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Broken Wafer Airborne Testing at 

Executive Summary:

On December 2, 2010 the National Institute for Occupational Safety and Health published a draft 

document entitled “NIOSH Current Intelligence Bulletin: Occupational Exposure to Carbon 

Nanotube and Nanofibers”. 

Based upon dose response data from animal studies, a recommended exposure limit (REL) has been 

established to protect workers’ health. The REL is based on the available subchronic and shortterm animal dose-response data of early-stage fibrotic and inflammatory lung responses to CNT 

exposure. Benchmark dose (BMD) estimates from the animal data (and the 95% lower confidence 

limit estimates of the BMD) have been extrapolated to humans by accounting for species 

differences in alveolar lung surface area. Working lifetime exposure concentrations have been 

calculated based on estimates of either the deposited or retained alveolar lung dose of CNT 

assuming an 8-hour time-weighted average (TWA) work shift exposure during a 40-hour work 

week, 50 weeks per year, for 45 years. 

In this risk analysis, NIOSH has determined that workers may be at risk of developing adverse 

respiratory health effects if exposed for a working lifetime at the upper limit of quantitation (LOQ) 

of NIOSH Method 5040, currently the recommended analytical method for measuring airborne 

CNT. The LOQ for NIOSH Method 5040 is 7 μg/m3. Specifically, the animal data-based risk 

estimates indicate that workers may have >10% excess risk of developing early-stage pulmonary 

fibrosis if exposed over a full working lifetime at the upper LOQ for NIOSH Method 5040. Until 

improved sampling and analytical methods can be developed, and until data becomes available to 

determine if an alternative exposure metric to mass may be more biologically relevant, NIOSH is 

recommending a REL of 7 μg/m3 elemental carbon (EC) as an 8-hr TWA respirable mass airborne 

concentration. Occupational exposures to all types of CNT can be quantified by NIOSH Method 

5040 as airborne EC. While data from animal studies with CNF are more limited, physiochemical 

similarities between CNT and CNF and findings of acute pulmonary inflammation and interstitial 

fibrosis in animals exposed to CNF indicate the need to also control occupational exposure to CNF 

at the REL using Method 5040. 

Based upon the NIOSH REL, performed airborne testing to determine the exposure 

concentration potential for workers who could be exposed via a wafer breakage incident. This was 

done inside a closed 6” aluminum cylinder with a nitrogen purge on the inlet side and a SKC Leland 

Legacy pump on the output side. Samples were sent to 

for analysis via NIOSH Method 5040 for Elemental Carbon. The test results came back “NonDetectable” which suggests it was below the detection limit capability of the analytical equipment. 

To ensure the lab could detect the presence of carbon nanotubes via this method, prepared a 

sample with a known loading on the filter media of 5 to 8 ug/cm2. The sample results were 5.12 

ug/cm2, which confirmed the lab was capable of detecting carbon nanotubes via NIOSH 

Method 5040 for Elemental Carbon. 
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Process Description:

Sample 1: 

On December 10, 2010 at the facility we performed a broken wafer test. A 

100mm bare silicon wafer, with a substrate of 3000 angstroms of thermal oxide, was coated with 

~300nm of (carbon nanotubes and deionized water) using 

 A 6” (inner diameter) aluminum 

cylinder was constructed. Each end of the tube was sealed using an aluminum cover which was 

bolted in place. On each end of the cylinder a 1⁄4” 316 stainless steel Swagelok fitting was installed 

to allow for a nitrogen purge at the inlet side and a 1⁄4” piece of Tygon tubing attached to a SKC 

Leland Legacy pump on the output side. A 1⁄2” 316 stainless steel Swagelok fitting was installed on 

the top and center of the cylinder. Through this fitting a 1⁄2” piece of stainless steel rod was installed 

and on the inner portion of the cylinder, a curve piece of aluminum attached to the rod. This would 

allow for the wafer to be broken with minimal exposure to atmosphere. 

Figure 1- 6” Aluminum Cylinder Setup: 

On the input side of the cylinder, a nitrogen line was installed with a regulator and flow meter. The 

flow meter was set to a flow of 10 scfm (~5L/min). On the output side a piece of 1⁄4” Tygon tubing 

was attached, then a 37mm Quartz Fiber Filter with a Mixed Cellulose backing was installed. Off 

the other end of the filter another piece of 1⁄4” Tygon tubing was attached. This tubing was then 

attached to the SKC Leland Legacy pump. The pump was set to run at 5L/min. This entire setup 

was put inside an exhausted fume hood which had a face velocity of ~90 fpm. 

The 100mm CNT coated wafer was put inside the aluminum cylinder. The cylinder was then sealed 

and all connections made. A person wearing a NIOSH approved full-face P100 cartridge respirator 

then proceeded to break the wafer by using the 1⁄2” stainless steel rod with the curved piece of 

aluminum attached to it inside the cylinder. The person continued to break the wafer by moving 
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the rod up and down for ~1 min. This was repeated 3 more times over a 6 hour timeframe. At the 

end of six hours, the person shutoff the pump, removed and capped the filter. The aluminum 

cylinder was opened and a picture taken of the broken wafer (see figure 2 & 3). The total airflow 

through the filter was 1200L (5L/min x 240 minutes). 

Figure 2: Broken Wafer in Aluminum Cylinder 

Figure 3: Broken Wafer Outside of Aluminum Cylinder 
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Sample 2: 

On January 19, 2011 a second sample was prepared and run the same as Sample 1, with two notable 

differences; 1.) The filter cartridge used to collect the sample was a 37mm Quartz Fiber Filter with 

a Quartz backing instead of a Mixed Cellulose backing and 2.) The front portion of the filter was 

removed and installed inside the aluminum cylinder (open faced). This was done to allow a more 

uniform loading of the filter cartridge. Sample 1 was noted as having a black dot in the center of 

the filter, which we concluded was due to the 1⁄4” opening on the filter cartridge. By opening the 

front of the filter and exposing it inside the cylinder, a more uniform loading of the filter was 

anticipated. This sample was run for 21 hours. The total airflow through the filter was 6000L 

(5L/min x 1260 minutes). 

The below line drawing details the placement of the filter cassettes for Sample 1 vs. Sample 2. 

Sample 3: 

On January 19, 2011 a sample was prepared with a known quantity of CNT material. This was 

done to ensure was able to detect This sample was prepared by 
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A CNT suspension was created using 20mg of raw carbon nanotube material and 10g of DI water in 

a 20mL vial. The vial was taken to an exhausted fume hood where 100uL of Triton-X 100 were 

added. This mixture was sonicated for 3 hours, with the concentration of the resulting suspension 

being ~ 2mg/mL or 2ug/uL. 

The requested surface density of the CNT material using a 37mm Quartz Fiber filter with a quartz 

backing (or 11.6 cm2) was between 5 and 8 ug/cm2 of CNT. Thus the total mass of CNT material 

on the filter needed to be between 58-93ug. This quantity translates to a 29-46uL of our 2ug/uL raw 

material suspension. 

The filter suspension was prepared by adding 46 μL of our 2μg/μL raw material suspension to 20 

mL of water. The optical density of the resultant suspension was 0.135 @ 550 nm. The filter 

suspension was then loaded into a 60 mL Teflon syringe and subsequently pushed through the 

provided capture filter. The effluent optical density was collected and determined to be 0.057 @ 

550 nm. Thus, 58 % percent of the material passed through the filter was retained (i.e., 54 ug). 

While filter retention was low, only ~60% of the filter area (mostly in the center) was stained by the 

influent CNTs. Given the retention and the surface area of the filter covered, the darkened areas 

should contain ~7.7 ug/cm2 of CNTs. 

Results:

All samples were analyzed using NIOSH Method 5040 for Elemental Carbon at 

at their facility. A Lab OC-EC Aerosol Analyzer (thermal optical analyzer) was 

used to evaluate the samples, with the results being reported as OC (ug/sq cm) and EC (ug/sq cm). 

 is only reporting the EC results. Note: ND = Non-Detectable (See Table 1) 

Table 1: NIOSH Method 5040 Airborne Results 

Conclusions:

Sample 3 was confirmation showing is capable of detecting carbon 

nanotubes via their analytical equipment. Based upon this, a 100mm broken wafer coated with 

~300nm of solution using both 

Sample 

#

Sample Description Date 

Sample 

Taken

Type of Filter Total Air 

Flow 

(L/min)

Date of 

Results

EC 

(ug/sq cm)

1 Broken Wafer w filter outside of 

cylinder

12/22/10 37mm QFF w/ 

Cellulose back

1200 1/6/11 ND

2 Broken Wafer with filter inside 

of cylinder

1/19/11 37mm QFF w/ 

Quartz back

6300 1/27/11 ND

3 Filter loading with known CNT 

quantity

1/19/11 37mm QFF w/ 

Quartz back

NA 1/27/11 5.21
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corresponding to substance , has a non-detectable limit for Elemental Carbon via NIOSH 

Method 5040 for Elemental Carbon.