Unknown Gases 

Generated from a 

Silicon Wafer Grinding 

Filtration Process – 

Colorado

Srinivas Durgam, MSPH, MSChE, CIH

Robert Streicher, PhD

Health Hazard Evaluation Report

HETA 2008-0045-3145

November 2011 

DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

Workplace

Safety and Health

 National Institute for Occupational 

Safety and Health
The employer shall post a copy of this report 

for a period of 30 calendar days at or near 

the workplace(s) of affected employees. The 

employer shall take steps to insure that the 

posted determinations are not altered, defaced, 

or covered by other material during such 

period. [37 FR 23640, November 7, 1972, as 

amended at 45 FR 2653, January 14, 1980].
Health Hazard Evaluation Report 2008-0045-3145 Page i

Report Abbreviations................................................................................................ii

Highlights of the NIOSH Health Hazard Evaluation........................iii

Summary .........................................................................................................v

Introduction ...................................................................................................1

Assessment.....................................................................................................4

Results..............................................................................................................6

Discussion.................................................................................................... 11

Conclusions................................................................................................. 13

Recommendations.................................................................................... 13

References.................................................................................................... 14

Contents

Acknowledgments Acknowledgments and Availability of Report................................ 25

Appendix A Methods........................................................................................................ 16

Appendix B Occupational Exposure Limits & Health Effects............................. 17

Appendix C Tables............................................................................................................. 22
Page ii Health Hazard Evaluation Report 2008-0045-3145

Abbreviations

ACGIH® American Conference of Governmental Industrial Hygienists

CFR Code of Federal Regulations

CO Carbon monoxide

CO2 Carbon dioxide

GA General area

GC-MS Gas chromatography-mass spectrometry

GC-TCD/FID Gas chromatography-thermal conductivity detector/flame ionization detector

HHE Health hazard evaluation

H2 Hydrogen

IDLH Immediately dangerous to life or health

LOD Limit of detection

LOQ Limit of quantitation

mg/m3 Milligrams per cubic meter

mm Millimeter

NAICS North American Industry Classification System

ND Not detected

NIOSH National Institute for Occupational Safety and Health

OEL Occupational exposure limit

OSHA Occupational Safety and Health Administration

PBZ Personal breathing zone

PPE Personal protective equipment

PEL Permissible exposure limit

ppm Parts per million

REL Recommended exposure limit

STEL Short-term exposure limit

TLV® Threshold limit value

TWA Time-weighted average

WEELTM Workplace environmental exposure level
Health Hazard Evaluation Report 2008-0045-3145 Page iii

The National Institute 

for Occupational Safety 

and Health (NIOSH) 

received a request for a 

health hazard evaluation 

at a semiconductor 

manufacturing plant in 

Colorado. The employer 

submitted the request 

because unknown gases 

had pressurized and 

heated a covered 55-

gallon metal storage 

drum (“drum”) containing 

used filters from a silicon 

wafer grinding filtration 

process. The company 

was concerned that the 

disposal of used filters 

in covered drums could 

pose a health and safety 

hazard for its employees.

Highlights of the

NIOSH Health

Hazard Evaluation

What NIOSH Did

● We visited the plant in February 2008 and March 2009.

● We collected air samples in the filtration process area and 

from the inside of covered drums. We sampled for hydrogen, 

carbon monoxide, and carbon dioxide.

● We reviewed the company’s air sampling records, including 

sampling for silane.

● We spoke with the maintenance employees about their 

symptoms.

What NIOSH Found

● Hydrogen was measured at concentrations up to 118,000 

parts per million inside the covered drums.

● Carbon monoxide and carbon dioxide were also found inside 

the covered drums.

● Silane was measured at concentrations of 20 to 50 parts per 

million inside a covered drum.

● Maintenance employees reported no symptoms related to 

their work that would suggest high exposures to carbon 

monoxide.

● Disposing of used filters from the silicon wafer grinding 

filtration process in covered drums can pose a health and 

safety hazard for employees.

What Managers Can Do

● Leave the drums uncovered to prevent the buildup of gases.

● Post signs in the work area to remind employees not to cover 

the drums.

What Employees Can Do

● Leave the drums uncovered.

● Report all symptoms, including headache, nausea, or 

confusion to the on-site healthcare professional.
Page iv Health Hazard Evaluation Report 2008-0045-3145

NIOSH was asked to 

identify unknown gases 

accumulating in a covered 

drum that contained 

used filters from the 

silicon wafer grinding 

filtration process. We 

measured H2, CO, and 

CO2 inside the covered 

drums. The concentration 

of H2 increased with 

time inside the covered 

drums. Disposing of used 

filters from the silicon 

wafer grinding filtration 

process in covered 

drums can pose a health 

and safety hazard to 

employees. Leaving the 

drums uncovered will help 

reduce this hazard. 

Summary

NIOSH received a request from an employer representative for 

an HHE at a semiconductor manufacturing plant in Colorado. 

The request concerned unknown gases that were pressurizing 

and heating a covered 55-gallon metal storage drum (“drum”) 

containing used filters from a silicon wafer grinding filtration 

process. The requestor was concerned that disposing of these used 

filters in covered drums may present a safety and health hazard to 

maintenance employees working in the filtration process area. No 

health effects among maintenance employees were listed in the 

request.

We visited the plant in February 2008 and March 2009. We 

collected PBZ, GA, and task-based air samples for H2, CO, and 

CO2. We analyzed the samples with different sampling and 

analytical measurement techniques. We spoke with maintenance 

employees about their symptoms and reviewed the company’s 

previous air sampling reports.

We found that H2 was being generated inside the covered drums 

and that the concentrations increased with time. We also measured 

CO and CO2 inside the covered drums, but these concentrations 

varied drastically depending on the analytical method, making 

interpreting the results difficult. Employee PBZ exposure to CO 

could exceed the NIOSH ceiling limit and ACGIH excursion limit 

when employees evaluate the covered drums for off-gassing filters 

prior to disposal. Our results indicate that a possible hazard from 

CO exposure might exist. This hazard can be easily mitigated by 

keeping the drums uncovered to prevent the buildup of gases. 

Maintenance employees reported no symptoms related to their 

work that would suggest high exposures to CO.

On the basis of a scientific literature review and air sampling 

results, we conclude that the covered drums were pressurized 

primarily because of H2 formation and that silane was also formed. 

The disposal of used filters resulting from the silicon wafer 

grinding filtration process in covered drums can pose a health 

and safety hazard to employees. Leaving the drums uncovered will 

help mitigate these hazards. In addition, if employees experience 

headache, nausea, or confusion, they should promptly report them 

to the on-site healthcare professional.

Keywords: NAICS 334413 (Semiconductor and Related Device 

Manufacturing), silicon, silane, hydrogen, carbon monoxide, CO, 

carbon dioxide, CO2, wafer grinding
Health Hazard Evaluation Report 2008-0045-3145 Page 1

Introduction

NIOSH received a request from an employer representative for 

an HHE at a semiconductor manufacturing plant in Colorado. 

The request concerned unknown gases that were pressurizing 

and heating a covered 55-gallon metal storage drum (“drum”) 

that contained used filters from a silicon wafer grinding filtration 

process. The requestor was concerned about the safety and health 

of the maintenance employees working near the filtration process 

as a result of exposure to this unknown gas. No health effects 

among maintenance employees were listed in the request.

In October 2006 a maintenance employee removed clogged filters 

from the silicon wafer grinding filtration process that were warm to 

the touch. Because this was an odd occurrence, the maintenance 

employee called the company industrial hygienist to ask how to 

dispose of the used filters. He was instructed to place the filters 

in a drum and to move the drum outside until the industrial 

hygienist could evaluate the situation. The employee followed 

these instructions but sealed the drum with a rigid lid. When 

the company industrial hygienist arrived, he removed the lid of 

the drum while wearing PPE (a fully encapsulated suit with a 

self-contained breathing apparatus). When the seal to the lid was 

loosened, the lid violently “popped” off the drum a reported 5 

feet into the air. No one was injured but the incident did reveal a 

possible explosion hazard for the maintenance employees.

Following this incident the company industrial hygienist 

attempted to identify the gases in the drum containing used 

filters. These attempts included sampling the air inside the drum 

with a colorimetric detector (ChemKeyTM TLD toxic gas detector, 

Honeywell Analytics, Lincolnshire, Illinois) after it was covered with 

a shower cap and allowed to sit overnight; air sampling for arsine 

using NIOSH Method 1003 and phosphine using NIOSH Method 

6001; and air sampling for CO and hydrogen sulfide using direct 

reading instruments. The company industrial hygienist concluded 

that H2 was present along with some type of hydride gas.

We visited the plant February 6–7, 2008, to learn more about the 

process, observe work practices, and conduct air sampling to identify 

the unknown gases inside covered drums. We returned on March 

17–19, 2009, to evaluate potential employee exposures to CO.
Page 2 Health Hazard Evaluation Report 2008-0045-3145

Facility and Process Description

The company manufactured a variety of microelectronic devices 

including radiofrequency integrated circuits and transistors. Silicon 

wafers, an integral part of these devices, are obtained by cutting a 

single crystal silicon ingot. These wafers can range up to 10 inches 

in diameter and are ground to a thickness of 0.07 mm [Burgess 

1995].

The backs of the silicon wafers are wet-ground in an enclosed 

machine with deionized water. The water stream containing 

elemental silicon is sent to a 1,500-gallon storage tank in the 

basement of the building. The silicon particles are removed from 

the water with bag filters and polypropylene cartridge filters. Of 

the four cartridge filter tanks and four bag filter tanks, only half are 

operational at any one time. The alternate filters are used when the 

first set of filters become clogged.

A portion of the filtered water was recirculated to the storage tank, 

and the rest was discharged. Maintenance employees removed both 

types of filters on the basis of filter back pressure and the amount 

of water being discharged. The clogged filters were placed in a 

nearby uncovered drum.

The company industrial hygienist monitored the drum with a 

ChemKey TLD toxic gas detector, a direct reading instrument 

with a colorimetric detector to identify whether the filters are offgassing. The company had ChemKeys that allowed the instrument 

to detect and provide quantitative air concentrations for arsine 

and phosphine. These ChemKeys were chosen for two reasons: 

the detection limit for arsine is lower than for phosphine and 

silane, thus allowing detection of hydride at lower levels; and arsine 

and phosphine gas are filtration byproducts generated during 

the grinding of arsenic- and phosphorous-doped silicon wafers, 

which are also manufactured at this plant. The drum was covered 

overnight with a plastic shower cap, and air samples were taken the 

following morning. If the instrument detected gas above the PEL 

for arsine of 0.05 ppm (lower than the phosphine PEL of 0.3 ppm), 

the drum was uncovered, allowed to off-gas for another 2–3 weeks, 

and rechecked. If the gas concentrations were below 0.05 ppm, the 

drum was sealed with a rigid lid and shipped to a contractor for 

disposal in a landfill.

Introduction

 (continued)
Health Hazard Evaluation Report 2008-0045-3145 Page 3

Introduction

 (continued)

Figure 1. Silicon wafer grinding 

filtration process.

Figure 2. Used cartridge and bag 

filters in a 55-gallon metal 

storage drum.

Figure 3. Used and new cartridge filters 

(Courtesy: Company photo).
Page 4 Health Hazard Evaluation Report 2008-0045-3145

Assessment

February 2008 Site Visit 

We met with the employer and employee representatives to discuss 

the HHE request. We spoke with employees and observed the 

silicon wafer grinding process, the associated water filtration 

system, employee work practices, and workplace conditions.

During our visit, a maintenance technician drained the water from 

the bag and cartridge filter tanks. After waiting approximately 

a half hour, the technician opened the tops of the bag filter 

and cartridge tanks. We immediately collected air samples with 

Vacutainers® (evacuated glass tubes) from inside two of the three 

cartridge tanks. The filters were removed, placed in a drum, 

covered with a plastic shower cap, and sealed with tape.

We collected vacutainer air samples from inside the covered drums 

that contained filters removed on January 18, 2008, and February 

7, 2008, in the area around the filtration process, and in office 

areas on a different floor. We also monitored the temperature 

inside the covered drum that contained used filters from February 

7, 2008. We reviewed air sampling reports dated November 

7, 2006, and June 18, 2007, for evaluations conducted by a 

consultant who was trying to identify the unknown gas.

Figure 4. Collecting an air sample from 

inside a covered 55-gallon 

metal storage drum that 

contained filters removed on 

February 7, 2008.
Health Hazard Evaluation Report 2008-0045-3145 Page 5

Assessment

 (continued)

Figure 5. Collecting a vacutainer air 

sample from inside a covered 

55-gallon metal storage drum.

Analysis of the vacutainer air samples from this visit indicated high 

concentrations of H2, CO, and CO2 inside the covered drums. 

These findings prompted us to return to the plant in March 2009 

to further evaluate CO and CO2 exposures.

March 2009 Site Visit

We measured airborne CO concentrations in the PBZ of the 

maintenance employees and the plant industrial hygienist as 

well as in various areas of the plant with three different direct 

reading monitors. On March 18, 2009, we measured temperature 

with a digital thermometer (Fisher Scientific Traceable® 

Jumbo Display Thermometer, Thermo Fisher Scientific Inc., 

Pittsburgh, Pennsylvania) and CO concentrations inside two 

covered drums containing filters removed on March 12, 2009, 

and March 18, 2009, with one or more sampling techniques: 

vacutainers, colorimetric gas detection tubes, and a Dräger Pac 

III direct reading CO monitor (Dräger Safety Inc, Pittsburgh, 

Pennsylvania). Vacutainers were also analyzed for H2, CO, and 

CO2 by the NIOSH contract laboratory, and a duplicate set of 

samples was analyzed for CO and CO2 by the OSHA Salt Lake 

Technical Center. We evaluated the full-shift CO exposure of the 

maintenance technician (which included conducting a filter change 

out) using three different direct reading instruments. During this 

visit, the company industrial hygienist collected air samples for 

silane with colorimetric gas detection tubes.
Page 6 Health Hazard Evaluation Report 2008-0045-3145

At the end of the day on March 18, 2009, both drums (which 

contained filters from March 12 and 18, 2009) were covered with 

plastic shower caps and left overnight to simulate conditions 

under which they would be checked by the company industrial 

hygienist for off-gassing prior to disposal. On March 19, 2009, 

we collected vacutainer air samples from the inside of both 

drums, and we also collected task-based PBZ air samples when the 

industrial hygienist was checking the drums.

Details on the methods used in this evaluation for H2, CO, and 

CO2, are explained in Appendix A. The OELs and potential 

health effects from H2, CO, CO2, and silane are discussed in 

Appendix B.

Assessment

 (continued)

Results

Detailed PBZ, GA, and task-based air sampling results for H2, CO, 

and CO2 are presented in Tables C1–C6 of Appendix C.

February 2008 Site Visit

Table C1 presents the vacutainer air sample data collected from 

the inside of cartridge tanks 1 and 2; the inside of a covered 

drum containing filters from January 18, 2008; and in various 

areas of the plant. The concentrations from inside the cartridge 

tanks ranged from < LOQ to 64,500 ppm for H2, 3,500 to 22,400 

ppm for CO, and 3,400 to 17,000 ppm for CO2. The highest 

concentrations were found when a maintenance technician opened 

cartridge tank 1; the lowest were from cartridge tank 2. The 

concentrations from inside the covered drum containing filters 

from January 18, 2008, were ND (< 5,000 ppm) and 26,200 ppm 

for H2; 2,200 and 7,500 ppm for CO; and < LOQ and 5,900 ppm 

for CO2. Although the drum cover was not removed, the lower 

concentration for all three gases was from the second air sample 

collected from inside the drum, approximately 1 minute after 

the first air sample. The vacutainer air samples collected in the 

basement near the process area and on the second floor of the 

building were all below the LOD.

Table C2 presents the vacutainer air sample data collected from 

the inside of another covered drum containing filters removed on 

February 7, 2008. Thirteen vacutainer air samples were collected 

over approximately 4 hours. The concentrations ranged from ND 

to 84,700 ppm for H2; ND to 19,900 ppm for CO; and ND to 
Health Hazard Evaluation Report 2008-0045-3145 Page 7

Results

 (continued) 16,700 ppm for CO2

. As displayed in Figure 6, H2 concentrations 

inside the covered drum fluctuated but increased over time and 

reached 84,700 ppm at the end of the sampling period. The 

concentrations of CO and CO2 did not increase over time, but 

did seem to mimic each other (i.e., an increase in CO reflected 

an increase in CO2). Both CO and CO2 approached 20,000 ppm 

at the beginning of the sampling period but were not detected at 

the end of the sampling period. Temperature readings taken along 

with each vacutainer air sample indicated an overall temperature 

increase of 3.0oF.

Figure 6. Time plot of H2, CO, and 

CO2 concentrations inside 

a covered 55-gallon metal 

storage drum containing 

filters removed on February 

7, 2008.

March 2009 Site Visit

Table C3 presents the vacutainer air sample data collected from 

the inside of bag filter and cartridge tanks, from the inside of 

a covered drum containing filters from March 12, 2009, and 

from the basement. The concentrations inside the bag filter and 

cartridge tanks ranged from < LOQ to 15,800 ppm for CO and 

ND to 8,930 ppm for CO2; H2 was not detected. The CO and CO2

concentrations varied between bag and cartridge tanks and did not 

show a trend within each tank (e.g., bag filters did not always have 

the highest CO or CO2 concentration nor did an elevated CO 

concentration in a cartridge tank have a corresponding elevated 

CO2 concentration). The concentrations from inside the covered 

drum containing filters from March 12, 2009, ranged from < LOQ 
Page 8 Health Hazard Evaluation Report 2008-0045-3145

to 34,000 ppm for H2, 5,280 to 19,400 ppm for CO, and 3,750 to 

15,000 ppm for CO2

. Although the drum cover was not removed, 

the highest H2

 concentration was from the last vacutainer air 

sample collected from this drum; in contrast, the CO and CO2

concentrations decreased over time. The first vacutainer air sample 

collected in the basement near the process area found all three 

gases, but the second air sample (collected immediately after the 

first) identified only CO.

Table C4 presents data from 15 vacutainer air samples collected 

over a 5-hour period from inside a covered drum containing 

filters from March 18, 2009. The concentrations ranged from 

ND to 118,000 ppm for H2

; ND to 21,600 ppm for CO; and ND 

to 18,800 ppm for CO2

. The results displayed in Figure 7 show 

similarities to those in our previous visit. The H2

 concentrations 

increased over time (118,000 ppm at the end of sampling), and 

CO and CO2

 concentrations mimicked each other; both had 

peak concentrations around 20,000 ppm. Temperature readings 

taken along with each vacutainer air sample indicated an overall 

temperature increase of 14.5oF.

Results

 (continued)

Figure 7. Time plot of H2, CO, and 

CO2 concentrations inside 

a covered 55-gallon metal 

storage drum containing filters 

removed on March 18, 2009.

Figure 8 presents CO concentrations inside a covered drum 

containing filters from March 18, 2009. In addition to CO data 

from vacutainer air samples analyzed using GC-TCD/FID (data 

presented in Table C4 and Figure 7), Figure 8 presents data from 

vacutainer air samples analyzed by GC-MS, colorimetric detection 
Health Hazard Evaluation Report 2008-0045-3145 Page 9

tubes, and a Pac III direct reading instrument. The OSHA Salt 

Lake Technical Center analyzed the duplicate vacutainer air 

samples via GC-MS and reported all CO concentrations as less 

than 100 ppm and CO2

 concentrations as approximately 400 ppm. 

Of the six colorimetric detection tube air samples collected during 

this period, the concentration of CO inside the covered drum 

ranged from 8 to 40 ppm. The Pac III measurements showed an 

increase in CO concentrations over time that ultimately reached 

the upper limit of the instrument (10,000 ppm).

In addition to the CO air samples we collected inside a covered 

drum containing filters from March 18, 2009, the company 

industrial hygienist collected air samples for silane inside the same 

drum with a colorimetric detection tube (Sensidyne, Mülheim, 

Germany). The colorimetric detection tubes showed silane 

concentrations ranging from 20 to 50 ppm. The inside of the drum 

was also sampled using a ChemKey TLD toxic gas detector that 

showed that hydride gases were present.

Table C5 presents vacutainer air sample data from two covered 

drums containing filters from March 12 and March 18, 2009. 

Both drums were left covered overnight and air samples were 

collected on March 19, 2009. The concentrations inside the drum 

containing filters from March 12, 2009, ranged from 13,900 to 

25,400 ppm for H2

; ND to 21,400 ppm for CO; and ND to 18,600 

ppm for CO2

. The concentrations inside the drum containing 

filters removed on March 18, 2009, ranged from 138,000 to 

153,000 ppm for H2

; 643 to 2,900 ppm for CO; and ND to 

< LOQ for CO2

.

Figure 8. Time plot of CO 

concentrations measured 

using different analytical 

methods inside a covered 

55-gallon metal storage drum 

containing filters removed on 

March 18, 2009.

Results

 (continued)
Page 10 Health Hazard Evaluation Report 2008-0045-3145

On March 18–19, 2009, using three different direct reading 

instruments, we evaluated the full-shift CO exposure of a 

maintenance technician who conducted a filter change out. We 

also evaluated the CO and H2

 exposures of the company industrial 

hygienist while he was checking drums prior to disposal (Table C6). 

The CO measurements of the maintenance technician did not 

exceed applicable OELs. The peak CO measurement was 29 ppm, 

which is well below the NIOSH ceiling limit of 200 ppm. This air 

concentration was recorded when the technician had left the filter 

change out process area to complete other routine tasks. All three 

instruments’ CO concentration measurements were consistent 

with each other. Two of three direct reading instruments showed 

peak CO measurements for the company industrial hygienist that 

exceeded the NIOSH ceiling limit of 200 ppm for CO, and all 

three exceeded the ACGIH excursion limit of 125 ppm. We also 

collected two PBZ air samples with vacutainers during this task; 

one showed the presence of CO at a concentration below the LOQ 

(228 ppm), and the other did not detect CO above the LOD of 

100 ppm.

Document Review

The company suspected that a hydride gas caused the October 

2006 incident, so they asked the consultant to sample for silane 

and phosphine inside the covered drums and workplace air. Air 

sampling for phosphine (four GA air samples) was conducted 

using OSHA Method 1003. Silane (four GA air samples) was 

sampled using an in-house method developed by the consultant. 

This method consisted of a 37-mm mixed cellulose ester 

prefilter in line with an impinger containing a 0.01N potassium 

hydroxide solution. The air samples were analyzed to detect 

the presence of silicon using inductively coupled argon plasmamass spectrometry. Silane was detected in the air samples, but 

phosphine air concentrations were not detected above an LOD 

of 0.030 ppm. Silicon, however, was detected in the field blank 

sample, and the consultant attributed it to silicon possibly being 

etched from the glass impinger. The consultant recommended 

further investigation to determine if the unknown gas was truly 

silane.

The consultant also performed drum and GA air sampling in 

May 2007 with Teflon® impingers (instead of glass) and the 

same sampling and analytical methods. Silane concentrations 

Results

 (continued)
Health Hazard Evaluation Report 2008-0045-3145 Page 11

inside a covered drum were 0.99 mg/m3 and 0.12 mg/m3, 

and the silane concentrations in two comparison air samples 

collected in a room south of the silicon wafer grinding 

process were 0.029 mg/m3

 and 0.024 mg/m3. Because 

the air concentrations were below applicable OELs no 

recommendations were made.

Discussion

Results

 (continued)

Crystalline silicon doped with different elements is a base 

semiconducting material for many electronic products. Upon 

grinding, crystalline silicon ingots produce fine silicon powder, 

which has a high surface area. Theoretically, silicon reacts with water 

to produce silicon dioxide (silica) and hydrogen, and this reaction 

(wet oxidation) can be expected to occur during the wet grinding 

process, as shown below [Doremus and Breed 1976; Stephen and 

Riley 1989; Chemguide 2010; Gatech 2010].

It is possible that some silicon can react with the generated 

hydrogen gas to form silane as shown above. Experiments involving 

the reaction of water vapor with freshly cleaved, etched, or polished 

silicon surfaces have shown silane in ppm concentrations [Lampert 

et al. 1986]. Salonen et al. studied the oxidation of porous silicon 

in water, methanol, and ethanol. Silane was not detected when 

porous silicon reacted with water. However, the reaction of porous 

silicon with methanol and ethanol showed traces of silane, and 

pressurization of glass ampoules used in the experiments was also 

observed [Salonen et al. 1997]. Silane is a pyrophoric gas that poses 

a severe explosion hazard [ACGIH 1989].

Our air sampling of the drums showed that H2

 gas was being 

generated, and the concentrations increased with time inside a 

covered drum. The increasing H2

 concentrations inside a tightly 

sealed drum could cause it to become pressurized. Additionally, 

the drum temperature increased over time, suggesting exothermic 

chemical reactions inside the drum. The presence of silane is 

theoretically possible and was shown by air sampling (impinger and 

colorimetric tube) conducted by the company industrial hygienist. 

The presence of a pyrophoric gas such as silane and a combustible 

gas such as H2

 in the same covered drum could be a safety hazard. 
Page 12 Health Hazard Evaluation Report 2008-0045-3145

This hazard could be easily minimized by ensuring that the drums are 

left uncovered at all times thus preventing a buildup of such gases.

In our first site visit, we were surprised to measure high CO and 

CO2

 concentrations inside the covered drums because there was no 

apparent source to generate these gases. However, the concentrations 

reported in the tables are not indicative of employee PBZ exposures. 

The different measurement and analysis techniques we used 

during the second site visit did not clarify whether CO and CO2 

were truly present as our results continued to show a wide range 

of concentrations. The high CO concentrations measured with the 

Pac III direct reading instrument tended to agree more with the 

vacutainer air samples analyzed with GC-TCD/FID. These results, 

however, conflicted with the low CO concentrations detected on 

the colorimetric gas detection tubes and the vacutainer air samples 

analyzed with GC-MS by the OSHA Salt Lake Technical Center.

An additional challenge in interpreting our direct reading CO 

results is that many of the chemical-specific sensors can positively 

or negatively bias the readings in the presence of interfering gases 

or when measuring a gas mixture. For the Pac III, the manufacturer 

indicated that a CO sensor in a H2

-only environment can have up 

to a 40% positive bias, i.e., in an atmosphere containing only H2

 at 

1,000 ppm, the instrument will indicate a CO concentration of up 

to 400 ppm [Walker 2011]. Similarly, the Biosystems ToxiUltra has 

a 40% positive bias, and BW Technologies reports a 20% positive 

bias for its CO sensors [Biosystems 2011; Heckathorn 2011]. 

Therefore, the presence of H2

 could have affected our direct reading 

CO results. In addition, the manufacturers were not aware of the 

sensors’ biases when measuring gas mixtures, making it difficult to 

interpret the instrument readings.

The vast difference in the gas concentrations measured by different 

analytical and measurement techniques makes it difficult to have 

confidence in the results, especially the high CO concentrations. 

In addition, employees working near the process and conducting 

tasks such as removing cartridge tank filters reported no health 

symptoms such as headaches and nausea that might indicate high 

CO exposures. However, there is not sufficient evidence to suggest 

the CO concentrations found should be disregarded.

Because H2

 was present inside the covered drums, the true PBZ 

CO concentrations would be hard to determine using the direct 

reading instruments. However, our air sampling results indicate that 

Discussion

 (continued)
Health Hazard Evaluation Report 2008-0045-3145 Page 13

a possible hazard from CO exposure might exist; this can be easily 

mitigated by keeping the drums uncovered to prevent the buildup 

of gases in the drums.

The company has installed a new horizontal belt vacuum filtration 

system that uses a paper filtration process. The new process 

generates wet silicon mud, which is stored in an open 55-gallon 

plastic storage drum. This process change has obviated the use of 

polypropylene filters, and open drum storage prevents the buildup 

of gases. Although we have not evaluated the new process, the 

company continues to use the colorimetric detector to monitor the 

drum for hydride gases.

Discussion

 (continued)

Recommendations

On the basis of a scientific literature review and air sampling 

results, we conclude that the covered drums were pressurized 

primarily because of H2

 formation and that silane was also formed. 

We could not confirm that the apparent high CO concentrations 

inside covered drums were accurate because of conflicting results 

obtained with different measurement and analytical methods. 

Regardless, disposing of used filters from the silicon wafer grinding 

filtration process in covered drums may pose a health and safety 

hazard to employees. This hazard can be minimized by leaving the 

drums uncovered, and/or by a process modification, as is now 

done by this company.

Conclusions

On the basis of our findings, we recommend the actions listed 

below to create a more healthful workplace. We encourage the 

company to use a labor-management health and safety committee 

or working group to discuss the recommendations in this report 

and develop an action plan. Those involved in the work can best 

set priorities and assess the feasibility of our recommendations for 

the specific situation at your workplace. Our recommendations are 

based on the hierarchy of controls approach (refer to Appendix B: 

Occupational Exposure Limits and Health Effects). This approach 

groups actions by their likely effectiveness in reducing or removing 

hazards. In most cases, the preferred approach is to eliminate 

hazardous materials or processes and install engineering controls 

to reduce exposure or shield employees. Until such controls are 

in place, or if they are not effective or feasible, administrative 

measures and/or PPE may be needed.
Page 14 Health Hazard Evaluation Report 2008-0045-3145

Recommendations

 (continued) Administrative Controls

Administrative controls are management-dictated work practices 

and policies to reduce or prevent exposures to workplace hazards. 

The effectiveness of administrative changes in work practices 

for controlling workplace hazards is dependent on management 

commitment and employee acceptance. Regular monitoring and 

reinforcement is necessary to ensure that control policies and 

procedures are not circumvented in the name of convenience or 

production.

1. Leave the drums uncovered to prevent the buildup of gases.

2. Post signs near the work area to remind employees not to 

cover the drums.

3. Instruct employees who experience symptoms like headache, 

nausea, or confusion to promptly report them to the on-site 

healthcare professional.

References

ACGIH [1989]. Hazard assessment and control technology 

in semiconductor manufacturing. American Conference 

of Governmental Industrial Hygienists. Chelsea, MI: Lewis 

Publishers, Inc., p. 97.

Biosystems [2011]. Reference manual: ToxiUltra single sensor gas 

detector. Biosystems: Middletown, CT, p. 55.

Burgess W [1995]. Recognition of health hazards in industry: a 

review of materials and processes. 2nd ed. New York: John Wiley 

and Sons, Inc.

Chemguide [2010]. Chemical reactions of the period 3 elements 

[http://www.chemguide.co.uk/inorganic/period3/elementsreact.

html]. Date accessed: October 2011.

Doremus RH, Breed DJ [1976]. Hydrogen profiles in water-oxidized 

silicon. J Phy Chem 80(22):2471–2473.

Gatech [2010]. Silicon dioxide [http://www.ece.gatech.edu/

research/labs/vc/theory/oxide.html]. Date accessed: October 2011.
Health Hazard Evaluation Report 2008-0045-3145 Page 15

Heckathorn H [2011]. Cross-interference for CO – GasAlertClip 

Extreme. Private e-mail message to Srinivas Durgam (sdurgam@

cdc.gov), March 15.

Lampert I, Fubstetter H, Jacob H [1986]. Evidence of SiH4

formation during the reaction of water with a silicon surface. J 

Electrochem Soc 133(7):1472–1474.

Salonen J, Lehto V-P, Laine E [1997]. The room temperature 

oxidation of porous silicon. App Surf Sci 120(3-4):191–198.

Stephen RG, Riley FL [1989]. Oxidation of silicon by water. J Eur 

Ceram Soc 5(4):219–222.

Walker L [2011]. Requested information from Dräger Safety. 

Private e-mail message to Srinivas Durgam (sdurgam@cdc.gov), 

March 14.

References

 (continued)
Page 16 Health Hazard Evaluation Report 2008-0045-3145

Appendix A: Methods

Carbon Monoxide, Carbon Dioxide, and Hydrogen in Air

NIOSH investigators measured CO air concentrations with ToxiUltra Atmospheric Monitors 

(Biosystems, Inc., Middletown, Connecticut), a BW Technologies GasAlert Extreme single gas detector 

(Honeywell Analytics, Calgary, Alberta), and a Dräger Pac III single gas monitor (Dräger Safety Inc., 

Pittsburgh, Pennsylvania). All these instruments were fitted with manufacturer recommended CO 

sensors. All the direct reading instruments were zeroed and calibrated before each use according to the 

manufacturer’s recommendations. These monitors are direct-reading instruments with data logging 

capabilities. The instruments were operated in the passive diffusion mode, with a 1-minute sampling 

interval. The ToxiUltra has a nominal range of 0 to 500 ppm with the highest instantaneous reading 

of 1,000 ppm, BW Technologies has a nominal range of 0 to 1,000 ppm, and Dräger Pac III has a 

nominal range of 0 to 10,000 ppm.

Vacutainer® (BD, Franklin Lakes, New Jersey) air samples were analyzed by two laboratories. Bureau 

Veritas North America, the NIOSH contract laboratory, analyzed a set of vacutainer air samples using 

GC-TCD/FID. A set of duplicate air samples was sent to the OSHA Salt Lake Technical Center where 

they were analyzed by GC-MS. The analytical LOD and LOQ for the three gases analyzed by GC-TCD/

FID are presented in Table A1.

Table A1. Analytical method LOD and LOQ for vacutainer air sample analysis

Site visit date

Analytical method

GC-TCD/FID

H2

(ppm)

CO

(ppm)

CO2

(ppm)

Feb 2008 LOD 5,000 100 1,000

LOQ 17,000 330 3,300

Mar 2009 LOD 10,000 100 1,000

LOQ 33,000 330 3,300

CO concentrations were also measured using Dräger Tubes®, colorimetric detection tubes, model 8/a 

(range of 8 to 150 ppm) (Dräger Safety Inc, Pittsburgh, Pennsylvania). Tube 8/a is suitable for measuring 

CO concentrations when H2 gas is also expected to be present. Accuro® pumps were used for drawing air 

through the colorimetric tubes.
Health Hazard Evaluation Report 2008-0045-3145 Page 17

Appendix B: Occupational Exposure Limits & Health Effects

In evaluating the hazards posed by workplace exposures, NIOSH investigators use both mandatory (legally 

enforceable) and recommended OELs for chemical, physical, and biological agents as a guide for making 

recommendations. OELs have been developed by federal agencies and safety and health organizations to 

prevent the occurrence of adverse health effects from workplace exposures. Generally, OELs suggest levels 

of exposure that most employees may be exposed to for up to 10 hours per day, 40 hours per week, for a 

working lifetime, without experiencing adverse health effects. However, not all employees will be protected 

from adverse health effects even if their exposures are maintained below these levels. A small percentage 

may experience adverse health effects because of individual susceptibility, a preexisting medical condition, 

and/or a hypersensitivity (allergy). In addition, some hazardous substances may act in combination with 

other workplace exposures, the general environment, or with medications or personal habits of the 

employee to produce adverse health effects even if the occupational exposures are controlled at the level set 

by the exposure limit. Also, some substances can be absorbed by direct contact with the skin and mucous 

membranes in addition to being inhaled, which contributes to the individual’s overall exposure.

Most OELs are expressed as a TWA exposure. A TWA refers to the average exposure during a normal 8- 

to 10-hour workday. Some chemical substances and physical agents have recommended STEL or ceiling 

values where adverse health effects are caused by exposures over a short period. Unless otherwise noted, 

the STEL is a 15-minute TWA exposure that should not be exceeded at any time during a workday, and 

the ceiling limit is an exposure that should not be exceeded at any time.

In the United States, OELs have been established by federal agencies, professional organizations, state 

and local governments, and other entities. Some OELs are legally enforceable limits, while others are 

recommendations. The U.S. Department of Labor OSHA PELs (29 CFR 1910 [general industry]; 29 

CFR 1926 [construction industry]; and 29 CFR 1917 [maritime industry]) are legal limits enforceable 

in workplaces covered under the Occupational Safety and Health Act of 1970. NIOSH RELs are 

recommendations based on a critical review of the scientific and technical information available on a 

given hazard and the adequacy of methods to identify and control the hazard. NIOSH RELs can be found 

in the NIOSH Pocket Guide to Chemical Hazards [NIOSH 2010]. NIOSH also recommends different 

types of risk management practices (e.g., engineering controls, safe work practices, employee education/

training, personal protective equipment, and exposure and medical monitoring) to minimize the risk of 

exposure and adverse health effects from these hazards. Other OELs that are commonly used and cited 

in the United States include the TLVs recommended by ACGIH, a professional organization, and the 

WEELs recommended by the American Industrial Hygiene Association, another professional organization. 

The TLVs and WEELs are developed by committee members of these associations from a review of the 

published, peer-reviewed literature. They are not consensus standards. ACGIH TLVs are considered 

voluntary exposure guidelines for use by industrial hygienists and others trained in this discipline “to assist 

in the control of health hazards” [ACGIH 2011]. WEELs have been established for some chemicals “when 

no other legal or authoritative limits exist” [AIHA 2011].

Outside the United States, OELs have been established by various agencies and organizations and 

include both legal and recommended limits. The Institut für Arbeitsschutz der Deutschen Gesetzlichen 

Unfallversicherung (IFA, Institute for Occupational Safety and Health of the German Social Accident 
Page 18 Health Hazard Evaluation Report 2008-0045-3145

Insurance) maintains a database of international OELs from European Union member states, Canada 

(Québec), Japan, Switzerland, and the United States. The database, available at http://www.dguv.de/ifa/

en/gestis/limit_values/index.jsp, contains international limits for over 1,500 hazardous substances and is 

updated periodically.

Employers should understand that not all hazardous chemicals have specific OSHA PELs, and for some 

agents the legally enforceable and recommended limits may not reflect current health-based information. 

However, an employer is still required by OSHA to protect its employees from hazards even in the absence 

of a specific OSHA PEL. OSHA requires an employer to furnish employees a place of employment free 

from recognized hazards that cause or are likely to cause death or serious physical harm [Occupational 

Safety and Health Act of 1970 (Public Law 91–596, sec. 5(a)(1))]. Thus, NIOSH investigators encourage 

employers to make use of other OELs when making risk assessments and risk management decisions to 

best protect the health of their employees. NIOSH investigators also encourage the use of the traditional 

hierarchy of controls approach to eliminate or minimize identified workplace hazards. This includes, in 

order of preference, the use of (1) substitution or elimination of the hazardous agent, (2) engineering 

controls (e.g., local exhaust ventilation, process enclosure, dilution ventilation), (3) administrative controls 

(e.g., limiting time of exposure, employee training, work practice changes, medical surveillance), and (4) 

personal protective equipment (e.g., respiratory protection, gloves, eye protection, hearing protection). 

Control banding, a qualitative risk assessment and risk management tool, is a complementary approach 

to protecting employee health that focuses resources on exposure controls by describing how a risk 

needs to be managed. Information on control banding is available at http://www.cdc.gov/niosh/topics/

ctrlbanding/. This approach can be applied in situations where OELs have not been established or can be 

used to supplement the OELs, when available.

Below we provide the OELs and surface contamination limits for the compounds we measured, as well as a 

discussion of the potential health effects from exposure to these compounds.

Carbon Monoxide

CO is a colorless, odorless, tasteless gas produced by incomplete burning of carbon-containing materials 

such as gasoline or propane fuel. The initial symptoms of CO poisoning may include headache, dizziness, 

drowsiness, or nausea. Symptoms may advance to vomiting, loss of consciousness, and collapse if 

prolonged or high exposures are encountered. If the exposure level is high, loss of consciousness may 

occur without other symptoms. Coma or death may occur if high exposures continue [NIOSH 1972, 1977, 

1979, 2010; Proctor et al. 1988; ACGIH 2011]. The display of symptoms varies widely from individual to 

individual, and may occur sooner in susceptible individuals such as young or aged people, people with 

preexisting lung or heart disease, or those living at high altitudes.

Exposure to CO limits the ability of the blood to carry oxygen to the tissues by binding with the 

hemoglobin to form carboxyhemoglobin. Once exposed, the body compensates for the reduced 

bloodborne oxygen by increasing cardiac output, thereby increasing blood flow to specific oxygenAppendix B: Occupational Exposure Limits & Health Effects

 (continued)
Health Hazard Evaluation Report 2008-0045-3145 Page 19

demanding organs such as the brain and heart. This ability may be limited by preexisting heart or lung 

diseases that inhibit increased cardiac output.

Occupational criteria for CO exposure are applicable to employees who may be at risk of CO poisoning. 

The NIOSH REL for CO is 35 ppm for full-shift TWA exposure, with a ceiling limit of 200 ppm that 

should never be exceeded [NIOSH 1992]. The NIOSH REL of 35 ppm is designed to protect workers 

from health effects associated with carboxyhemoglobin levels in excess of 5% [NIOSH 1972]. NIOSH 

has established the IDLH value for CO of 1200 ppm [NIOSH 2000]. An IDLH value is defined as a 

concentration at which an immediate or delayed threat to life exists or that would interfere with an 

individual’s ability to escape unaided from a space.

The ACGIH recommends an 8-hour TWA TLV of 25 ppm on the basis of limiting shifts in 

carboxyhemoglobin levels to less than 3.5%, thus minimizing adverse neurobehavioral changes such as 

headache, dizziness, etc., and to maintain cardiovascular exercise capacity [ACGIH 2011]. ACGIH also 

recommends that exposures never exceed five times the TLV (thus, never to exceed 125 ppm) [ACGIH 

2011]. The OSHA PEL for CO is 50 ppm for an 8-hour TWA exposure [29 CFR 1910.1000].

Carbon Dioxide

Carbon dioxide is a clear and odorless gas and is a simple asphyxiant [LaDou 2004]. It is a product of 

respiratory metabolism and is not considered a building air pollutant. The NIOSH REL and ACGIH TLV 

for CO2

 is 5,000 ppm as a full-shift TWA exposure and a STEL of 30,000 ppm [NIOSH 2010; ACGIH 

2011]. The OSHA PEL for CO2

 is 5,000 ppm for an 8-hour TWA exposure [29 CFR 1901.1000].

Hydrogen

Hydrogen gas is the lightest gas and is colorless, odorless, and tasteless. Hydrogen gas is highly combustible 

and will burn at concentrations ranging from 4% to 75% with the lower explosive limit being 4%. Because 

of its explosive nature it poses a safety hazard, and at high concentrations it can also act as a simple 

asphyxiant [LaDou 2004]. Requirements governing safe storage and delivery of hydrogen are covered under 

the OSHA standard 29 CFR 1910.103.

Silane

Silane or SiH4 is a colorless gas with a strong odor at room temperature that acts as a respiratory irritant. 

It is a pyrophoric gas, i.e., it spontaneously combusts in air. Concentrations greater than 3% silane in 

nitrogen or greater than 0.5% in hydrogen may ignite spontaneously in contact with ambient air [ACGIH 

1989]. When released from a cylinder silane may generate enough static electrical charge to initiate a 

flame. Silane is a very hazardous gas with high potential to cause damage to life and property.

Appendix B: Occupational Exposure Limits & Health Effects

 (continued)
Page 20 Health Hazard Evaluation Report 2008-0045-3145

The NIOSH REL for silane is 5 ppm as a full-shift TWA exposure [NIOSH 2010]. The ACGIH also 

recommends an 8-hour TWA TLV of 5 ppm and an excursion limit of 25 ppm [ACGIH 2011].

References

ACGIH [1989]. Hazard assessment and control technology in semiconductor manufacturing. American 

Conference of Governmental Industrial Hygienists. Chelsea, MI: Lewis Publishers, Inc., p. 98.

ACGIH [2011]. 2011 TLVs® and BEIs®: threshold limit values for chemical substances and physical 

agents and biological exposure indices. Cincinnati, OH: American Conference of Governmental 

Industrial Hygienists.

AIHA [2011]. AIHA 2011 Emergency response planning guidelines (ERPG) & workplace environmental 

exposure levels (WEEL) handbook. Fairfax, VA: American Industrial Hygiene Association.

CFR. Code of Federal Regulations. Washington, DC: U.S. Government Printing Office, Office of the 

Federal Register.

LaDou J, ed. [2004]. Current occupational and environmental medicine. 3rd ed. New York: The McGrawHill Companies, Inc., p. 540.

NIOSH [1972]. Criteria for a recommended standard: occupational exposure to carbon monoxide. 

Cincinnati, OH: U.S. Department of Health, Education, and Welfare, Health Services and Mental Health 

Administration, National Institute for Occupational Safety and Health, DHEW (NIOSH) Publication No. 

73-11000.

NIOSH [1977]. Occupational diseases: a guide to their recognition. Rev. ed. Cincinnati, OH: U.S. 

Department of Health, Education, and Welfare, Centers for Disease Control, National Institute for 

Occupational Safety and Health, DHEW (NIOSH) Publication No. 77-181.

NIOSH [1979]. A guide to work-relatedness of disease. Rev. ed. Cincinnati, OH: U.S. Department of 

Health, Education, and Welfare, Centers for Disease Control, National Institute for Occupational Safety 

and Health, DHEW (NIOSH) Publication No. 79-116.

NIOSH [1992]. Recommendations for occupational safety and health: compendium of policy documents 

and statements. By Dames BL. Cincinnati, OH: U.S. Department of Health and Human Services, Centers 

for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS 

(NIOSH) Publication No. 92-100.

Appendix B: Occupational Exposure Limits & Health Effects

 (continued)
Health Hazard Evaluation Report 2008-0045-3145 Page 21

NIOSH [2000]. Documentation for immediately dangerous to life or health concentrations. In: NIOSH 

pocket guide to chemical hazards and other databases. Cincinnati, OH: U.S. Department of Health and 

Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety 

and Health, DHHS (NIOSH) Publication No. 2000-130.

NIOSH [2010]. NIOSH pocket guide to chemical hazards. Cincinnati, OH: U.S. Department of Health 

and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational 

Safety and Health, DHHS (NIOSH) Publication No. 2010-168c. [http://www.cdc.gov/niosh/npg/]. Date 

accessed: October 2011.

Proctor NH, Hughes JP, Fischman ML [1988]. Chemical hazards of the workplace. Philadelphia, PA: J.B. 

Lippincott Company.

Appendix B: Occupational Exposure Limits & Health Effects

 (continued)
Page 22 Health Hazard Evaluation Report 2008-0045-3145

Appendix C: Tables

Table C1. Vacutainer air sampling results (February 7, 2008)

Location 

(Date filters were removed)

Time of sample 

collection 

(military)

Air concentration (ppm)

H2 CO CO2

Cartridge tank 1

09:33 64,500 22,400 17,000

09:37 32,300 8,600 5,600

Cartridge tank 2 09:49 (12,000)* 3,500 3,400

Drum (1/18/08)

10:14 26,200 7,500 5,900

10:15 ND 2,200 (2,900)*

Basement — ND ND ND

— ND ND ND

Office (Building 1, 2nd floor)

14:28 ND ND ND

14:28 ND ND ND

ND = Not detected; the concentration is below the LOD.

*Concentrations between LOD and LOQ are listed in the table in parentheses to acknowledge that there is 

more uncertainty surrounding concentrations below the LOQ.

Table C2. Drum vacutainer air sampling results (February 7, 2008)

Location

(Date filters were 

removed)

Time elapsed 

after covering 

the drum 

(hh:mm:ss)

Drum interior 

temperature 

(oF)

Air concentration (ppm)

H2 CO CO2

Drum (2/7/08)

0:06:00 74.9 ND 1,100 ND

0:11:00 74.1 53,800 19,900 16,700

0:21:00 74.0 (5,400)* ND ND

0:31:00 74.1 (14,000)* ND ND

0:31:30 74.1 (14,000)* ND ND

0:41:20 74.5 17,300 ND ND

1:01:30 74.6 27,100 ND ND

2:00:10 76.6 74,700 ND ND

2:01:18 76.6 32,300 8,500 9,600

2:48:45 77.3 48,900 2,000 (3,000)*

2:49:10 77.4 36,100 ND ND

3:46:30 77.8 ND ND ND

3:46:50 77.9 84,700 ND ND

ND = Not detected; the concentration is below the LOD.

*Concentrations between LOD and LOQ are listed in the table in parentheses to acknowledge that there is 

more uncertainty surrounding concentrations below the LOQ.
Health Hazard Evaluation Report 2008-0045-3145 Page 23

Table C3. Vacutainer air sampling results (March 18, 2009)

Location 

(Date filters were removed)

Time of sample 

collection

(military)

Air concentration (ppm)

H2 CO CO2

Bag filter tank 1C 07:17 ND 15,600 8,930

Cartridge tank 1A 07:38 ND 3,140 (1,240)*

Cartridge tank 1B 07:53 ND 15,800 ND

Bag filter tank 1A 08:09 ND 3,270 (2,070)*

Bag filter tank 1B 08:16 ND (303)* ND

Drum (3/12/09)

09:32 (32,100)* 19,400 15,000

09:33 (27,900)* 11,000 6,790

09:33 34,000 5,280 3,750

Basement

15:03 46,400 1,410 (1,700)*

15:03 ND (128)* ND

ND = Not detected; the concentration is below the LOD.

*Concentrations between LOD and LOQ are listed in the table in parentheses to acknowledge that there is 

more uncertainty surrounding concentrations below the LOQ.

Table C4. Drum vacutainer air sampling results (March 18, 2009)

Location

(Date filters were 

removed)

Time elapsed after 

covering the drum 

(hh:mm)

Drum interior 

temperature 

(oF)

Air concentration (ppm)

H2 CO CO2

Drum (3/18/09)

0:12 66.7 (13,800)* 1,880 (2,310)*

0:17 66.7 ND 792 (1,040)*

0:27 66.9 (10,700)* (229)* ND

0:49 68.0 (17,700)* ND ND

0:59 68.5 (10,900)* 7,650 6,860

1:32 70.6 (25,900)* 2,610 ND

1:32 70.7 34,400 1,320 (1,740)*

2:13 73.5 39,400 (192)* (1,070)*

2:46 75.6 58,500 ND ND

3:16 77.3 70,700 ND ND

3:16 77.3 79,600 ND ND

3:47 78.8 54,100 21,600 18,800

4:20 79.9 88,200 10,900 9,710

4:20 79.9 103,000 5,670 4,310

5:00 81.2 118,000 2,030 7,890

ND = Not detected; the concentration is below the LOD.

*Concentrations between LOD and LOQ are listed in the table in parentheses to acknowledge that there is 

more uncertainty surrounding concentrations below the LOQ.

Appendix C: Tables

 (continued)
Page 24 Health Hazard Evaluation Report 2008-0045-3145

Appendix C: Tables

 (continued)

Table C5. Vacutainer air sampling results (March 19, 2009)

Location 

(Date filters were removed)

Time of sample collection

(military)

Air concentration (ppm)

H2 CO CO2

Drum (3/12/09)

07:44 (15,500)* ND ND

07:44 (13,900)* 21,400 18,600

07:44 (24,400)* 6,780 4,900

07:44 (25,400)* 4,620 3,430

Drum (3/18/09)

07:46 138,000 2,900 (3,120)*

07:46 150,000 1,050 ND

07:46 153,000 643 ND

ND = Not detected; the concentration is below the LOD.

*Concentrations between LOD and LOQ are listed in the table in parentheses to acknowledge that there is 

more uncertainty surrounding concentrations below the LOQ.

Table C6. PBZ air sampling results (March 18–19, 2009)

Date Job title Instrument

Sampling 

time 

(minutes)

Air concentration (ppm)

Mean (Min–Max)

H2 CO CO2

3/18 Maintenance technician

Toxi Ultra 380 — 1.94 (0–27.3) —

BW 380 — 4.50 (0–29.0) —

Pac-III 380 — 0.078 (0–25.0) —

3/19 Industrial hygienist

Toxi Ultra 18 — 8.70 (2.1–230) —

BW 18 — 34.2 (3–140) —

Pac-III 18 — 19.0 (0–375) —

3/19

Industrial hygienist opening 

drum containing filters 

removed on 3/12/09

Vacutainer Grab 57,800 (228)* ND

3/19

Industrial hygienist opening 

drum containing filters 

removed on 3/18/09

Vacutainer Grab (29,800)* ND ND

NIOSH Ceiling/STEL 200 30,000

ACGIH STEL 125† 30,000

ND = Not detected; the concentration is below the LOD.

*Concentrations between LOD and LOQ are listed in the table in parentheses to acknowledge that there is 

more uncertainty surrounding concentrations below the LOQ.

† ACGIH excursion limit = 5 x ACGIH TLV of 25 ppm
Health Hazard Evaluation Report 2008-0045-3145 Page 25

Acknowledgments and

Availability of Report The Hazard Evaluations and Technical Assistance Branch (HETAB) 

of the National Institute for Occupational Safety and Health 

(NIOSH) conducts field investigations of possible health hazards 

in the workplace. These investigations are conducted under the 

authority of Section 20(a)(6) of the Occupational Safety and Health 

Act of 1970, 29 U.S.C. 669(a)(6) which authorizes the Secretary of 

Health and Human Services, following a written request from any 

employer or authorized representative of employees, to determine 

whether any substance normally found in the place of employment 

has potentially toxic effects in such concentrations as used or found. 

HETAB also provides, upon request, technical and consultative 

assistance to federal, state, and local agencies; labor; industry; and 

other groups or individuals to control occupational health hazards 

and to prevent related trauma and disease.

Mention of any company or product does not constitute 

endorsement by NIOSH. In addition, citations to websites 

external to NIOSH do not constitute NIOSH endorsement of 

the sponsoring organizations or their programs or products. 

Furthermore, NIOSH is not responsible for the content of these 

websites. All Web addresses referenced in this document were 

accessible as of the publication date.

This report was prepared by Srinivas Durgam of HETAB, Division 

of Surveillance, Hazard Evaluations and Field Studies and Robert 

Streicher of Chemical Exposure and Monitoring Branch, Division 

of Applied Research and Technology. Industrial hygiene field 

assistance was provided by Seung-Hee Jang, Chad Dowell, and 

Kenneth Fent. Industrial hygiene equipment and logistical support 

was provided by Donald Booher and Karl Feldmann. Analytical 

support was provided by Bureau Veritas North America and the 

Occupational Safety and Health Administration Salt Lake City 

Technical Center. Health communication assistance was provided 

by Stefanie Evans. Editorial assistance was provided by Ellen 

Galloway. Desktop publishing was performed by Greg Hartle.

Copies of this report have been sent to employee and management 

representatives at the company, the state health department, 

and the Occupational Safety and Health Administration 

Regional Office. This report is not copyrighted and may be freely 

reproduced. The report may be viewed and printed at http://

www.cdc.gov/niosh/hhe/. Copies may be purchased from the 

National Technical Information Service at 5825 Port Royal Road, 

Springfield, Virginia 22161.
Below is a recommended citation for this report:

NIOSH [2011]. Health hazard evaluation report: unknown gases generated from 

a silicon wafer grinding filtration process – Colorado. By Durgam S, Streicher 

R. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for 

Disease Control and Prevention, National Institute for Occupational Safety and 

Health, NIOSH HETA No. 2008-0045-3145.

To receive NIOSH documents or information about 

occupational safety and health topics, contact NIOSH at:

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For a monthly update on news at NIOSH, subscribe to 

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