Application of direct-reading and elemental carbon analysis methods to measure mass-based penetration of carbon nanotubes through elastomeric half-face and filtering facepiece respirators

Figures & data

Table 1. Mass-based SWCNT and MWCNT penetrations through FFRs and EHRs measured using direct-reading and elemental carbon analysis methods.

			SWCNT penetrations measured by direct-reading and EC methods		MWCNT penetrations measured by direct-reading and EC methods
Respirator type	Class of filter	Respirator model	SWCNT penetration^a by direct-reading method (%)	SWCNT penetration^a by EC method (%)	MWCNT penetration^a by direct-reading method (%)	MWCNT penetration^a by EC method (%)
FFRs	N95	N95-A	0.23 ± 0.06	0.18 ± 0.06	0.11 ± 0.03^c	0.04 ± 0.01
		N95-B	0.48 ± 0.16	0.29 ± 0.09	0.15 ± 0.05^c	0.05 ± 0.01
	P100	P100-A	0.009 ± 0.002^b	0.007 ± 0.002	0.005 ± 0.002^c	0.004 ± 0.001
		P100-B	0.012 ± 0.003^b	0.008 ± 0.002	0.007 ± 0.002^c	0.005 ± 0.002
EHRs	N95	N95-A	1.09 ± 0.36	0.69 ± 0.23	0.21 ± 0.07^c	0.13 ± 0.04
		N95-B	0.88 ± 0.25	0.40 ± 0.14	0.18 ± 0.05^c	0.12 ± 0.04
	P100	P100-A	0.019 ± 0.007^b	0.014 ± 0.005	0.009 ± 0.002^c	0.008 ± 0.003
		P100-B	0.017 ± 0.006^b	0.011 ± 0.003	0.008 ± 0.002^c	0.006 ± 0.002

^a Mean value ± relative standard deviation (n = three replicate tests);

^b significantly different from SWCNT penetration data in the EC analysis method for the P100-respirator class;

^c significantly different from MWCNT penetration data in the EC analysis method for both: the P100-respirator class and the combination of N95- and P100-respirator classes.

Figure 1. Schematic diagram of CNT-ARTS, including direct-reading instruments (SMPS-APS systems 1 and 2) and a sample collection system for the EC analysis method: apparatus for upstream sample (filter cassette, 1A; mass flow meter, 1B; air regulator, 1C; in-house vacuum, 1D), apparatus for downstream sample (filter cassette, 2A; flow meter, 2B; air regulator, 2C; vacuum, 1D), and a constant airflow system (HEPA filter, 3A; flow meter, 3B; air regulator, 3C; vacuum, 3D).

Figure 2. Size distribution of airborne SWCNTs (solid line) and MWCNTs (dashed line) in the testing chamber measured using the combined SMPS-APS method.

Figure 3. TEM images of the upstream and downstream CNT particles: upstream aerosolized SWCNT particles collected in the test chamber (a); downstream SWCNT particle collected inside the respirator (b); upstream aerosolized MWCNT particles (c); downstream MWCNT particle (d).

Figure 4. Mean SWCNT and MWCNT penetrations (mass-based penetration; n = 3 for each model) through the tested FFRs and EHRs as a function of individual particle size measured using the SMPS-APS method.

Table 2. Sample calculations of upstream and downstream EC concentrations (µg/m³).

FFR model	CNT sample	Flow rate (LPM)	Sampling time (min)	EC on the sample portion (µg/cm^2)^a	Total EC (CNTs) on filter (µg)^b	CNT concentration (µg/L)^c	CNT concentration (µg/m^3)^d
N95 FFR	Upstream	0.5	3	3.49	29.84	19.89	19,890
	Downstream	3.0	90	0.93	7.95	0.03	30

^a Blank corrected EC results (µg/cm²) for a 1.5 cm² punch from the filter;

^b total EC on filter calculated as: (EC on sample portion, µg/cm²) x total deposit area of the filter (8.55 cm²);

^c CNT concentration: total EC on filter per liter of sampled air;

^d all upstream and downstream EC data were converted to mass per cubic meter air (µg/m³).