentration can be estimated by dividing the ambient airborne concentration by the APF.
The use of particulate respirators (PRs) such as half face mask, full face mask, and powered air-purifying respirators (PAPRs) is essential for radioactive jobs in nuclear facilities to prevent/minimize any intake of radionuclide. Considering the prevention of internal exposure in nuclear facilities by effective respiratory protection program using suitable respirators, the PF Test Facility (PFTF) is essential for evaluating PF of various respiratory protective equipment. The technique employed to arrive at PF should meet the standards in the field of respiratory protection. With this impetus, the PFTF for testing and evaluating respiratory protective equipment meeting relevant applicable standards was designed, fabricated in-house, and installed at the Protective Equipment Laboratory of Health Physics Division. PFTF is developed as per the norms laid down by standard ISO 16900-1:2014.
| Materials and Methods|| |
PF is the ratio of concentration of aerosols outside (denoted as Co) the respirator and inside (denoted as Ci) the respirator volume, considering average breathing rate conditions. The setup consists of upper waist human dummy (mannequins) which is placed inside a glass test chamber. Test aerosols used for the certification of PRs may include sodium chloride (NaCl), di-octyl phthalate (DOP), and paraffin oil. These aerosols are generally assumed to be worst case surrogates for aerosols found in the workplace. DOP is considered a low hazard material (exposure limit of 5 mg/m3 and short-term exposure limit of 10 mg/m3), and it causes mild skin or eye irritation. Furthermore, it is classified by the ACGIH as a proven animal carcinogen with unknown relevance (suspected carcinogen) to humans and can be an environment hazard also. NaCl aerosol is now widely accepted as a respirator test particulate aerosol for qualifying (nonoily aerosols) respiratory filters. Hence, NaCl was selected and used as a test aerosol for studies for the certification of PRs as per the standard ISO 16900-1:2014.
Respirator under test is darn on a human dummy (mannequin), and a constant air flow of 20 lpm (equivalent to average industrial worker's breathing rate) is established through the test respirator using an air suction pump. Particle size distribution measurement (count median diameter) is carried out before and after filtration through test respirator by using optical particle counters (OPCs). Two identical iso-kinetic air sampling probes were used to draw air from outside (Co) and inside (Ci) the test respirator and fed to two identical OPCs, and aerosol size distribution data were acquired every 6 s simultaneously from the two OPCs (Grimm Make Dust Monitor Model 1.109 Version 12.30 with Firmware ID “F” by M/s GRIMM AEROSOL TECHNIK GmbH & Co. KG, AINRING, Germany) operated in multiplex mode. In multiplex operation mode (recommended for filter efficiency measurement purposes), the OPCs acquire aerosol size distribution data in the size range of 0.25–2 μm in 15 predefined size interval channels in fine size ranges represented by the aerosol median diameter of 0.25, 0.28, 0.3, 0.35, 0.4, 0.45, 0.5, 0.58, 0.65, 0.7, 0.8, 1.0, 1.3, 1.6, and 2.0 μm. The coarse size ranges from 1.6 to 20 μm in 8 or 16 channels. The acquired data from both the OPCs were analyzed for PF, using GRIM AEROSOL software provided by M/s GRIMM AEROSOL TECHNIK, AINRING GmbH & Co. KG, Germany. The test facility is designed based on constant air flow type, as it is important to mention that the effect of respiration type (viz., constant flow and cyclic flow) has no significant effect on the estimated PF. The PFTF was used to study air-purifying respirators such as PAPR, full face mask respirators, and half face mask respirators used in nuclear facilities.
The PFTF setup depicted in [Figure 1] (photograph along with its line sketch) shows the measurements carried out for a PAPR. The PAPR is placed on a mannequin inside a leak tight glass test chamber (420 L) connected to a setup for aerosol generation, injection and sampling, measurements using OPC, and data acquisition and analysis using GRIM software.
The salient features of the setup are described below:
- An aerosol generator containing aqueous 2% NaCl solution generates and pumps aerosols into the PFTF chamber. The concentration of aerosols is controlled using air flow, nebulizer feed pressure, and discharge rate
- The test chamber is operated under vacuum, and its vacuum is continuously monitored using well-type U-tube manometer. The test chamber is operated at 60 mmwg negative pressure to ensure that no aerosols will escape out of the chamber during the operation of PFTF chamber as an added safety feature. Other parameters monitored inside the chamber are humidity and temperature. There is a makeup air inlet to the chamber connected through high-efficiency particulate air (HEPA) filter. For better stability, NaCl aerosols require humidity in the chamber to be maintained between 45% and 50% relative humidity (RH). Aerosol studies show that aerosol concentration differs with RH. NaCl being a hygroscopic material in nature tends to absorb moisture. This affects particle size and its stability. Hence, a RH between 45% and 50% is chosen which maintains the maximum concentration of 0.3 μ particle size with higher stability
- There is an air circulation pump placed inside the chamber to homogenize the aerosol concentration inside the chamber
- To simulate breathing conditions, air is continuously drawn using an air suction pump in two streams from desired locations (inside and outside the respirator) at an average industrial worker's breathing rate of 20 lpm and fed to two individual sampling chambers. Aerosol concentration in these sampling chambers is measured using two identical OPCs connected to iso-kinetic sampling probes
- Aerosol concentration in sampled air Co and Ci is continuously recorded through GRIM AEROSOL software and analyzed for PF
- For accessing the chamber after collection of data, the chamber can be safely emptied of the injected aerosols using an air circulator placed in the chamber and provided with HEPA filters.
The following procedure is developed for the evaluation of PF for various kinds of respirators with due safety precautions including close watch on chamber vacuum, assessment of aerosol concentration in occupancy area, and filtration of chamber exhaust. The test procedure is indigenously developed as per the requirements of ISO standard 16900-1:2014 and OSHA standards.
- Place the darn mannequins (human dummy) with the respirator to be tested inside the test chamber, close the chamber, and start air circulation at desired flow rate, normally at 20 lpm
- Empty the test chamber of aerosols by filtered air purging (down to ambient aerosol concentration for all individual monitored particle sizes to <500 counts/L) and humidity in the test chamber to 50% RH (45% RH for sufficient operational margin)
- Inject NaCl aqueous aerosols into the test chamber till the desired aerosol concentration is reached. The NaCl test aerosols are dried by using in-built silicon cartridge as shown in [Figure 1] (PFTF) which is to be replaced periodically if there is a slight variation in silico n indicator granules, turning from dark blue to pink
- A typical aerosol buildup for 0.3 μm size aerosol in the test chamber with time is shown in [Figure 2]. It can be observed from [Figure 2] that, after a start of aerosol injection, aerosol concentration in the chamber quickly builds up and reaches fairly steady levels within 10 min from the start of injection of aerosols
- Data acquisition time region can be selected after 10 min of the start of aerosol injection
- Acquire both OPC readings through GRIMM software till sufficient data are generated (with data acquisition time set at every 6 s, in 5 min run duration, a set of 50 data is recorded). Save the data and stop aerosol generator. For tabulating the results, an average of 50 data points for five experiments was estimated for each respirator and presented in the respective table
- Start purging the test chamber by exhausting the aerosol-rich chamber air through HEPA filter. Continue the operation till aerosols of all test sizes reach background level. Stop the purging, and the test chamber is now safe to open
- Analyze the acquired data for PF for the desired range of particle sizes.
|Figure 2: Typical aerosol buildup for 0.3-μm size aerosol in the test chamber with time|
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| Experimental, Results and Analysis|| |
Study of aerosol generation in the test chamber
Typical case data acquired from OPC operated in multiplex mode in fine size ranges (0.25–2 μm in 15 channels), depicting aerosol buildup in the test chamber with time, are represented in [Figure 3]. It can be observed from the figure that, after a start of aerosol injection into the test chamber, the concentration of aerosol of all test sizes quickly builds up and reaches fairly steady levels from 8 to 10 min time. Hence, data acquisition time region is selected after 10 min from the start of aerosol injection.
|Figure 3: Typical aerosol buildup for aerosols of various sizes in the test chamber with time|
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The percentage count distribution of test aerosol in fine size ranges (0.25–2 μm in 15 channels) is presented in [Figure 4]. Almost 99% of the test aerosols are seen lying in the size range of 0.25–0.65 μm.
Evaluation of assigned protection factor of a half face mask particulate respirator
Half face mask particulate filter cartridge respirator, a tight fitting mask respirator, was darn on a mannequin (human dummy) as shown in the graphical representation in [Figure 5], for testing and evaluating PF. The sampling and analysis for PF were carried out as per the procedure, and the results of PF for 0.3-μm size particles are presented in [Table 1].
|Table 1: Protection factor of a half face mask particulate filter cartridge respirator|
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Measurements indicate that the PF obtained for the half face mask respirator for 0.3-μm size particles is 14.15 as against the specified value of 10 by the OSHA standards for half face mask particulate cartridge respirators.
Evaluation of protection factor of a full face mask particulate respirator
Measurements were carried out for evaluating PF of a full face (tight fitting) mask particulate cartridge respirator as shown in the graphical representation in [Figure 6]; the respirator was darn on a human dummy (skin-equivalent soft latex rubber human face) with a provision for sampling from respirator mask cavity. After placing the human dummy inside the test chamber, the chamber was emptied and NaCl test aerosols were fed into the chamber and measurements were made as per the procedure. The results are presented in [Table 2].
Measurements indicate that the PF obtained for full face mask respirator for 0.3-μm size particles is 112 as against the specified value of 100 given by the OSHA standards for full face mask particulate cartridge respirators.
Evaluation of protection factor of a powered air-purifying respirator
A battery-operated PAPR provides an integrated head, face, eye, and respiratory protection for 8 h continuous use conforming to the European standards (EN), offering a flow rate of 170 lpm (120 lpm minimum requirement as per EN norms) attached to a P3 type filter of 3000 cm2 surface area. The PAPR as shown in the graphical representation in [Figure 7] was darn on a mannequin (human dummy) for carrying out experiments. The sampling and estimation of PF were carried out as per the procedure and the results are presented in [Table 3].
Measurements indicate that the PF obtained for PAPR was 1328.37 as against the specified value of 1000 provided by the OSHA standards for PAPRs.
Protection factors of respirators with respect to particle size
The results obtained for various types of respirators for different particle sizes are presented in [Table 4]. Results of PF values obtained from the experiments for particulate filter half face mask, full face mask, and PAPR respirators are presented graphically in [Figure 8]. It is observed that particles of size more than 1.3 μm have least penetration for full face mask respirator. In addition, for particles >0.65 μm, PAPR respirator showed high PF values due to least penetration and leakage. As shown in [Figure 8], the PF for all respirators studied using this test facility was found lowest for particles ranging from 0.25 to 0.40 μm and found to be increasing for larger aerosol sizes above this range.
|Figure 8: Protection factor versus particle size for different respirators|
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| Conclusions|| |
- PFTF was developed and tested in-house successfully. Its operating procedure and methodology were established and found yielding consistent results for studies carried out for evaluating PFs for various types of particulate filter respirators
- PF for all respirators studied using this test facility was found lowest for 0.25–0.40 μm size particles and found to be increasing for larger aerosol sizes above this range
- A significant increase in the PF was observed for particle size of 0.7 μm and beyond for all the three types of respirators chosen for test
- The results obtained from the studies using standard NaCl aerosol have shown that the PF for the half face mask respirator is 14, for full face mask respirator it is 112, and for PAPR, it is 1328 for the aerosols having particle size distribution of 0.28–0.3 μm. The experiments confirm that the PRs selected for test conform to international standards
- The test facility is found to be useful for testing PFs for all types of air-purifying respirators used in BARC facilities.
The authors sincerely thank Dr. K. S. Pradeepkumar, Associate Director, HS and EG, for permitting us to establish the setup and carrying out necessary studies. Wholehearted support and endless efforts put up by Respiratory Protective Equipment Group staff in this endeavor has made this setup and study successful.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]
[Table 1], [Table 2], [Table 3], [Table 4]