Evaluation of Occupational 

Exposures and Indoor 

Environmental Quality in an 

Underground Cavern Workplace 

HHE Report No. 2018-0181-3389

August 2023 
Authors: Scott E. Brueck, MS, CIH, COHC

Duane R. Hammond, MS, PE 

Leonard M. Zwack, ScD, CIH

Sarah Hatcher, PhD

Analytical Support: Jennifer Roberts, Bureau Veritas North America

Desktop Publisher: Shawna Watts

Editor: Cheryl Hamilton

Logistics: Donnie Booher, Kevin Moore 

Keywords: North American Industry Classification System (NAICS) 712110 (Museums), Wood 

dust, Noise, Carbon monoxide, Indoor environmental quality, IEQ, Radon, Particles, Illumination, 

Cave cotton, Epsomite, Cavern, Artwork, Ohio. 

Disclaimer

The Health Hazard Evaluation Program investigates possible health hazards in the workplace under

the authority of the Occupational Safety and Health Act of 1970 [29 USC 669a(6)]. The Health

Hazard Evaluation Program also provides, upon request, technical assistance to federal, state, and

local agencies to investigate occupational health hazards and to prevent occupational disease or

injury. Regulations guiding the Program can be found in Title 42, Code of Federal Regulations,

Part 85; Requests for Health Hazard Evaluations [42 CFR Part 85]. 

Availability of Report

Copies of this report have been sent to the employer and employees. The state and local health

department and the Occupational Safety and Health Administration Regional Office have also

received a copy. This report is not copyrighted and may be freely reproduced.

Recommended Citation

NIOSH [2023]. Evaluation of occupational exposures and indoor environmental quality in an

underground cavern workplace. By Brueck SE, Hammond DR, Zwack LM, Hatcher S. Cincinnati,

OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention,

National Institute for Occupational Safety and Health, Health Hazard Evaluation Report

2018-0181-3389, https://www.cdc.gov/niosh/hhe/reports/pdfs/2018-0181-3389.pdf. 
Table of Contents

Main Report

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

Our Approach ................................................................................................................................................... 1

Our Key Findings.............................................................................................................................................. 2

Our Recommendations.................................................................................................................................... 3

Supporting Technical Information 

Section A: Workplace Information............................................................................................................ A-1

Section B: Methods, Results, and Discussion .......................................................................................... B-1

Methods: Exposure Assessment ............................................................................................................ B-1

Results and Discussion: Exposure Assessment ................................................................................... B-2

Methods: Ventilation and Air Exchange............................................................................................... B-8

Results and Discussion: Ventilation and Air Exchange...................................................................... B-9

Methods: Evaluation of “Cave Cotton” Mineral Fibers and Oil-like Residue Collected from 

Cavern Walls........................................................................................................................................... B-10

Results and Discussion: Evaluation of “Cave Cotton” Mineral Fibers and Oil-like Residue 

Collected from Cavern Walls................................................................................................................ B-10

Methods: Illumination Levels............................................................................................................... B-13

Results and Discussion: Illumination Levels...................................................................................... B-13

Methods: Employee Health Assessment ............................................................................................ B-13

Results and Discussion: Employee Health Assessment ................................................................... B-13

Limitations............................................................................................................................................... B-14

Conclusions............................................................................................................................................. B-15

Section C: Tables.......................................................................................................................................... C-1

Section D: Occupational Exposure Limits............................................................................................... D-1

Carbon Monoxide ................................................................................................................................... D-2

Wood Dust............................................................................................................................................... D-2

Noise ......................................................................................................................................................... D-3

Radon ........................................................................................................................................................ D-5

Section E: References.................................................................................................................................. E-1

Methods..................................................................................................................................................... E-1

Occupational Exposure Limits............................................................................................................... E-1

Results and Discussion............................................................................................................................ E-3
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1

Introduction

Request

An employer representative of a warehouse facility, located in a former underground limestone quarry, 

requested a health hazard evaluation concerning employees’ exposures to carbon monoxide, wood dust

and other airborne particles, noise, and radon. The employer also wanted to know what the fibrous 

material and oil-like residue were on some of the cavern walls of the warehouse workspace. 

Workplace

Five employees were working at the facility during the site visits. The warehouse was housed in a leased 

33-thousand-square-foot space located within a large 4-million-square-foot underground cavern. The 

large cavern was a former limestone quarry 75 to 100 feet below ground. Vehicles used a paved 

concrete road to drive to the multiple other businesses in the cavern. 

The company had a 1,200-square-foot woodshop within the warehouse space, partially separated from 

the warehouse area by a half-wall partition. Among other items, the woodshop held a table saw, miter 

saw, router, and handheld power tools. A small painting area outside the woodshop was used for 

limited painting. 

To learn more about the workplace, go to Section A in the Supporting Technical Information

Our Approach

We visited the workplace on two occasions to learn more about exposures and health concerns. During 

our first visit on October 11, 2018, we did the following: 

• Observed work processes, practices, and workplace conditions, and spoke with employees. 

• Measured carbon monoxide, carbon dioxide, temperature, and relative humidity throughout the 

workplace, in the cavern directly outside the workplace, and outdoors. 

• Took sound level measurements while workers used powered woodworking equipment and 

tools in the woodshop. 

On our second visit, December 11, 2018, we completed these tasks:

• Collected full-shift personal air samples for wood dust and noise on employees doing 

woodworking and painting tasks.

• Collected area air samples for wood dust, noise, and other airborne particles.

• Set up two instruments to continuously measure carbon monoxide, carbon dioxide, relative 

humidity, temperature, and radon for 10 days.

• Used tracer gas to measure the air exchange rate in the cavern workspace.
2

• Collected bulk samples of fibrous material (referred to as “cave cotton”) and an oil-like residue

found on some of the rock walls of the cavern.

• Measured illumination levels at various locations throughout the space.

• Interviewed five employees on topics such as job tenure, job tasks, perceived noise exposure, 

personal protective equipment use, relevant medical history, and health symptoms and concerns.

To learn more about our methods, go to Section B in the Supporting Technical Information

Our Key Findings

Carbon monoxide and radon levels were well below occupational exposure limits 

• Employees were not overexposed to carbon monoxide. Although carbon monoxide levels could 

be higher sometimes, depending on the amount of vehicle traffic and vehicle exhaust in the 

main cavern passageway. 

• Radon levels in the cavern workspace were well below the Occupational Safety and Health 

Administration (OSHA) permissible exposure limit for workplaces. 

• Radon levels were above recommended levels set by the Environmental Protection Agency 

(EPA). But the EPA limits were established for a lifetime of exposure in homes instead of 

workplaces. 

Employee wood dust exposure in the woodshop could potentially be above

recommended occupational exposure limits, depending on how much time wood

working equipment is used

• Employees were mostly exposed to dust from pine wood. Exposures to wood dust for the 

8-hour shift was less than the National Institute of Occupational Safety and Health (NIOSH) 

recommended exposure limit. However, wood dust levels were at NIOSH limit during the 

6 hours that wood working equipment was in use. 

• Wood dust exposures in the painting area and at the employee work area outside the woodshop 

were well below occupational exposure limits.

Employee noise exposure in the woodshop was above the NIOSH recommended 

exposure limit, but lower than the OSHA action level and permissible exposure limit

• Employee noise exposure was above the NIOSH recommended exposure limit due to high 

sound levels from powered woodworking equipment. These sound levels were sometimes above 

95 decibels, A-weighted, occasionally reaching 100 decibels, A-weighted. 

• Noise exposure levels in the painting area and in the employee work area outside the woodshop 

were below NIOSH and OSHA noise exposure limits. 
3

• Employees sometimes used electronic noise canceling earmuffs or headphones when using 

woodworking equipment; however, these devices were not adequate for use as hearing 

protection.

Air exchange rates in the cavern warehouse were very low

• The warehouse did not have a mechanical ventilation system to bring outdoor air into 

workspace. Air exchange between the warehouse and the main cavern passageway occurred

when the large overhead door or loading dock door were open or through gaps around these 

doors when they were closed. However, air from main cavern passageway has the potential to be 

contaminated with exhaust from vehicles driven throughout the cavern. 

• Air exchange was very low. The air only changed about once every 13 hours between the cavern 

warehouse space and the main cavern passageway. 

To learn more about our results, go to Section B in the Supporting Technical Information

Our Recommendations

The Occupational Safety and Health Act requires employers to provide a safe workplace.

Benefits of Improving Workplace Health and Safety:

 Improved worker health and well-being  Improved image and reputation 

 Better workplace morale  Better products, processes, and services

 Better employee recruiting and retention  Increased overall cost savings

The recommendations below are based on the findings of our evaluation. For each recommendation, 

we list a series of actions you can take to address the issue at your workplace. The actions at the 

beginning of each list are preferable to the ones listed later. The list order is based on a well-accepted 

approach called the “hierarchy of controls.” The hierarchy of controls 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 personal protective equipment might be needed. Read more about the hierarchy of 

controls at https://www.cdc.gov/niosh/topics/hierarchy/. 

We encourage the company to use a health and safety committee to discuss our 

recommendations and develop an action plan. Both employee representatives and 

management representatives should be included on the committee. Helpful guidance can 

be found in Recommended Practices for Safety and Health Programs at 

https://www.osha.gov/shpguidelines/index.html.
4

Recommendation 1: Reduce wood dust exposures in the woodshop

Why? Exposure to airborne wood dust can cause health symptoms such as skin irritation, eye 

irritation, nasal irritation, throat irritation, coughing, and shortness of breath. Some hardwoods such 

as oak, maple, walnut, and western red cedar have been linked to nasal cancer. 

Air monitoring results showed that wood dust exposures could exceed recommended occupational 

exposure limits depending on how much time woodworking equipment is used.

How? At your workplace, we recommend these specific actions:

Improve wood dust capture at the table saw. 

• Install an exhaust hood over the top of the saw blade to better contain and exhaust the 

wood dust as it is thrown from the blade. The manufacturer of the table saw in the 

woodshop has an overarm dust collector available for use with that table saw.

• Rotate the table saw 90 degrees to allow the saw to be connected to the dust collector 

with a straight length of exhaust duct. This will reduce the total length of duct needed 

and eliminate a greater than 90-degree bend at its point of attachment to the table.

• Replace the corrugated plastic duct with rigid smooth interior duct. 

Improve wood dust capture at the compound miter saw. 

• Ensure that the dust extractor suction power settings are adjusted to fully capture dust 

at the saw.

• Replace the lengthy plastic exhaust hose connecting the miter saw and extractor with a 

shorter length of exhaust hose.

Recommendation 2: Reduce hearing loss risk from occupational noise exposure

Why? Noise-induced hearing loss is an irreversible condition that gets worse with noise exposure. 

Unlike some other types of hearing disorders, noise-induced hearing loss cannot be treated medically. 

Noise-exposed workers can develop substantial noise-induced hearing loss before it is clearly 

recognized.

Noise monitoring results showed that noise exposures in woodshop were above the NIOSH 

recommended noise exposure limits.
5

How? At your workplace, we recommend these specific actions:

Include woodshop employees in a hearing loss prevention program. 

• Provide baseline and annual audiometric testing and keep the hearing test results. 

• Evaluate audiograms using the NIOSH criteria for identifying standard threshold shifts, 

which are significant changes from baseline hearing audiograms. The NIOSH criteria 

are more protective than OSHA criteria and will provide earlier identification of 

employees with hearing loss.

• Educate employees on noise exposures and hearing loss risks. Give them information 

related to hearing hazards and hearing protection requirements. Explain to them which 

locations and job tasks require using hearing protection. 

• Instruct employees to promptly report any symptoms possibly related to workplace 

noise exposure, such as trouble hearing clearly, or ringing or buzzing in the ears. Keep

track of such reports. Encourage employees with possible work-related hearing 

concerns to seek medical care from qualified healthcare professionals. Include these 

reports in safety committee meetings.

• Require employees use appropriate hearing protection when they run powered 

woodworking equipment.

Recommendation 3: Supply outdoor air to the cavern warehouse

Why? This will help meet minimum ventilation standards for occupied buildings and reduce 

contaminants in the warehouse and woodshop areas. 

Although employees were not overexposed to carbon monoxide, the air exchange rate was very low. 

This could lead to a buildup of pollutants in the warehouse from the vehicles driven in the area.

How? At your workplace, we recommend these specific actions:

Supply outdoor air to the cavern warehouse space.

• Supply outdoor air to the warehouse by following ANSI/ASHRAE Standard 62.1-2022 

Ventilation and Acceptable Indoor Air Quality specifications for ventilation rates. 

• Ensure that outdoor air intakes are located at least 25 feet away from the closest place 

that vehicle exhaust is likely to be located (according to Table 5.5.1 of ANSI/ASHRAE 

Standard 62.1). This will prevent vehicle exhaust from being pulled into the cavern

warehouse space. 
6

Recommendation 4: Address other health and safety issues we identified during 

our evaluation

Why? A workplace can have multiple health hazards that cause worker illness or injury. These hazards 

can potentially cause health problems, lower morale and quality of life for your employees, and costs 

to your business. We saw the following potential issues at your workplace and recommend they be 

addressed: 

• Lighting in the painting area and in the area with employee workstations and conference table 

were below OSHA limits. 

• Employees reported concerns about lack of running water and bathrooms within the 

warehouse workspace. 

• Employees reported work-related health concerns and symptoms.

How? At your workplace, we recommend these specific actions:

Improve visibility by increasing lighting in the painting area and in the 

work area with employee workstations and conference table. 

• Improve lighting the painting area to 110 lux (lux is a unit of illumination or lighting). 

• Improve lighting in areas used for office related functions, such as the employee 

computer workstations and conference table, to 320 lux.

Add a portable toilet, handwashing station, self-contained emergency 

eyewash, and drinking water within the work area.

Encourage employees with health concerns to seek an evaluation from a 

healthcare provider who is familiar with occupational medicine and these 

types of exposures. 

• Resources for locating occupational medicine physicians include the Association of 

Occupational and Environmental Clinics (http://www.aoec.org) and the American 

College of Occupational and Environmental Medicine (http://www.acoem.org).
Supporting Technical Information

Evaluation of Occupational Exposures and 

Indoor Environmental Quality in an 

Underground Cavern Workplace

HHE Report No. 2018-0181-3389

August 2023
A-1

Section A: Workplace Information

The company leased a 33 thousand ft2 (square feet) warehouse space with 18–22 feet (ft) ceilings. The 

leased space was located within a large 4 million ft2 underground cavern that was a former limestone 

quarry 75–100 ft below ground. The underground cavern also housed multiple separate businesses. 

Vehicles traveled to and from the individual businesses on a paved concrete road. There was also

limited parking near the businesses inside the cavern. Most of the company’s leased space was used to 

store painted and sculptural artwork on large metal storage shelves. A small portion of the space was 

used as an open administrative office and included a conference table, worktables, and computer

workstations. A 1,200 ft2 woodshop was separated from the warehouse area by a half-wall partition. The 

woodshop was used for building shipping and storage containers for art pieces. It contained storage 

shelves, cabinets, worktables, and handheld power tools (table saw, miter saw, and router). A small 

painting area outside the woodshop was used for limited painting.

Five employees were working in the warehouse at the time of our visits. The median job tenure for 

these employees was 9 months (range: 6 months–4 years, 8 months). Their median age was 32 years 

(range: 28–43 years). Employees worked 8 hours per day, Monday through Friday. Most work was done 

in the warehouse space, but employees sometimes worked offsite when installing art at outside exhibits.
B-1

Section B: Methods, Results, and Discussion

The objectives of this evaluation included the following: 

• Assessing indoor environmental quality (IEQ) parameters; specifically, carbon monoxide (CO), 

carbon dioxide (CO2), relative humidity (RH), and temperature.

• Measuring wood dust, airborne particles, noise, and radon. 

• Evaluating ventilation and air exchange rates using tracer gas. 

• Analyzing samples of “cave cotton” and an oil-like residue from the cavern walls to determine 

their composition. 

• Measuring illumination levels. 

• Interviewing employees privately to discuss work-related health concerns and work-related 

health symptoms. 

Methods: Exposure Assessment 

Carbon Monoxide, Carbon Dioxide, Relative Humidity, Temperature 

During the initial site visit, we took spot measurements for CO, CO2, RH, and temperature in the 

workplace and outside the workplace (for comparison) using a TSI VelociCalc® Plus direct reading 

instrument. 

We also measured and data logged CO, CO2, RH, and temperature in the workplace using the TSI 

VelociCalc Plus for 10 days, during December 11–21. For these measurements, the sampling probe of 

the instrument was attached to the tripod at a height of about 5 ft to approximate worker breathing 

zone height. The instrument and tripod were placed near a wall in the main work area so that it did not 

interfere with employees’ work activities. The VelociCalc data logged an averaged measurement every 

15 minutes. Instrument data were downloaded, exported, and analyzed using Microsoft Excel for Office 

365 (Excel). 

Wood Dust 

We measured time-weighted average (TWA) personal wood dust exposures in the breathing zone of 

two employees. One employee worked primarily in the woodshop, and the other employee worked 

primarily in the nearby painting area. We also collected an area sample for wood dust at the employees’ 

workstation outside the woodshop. Wood dust samples were collected on pre-weighed 37-millimeter 

diameter polyvinyl chloride filters with Accucap inserts. The sample media was connected to air 

sampling pumps (SKC AirCheck Touch Model 220-5000TC) that were calibrated to a flow rate of 

2.0 liters per minute. Samples were analyzed using NIOSH Method 0600 [NIOSH 2023]. 

Airborne Particles 

We measured airborne particles in the air using a TSI DustTrakTM DRX 8533 aerosol monitor. The 

instrument was placed on a table in the main work area and continuously monitored and data logged an 

average measurement every 5 minutes during a monitoring period of 380 minutes. The DustTrak 
B-2

measured particles in 5 size ranges: PM1: ≤ 1.0 micron (μm); PM2.5: ≤ 2.5 μm; Respirable: ≤ 4 μm; 

PM10: ≤ 10 μm; and Total: > 10 μm. Instrument data were downloaded, exported, and analyzed using 

Excel. 

Noise 

We measured TWA personal noise exposures of two employees. One employee worked primarily in the 

woodshop, and the other worked primarily in the nearby painting area. We also collected an area sample 

for noise at the employees’ workstation outside the woodshop. We used Larson Davis SparkTM model 

706RC integrating noise dosimeters equipped with 0.335-inch random incidence microphones. The 

dosimeters recorded and data logged five-second averaged noise levels for the duration of the 

measurement period. The dosimeters were calibrated before and after the measurement periods 

according to the manufacturer’s instructions. 

We attached the dosimeter microphone to the outside the employee’s clothing in an upright position 

midway between the neck and the edge of their shoulder. The microphone was covered with a 

windscreen to reduce artifact noise caused by air movement or by accidental bumping or rubbing. The 

dosimeters simultaneously collected noise data using three different settings to allow comparison of 

noise measurement results with three different noise exposure limits: the NIOSH recommended 

exposure limit (REL), the OSHA permissible exposure limit (PEL), and the OSHA action level (AL). 

At the end of the work shift, we downloaded the noise measurement data from the dosimeters using 

PCB Piezotronics BlazeTM software.

We used a Larson Davis Model 831 type 1 integrating sound level meter and frequency analyzer 

equipped with a 0.5-inch random incidence microphone for sound level measurements. The sound level 

meter was calibrated before and after each day of measurements. The instrument integrated sound 

levels using linear averaging at 1-second time history intervals. During measurements, the sound level 

meter was handheld at a height of about 5 ft above floor or ground level. Most measurements were 

taken within 3–6 ft of employees for about 30–60 seconds. Following measurements, the noise 

measurement data stored on the instrument were downloaded, exported, and analyzed using Larson 

Davis G4® software and Excel.

Radon 

We measured radon levels using a Durridge RAD7 real-time continuous radon monitor for 10 days, 

during December 11–21. The intake probe of the instrument was attached to the tripod at a height of 

about 5 ft to approximate worker breathing zone height. The RAD7 and tripod were placed near a wall 

in the main work area so that it did not interfere with employees’ daily activities. The RAD7 recorded 

and data logged a measurement every 2 hours during this period. Instrument data were downloaded, 

exported, and analyzed using Excel.

Results and Discussion: Exposure Assessment

Carbon Monoxide, Carbon Dioxide, Relative Humidity, and Temperature

Results of short duration spot measurements across the warehouse during the initial walkthrough are 

shown in Table C1. In summary, CO levels ranged 1.8–2.1 parts per million (ppm), CO2 ranged 

1,218–1,237 ppm, RH ranged 53.2%–57.2%, and temperature ranged 68.8°F–70.7°F. These levels in the 
B-3

cavern outside the warehouse were CO (0 ppm), CO2 (560 ppm), RH (78.2%), and temperature 

(65.3°F). Outdoor levels outside the cavern were CO (0 ppm), CO2 (414 ppm), RH (38.9%), and 

temperature (68.0°F).

Table C2 provides the average and range for long-term continuous measurements. CO levels in the 

warehouse during this time averaged 0.1 ppm (range: 0–0.8 ppm). CO2 levels averaged 770 ppm (range: 

657–933). Both CO and CO2 levels were less than those measured during the October 11 initial visit. 

The reasons for this difference are unclear but could be potentially related to differences in air exchange 

or air movement between the two sampling periods. The amount of vehicle traffic through the cavern is 

another factor that could potentially influence CO levels. 

Long-term continuous measurements over 10 days showed that temperature and RH levels were similar 

to those measured during the initial visit. Temperature measurements taken inside the warehouse were 

within ANSI/ASHRAE recommendations. ANSI/ASHRAE Standard 55-2020, Thermal 

Environmental Conditions for Human Occupancy, specifies conditions in which 80% or more of the 

occupants would be expected to find the environment thermally acceptable [ANSI/ASHRAE 2020]. 

Assuming slow air movement and 50% RH, the operative temperatures recommended by 

ANSI/ASHRAE range from 68.5°F to 76°F in the winter and from 75°F to 80.5°F in the summer. The 

difference between the two is largely due to differences in seasonal clothing selection.

Similarly, humidity measurements taken in the warehouse were within ANSI/ASHRAE 

recommendations. ASHRAE Standard 62.1-2022, Ventilation for Acceptable Indoor Air Quality, 

recommends RH levels be limited to 65% or less for mechanical systems with dehumidification 

capability [ANSI/ASHRAE 2022]. The EPA recommends that RH be maintained below 60% (ideally 

30%‒50%) to prevent mold growth. Excessive humidity can also promote the growth of 

microorganisms and dust mites. The ASHRAE standard does not specify a lower humidity limit, but 

very low RH levels may contribute to dry and irritated mucous membranes of the eyes and airways 

[Wolkoff and Kjaergaard 2007].

Wood Dust 

TWA airborne wood dust measurement results are shown in Table C3. Before beginning work in the 

woodshop and painting areas, employees did administrative tasks in which they did not have wood dust 

exposures; therefore, we collected air samples for wood dust for under 6 hours of the 8-hour workday. 

Personal exposure measurement results during the monitoring period showed that the TWA wood dust 

exposure in the woodshop were at the NIOSH REL and American Conference of Governmental 

Industrial Hygienists (ACGIH®) threshold limit value (TLV®), both of which are 1 milligram per cubic 

meter (mg/m3) of air [ACGIH 2023; NIOSH 2010]. This suggests the potential for wood dust 

exposures to exceed these recommended occupational exposure limits (OELs) depending on the 

amount of time woodworking equipment is in use. Additional wood dust monitoring would help clarify 

day-to-day exposure variability. If we assumed no exposure for the unsampled portion of the work 

shift, full-shift personal wood dust exposure in the woodshop was 0.73 mg/m3. Employees reported 

sometimes using N95 respirators on a voluntary basis, depending on the amount of woodworking they 

were doing. Personal wood dust exposures in the painting area outside the woodshop and for the area 

sample collected at the workstation outside the woodshop were well below the NIOSH and ACGIH 
B-4

OELs. None of the wood dust exposures were at or above the OSHA PEL of 15 (mg/m3). When 

exposures exceed NIOSH or ACGIH recommended OELs, proper respiratory protection, along with a 

comprehensive respiratory protection program, is recommended.

On the day of air monitoring, the employee in the painting area did a limited amount of sanding using a 

handheld sander. The employee in the woodshop used the table saw, compound miter saw, and 

handheld router to cut and prepare various sized boards for building crates and other wood items. The 

wood was primarily pine. The table saw was connected to a Powermatic company dust collection 

system (Figure B1). The miter saw was connected to a mobile dust extractor built by the miter saw 

manufacturer, Festool (Figure B2). Because the router was also manufactured by Festool, this mobile 

dust extractor was disconnected from the miter saw and also used for the router. The company planned 

to purchase a separate mobile dust extractor for the handheld router.

Figure B1. Woodshop table saw with exhaust duct connected to the dust collector. Photo by NIOSH.

Figure B2. Compound miter saw connected to a mobile dust extractor. Photo by NIOSH.
B-5

Although the handheld router, miter, and table saw were connected to dust collection systems, 

improving dust capture efficiency of these dust collectors could increase their effectiveness and reduce 

wood dust exposures. The dust extractor suction power settings should be adjusted to adequately 

capture dust at the saw. Because the miter saw was permanently affixed to the worktable, replacing the 

lengthy plastic exhaust hose connecting the miter saw and extractor with a shorter length of exhaust 

hose could reduce air resistance within the hose and increase exhaust efficiency.

Wood dust at the table saw was exhausted through the bottom of the table and connected to the dust 

collector with large diameter corrugated plastic exhaust duct. Rotating the table saw 90° would allow the 

saw to be connected to the dust collector with a straight length of exhaust duct. This could improve 

capture efficiency by reducing the total length of duct needed and eliminate a greater than 90° bend at 

its point of attachment to the table. Replacing the corrugated duct with rigid smooth interior duct could 

also improve efficiency. In addition, installing an exhaust hood over the top of the saw blade can help 

contain and exhaust dust as it is thrown from the blade. Previous NIOSH laboratory testing has 

indicated that an exhaust hood can reduce wood dust emissions by 90% when it is installed on a typical 

table saw [NIOSH 1996]. The manufacturer of the table saw used in the woodshop has an overarm dust 

collector available for use with the saw.

Airborne Particles 

Table C4 provides a summary of minimum, maximum, and average particle concentrations measured in 

the main work area during the workday on the second visit. For all size ranges, the particle 

concentrations were far below the OSHA PEL for particulates not otherwise regulated of 5 mg/m3

(respirable fraction) and 15 mg/m3 (total dust) and the ACGIH TLV of 3 mg/m3 (respirable particles) 

and 10 mg/m3 (inhalable particles). Particle concentrations increased with particle size. However, the 

differences between PM1, PM2.5, and respirable-sized particles were minimal. Figure B3 shows how 

particle concentrations varied during the workday. Higher levels at times during the afternoon 

corresponded with woodworking activities and painting activities in adjacent work areas.
B-6

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Particulate Concentration (mg/m3)

Time

Total

PM10

Respirable

PM2.5

PM1

Figure B3. Time-history graph showing particle concentrations in the main work area on our second visit on

December 11. 

Noise 

Table C5 shows direct reading sound level measurement results. Overall, sound level measurements in 

the woodshop during use of woodworking equipment (table saw, miter saw, and router) ranged from 

approximately 86–94 decibels, A-weighted (dBA). Sound levels were highest during use of the handheld 

router, ranging 92–94 dBA. Background sound levels in the woodshop were 65–66 dBA when no 

woodworking equipment was in use. Sound levels in the painting area were about 76–78 dBA when the 

router was in use in the woodshop. Sound levels near the conference table outside the woodshop 

ranged from 62 dBA when no woodworking equipment was in use to 71 dBA when the table saw was 

in use.

Noise measurement results, shown in Table C6, show that personal noise exposures in the woodshop 

were above the NIOSH REL, but below the OSHA noise exposure limits. Depending on the length of 

time powered woodworking equipment are used, exposures could increase and potentially increase 

above OSHA noise exposure limits. Figure B4 shows the time history noise exposure profile in the 

woodshop revealing that sounds levels sometimes exceeded 95 dBA and occasionally reached 100 dBA 

during the use of powered woodworking equipment. These high sound levels were the primary 

contributor to employees’ noise exposures. Employees had both ear plugs and earmuff available for use. 

We learned during the site visit that some employees used noise canceling headphones or earbuds. It 

should be noted that noise canceling headphones and earbuds are not considered hearing protection 

and should not be used for protection from occupational noise exposures. Employees using powered 

woodworking equipment in the woodshop should wear appropriate earmuffs or earplugs for hearing 
B-7

protection. In addition, because noise exposures were above the NIOSH REL, woodshop employees 

should be included in a hearing loss prevention program. The area noise measurement results from the 

employee work area outside the woodshop indicate that exposure would be far below the NIOSH REL 

and OSHA noise exposure limits.

50

60

70

80

90

100

110

Sound Level (dBA)

Time

Figure B4. Time-history noise exposure profile for work in the woodshop.

Radon 

Radon is a radioactive gas that is a product of the breaking down of radioactive elements, such as 

uranium. These radioactive elements are found naturally in different amounts in soil and rock 

throughout the world. Radon gas emitted from soil or rock can enter buildings through cracks or other 

openings in their foundation. Radon levels are typically highest in the basement as this level is closest to 

the rock or soil that is the source of radon. High levels of radon exposure are more typically observed in 

workers in industries like uranium processing. The American Cancer Society (ACS) states that long-term 

exposure to high levels of radon can cause lung cancer [ACS 2015].

Radon levels measured across the 10-day sample period averaged 6 picocuries per liter (pCi/L), ranging

4.6–9.0 pCi/L. Daily averages, shown in Table C7, ranged 5.2–7.6 pCi/L. Figure B5 provides a time 

history of radon levels across the measurement period. Although not substantially different, radon levels 

were slightly higher December 20–21, relative to previous days of measurements. The reason for these 

higher levels is unclear but could be related to slightly less air exchange in the cavern on those days.
B-8

0

1

2

3

4

5

6

7

8

9

10

Radon (pCi/L)

Figure B5: Time-history for radon concentrations over a 10-day period.

Across the United States, background concentrations of radon in outdoor air range from 0.003 to 

2.6 pCi/L and are higher in areas with uranium and thorium deposits or granite formations [DOE 

1995]. According to the EPA map of radon zones, the geographic area where the warehouse is located 

is in a zone where the EPA predicts that the “average indoor radon levels may be less than 2 pCi/L.” 

However, because the cavern workplace is below ground with limited air exchange, it is not surprising 

that background radon levels might be higher than those predicted by EPA for the zone. In addition, 

radon levels can vary within any given zone.

The EPA recommends taking corrective measures when indoor home radon levels exceed 4 pCi/L. 

However, the recommendations and action levels for indoor radon provided by the EPA are not 

directly applicable to a workplace environment. For occupational settings, the OSHA permissible

exposure limit (PEL) is 100 pCi/L for a 40-hour exposure in any work week of seven consecutive days.

None of the radon levels we measured were above the OSHA PEL of 100 pCi/L. Radon 

concentrations were above the EPA AL of 4 pCi/L. However, the EPA AL is not considered an OEL 

but rather a limit intended to protect the general public from exposure to radon in homes and schools. 

The EPA AL was established based, in part, on the risk of lung cancer for a person exposed to 4 pCi/L 

for 7,000 hours per year over a lifetime. In contrast, workplace exposure limits are based on the general 

assumption that employees are exposed for 2,000 hours per year (equivalent to 40 hours per week for 

50 weeks per year).

Methods: Ventilation and Air Exchange

During our second site visit on December 11, we measured air exchange within the cavern workspace 

following procedures specified in ASTM standard E741-11 [2017] “Standard Test Method for 

Determining Air Change in a Single Zone by Means of a Tracer Gas Dilution.” We measured the 
B-9

workplace dimensions (including the office, warehouse, and woodshop areas). We also measured the 

dimensions of overhead doors between the workspace and the main cavern passageway.

We released sulfur hexafluoride (SF6) as a tracer gas in the back of the warehouse space and used 

existing large floor fans and dehumidifier fans to achieve even mixing of air throughout the space. We 

measured SF6 concentrations using tracer gas analyzers in the warehouse, office, and woodshop areas to 

determine the rate at which air is exchanged between the workspace and external main cavern 

passageway. 

We also used a TSI VelociCalc® anemometer to measure air velocities from local exhaust ventilation

(LEV) controls connected to a finish sander and table saw in the woodshop. In addition, we visually 

inspected portable room air cleaners and documented filter type and efficiency.

Results and Discussion: Ventilation and Air Exchange

Ventilation in the cavern workplace included the following: 

• Two ceiling-mounted heat pumps provided heated air to the space. 

• Two industrial dehumidifiers reduced and maintained humidity levels. 

• Three stationary floor fans to circulated air within the space.

• A portable recirculating air filtration unit in the main warehouse area (was not in use during 

site visit).

• A large overhead door measured 18 ft wide by 16 ft high.

• A loading dock door measured 8.3 ft wide by 10 ft high.

• A stationary floor fan in the woodshop directed air from the woodshop toward the 

loading dock area. 

• Two portable recirculated air filtration units located between the woodshop and loading dock. 

• The woodshop had state-of-the-art LEV dust controls and filtration but did not have general 

ventilation to remove dust that escapes LEV capture.

Based on our tracer gas measurements, we calculated that the facility had 0.079 air changes per hour 

(ACH) or one air exchange every 13 hours between the workplace and the main cavern passageway. 

However, it should be noted that the air in the main cavern passageway has the potential to be 

contaminated with exhaust from vehicles driven throughout the cavern. Also, air exchanged between 

the main cavern passageway and the workspace more closely matched the ANSI/ASHRAE Standard 

62.1 definition of transfer air (air moved from one indoor space to another) rather than providing 

ambient air or outdoor air.

To improve overall air quality within the warehouse workspace and woodshop, we recommend 

supplying outdoor air to the company’s warehouse and workshop areas following the specifications of 

ANSI/ASHRAE Standard 62.1 Table 6-1. This would require minimum ventilation rates of 0.06 cubic 

feet per minute per square foot (cfm/ft2) of outdoor air to the warehouse and 0.18 cfm/ft2 of outdoor 

air to the woodshop [ANSI/ASHRAE 2022]. Based on the size of the warehouse and woodshop, 

2,200 cfm of outdoor air would need to be supplied to meet ANSI/ASHRAE 62.1 Table 6.2.2.1 
B-10

specifications (1,980 cfm to the warehouse and 216 cfm to the woodshop). ASHRAE Standard 62.1 

defines requirements for ventilation and applies to spaces intended for human occupancy within 

buildings.

Methods: Evaluation of “Cave Cotton” Mineral Fibers and Oil-like Residue Collected

from Cavern Walls

“Cave Cotton” Mineral Fibers 

Bulk samples of mineral fibers, referred to by employees as “cave cotton,” were collected from the 

cavern wall using tweezers and placed in glass specimen jars. The samples were submitted to determine 

the composition and morphologies using scanning electron microscopy (SEM) and energy dispersive 

X-ray spectroscopy (EDS). For analysis, the bulk samples were directly placed on the standard SEM 

stubs by using the conductive carbon tape. Representative images of the sample were obtained by the 

back scattered detector (BSD) on a Phenom XL SEM in the variable pressure mode (1–60 Pascals) at 

acceleration voltage of 10 and 15 kilovolts. In addition, the elemental composition was determined by 

the integrated EDS detector and Elemental ID software installed on the Phenom XL SEM.

Oil-like Residue

Small pieces of rock that were partially coated with an oil-like residue were placed in glass specimen jars. 

Because of the oil-like nature of the residue, we asked the lab to conduct a screening analysis for volatile 

organic chemicals in the residue. For laboratory analysis, the rock samples were placed in separate jars 

for extraction. For one of the jars, 5 milliliters of toluene were added to cover the rock sample. For the 

other jar, 3 milliliters of methanol were added to cover the rock sample. Each sample jar containing the 

rock sample and extraction agent (as well as toluene and methanol blanks) were shaken for 30 minutes 

to allow sufficient extraction time. Analysis using gas chromatography-mass spectrometry (GC-MS) and 

thin layer chromatography (TLC) was done for each of the samples.

For GC-MS analysis, an aliquot of each sample (and blank) was analyzed using NIOSH Method 

NMAM 2549 [NIOSH 2023]. The samples were modified for liquid injection using multiple injection 

port temperatures and run (hold) times. The analysis was conducted using an Agilent 6890 gas 

chromatograph with an Agilent 5973 mass spectrometer that was operated under electronic ionization

conditions. A HP-1MS fused silica capillary column was used for the analyses. For TLC analysis, the 

extracts were also spotted on TLC plates using both methanol and toluene as the elution solvent.

Results and Discussion: Evaluation of “Cave Cotton” Mineral Fibers and Oil-like

Residue Collected from Cavern Walls

“Cave Cotton” Mineral Fibers 

Figure B5 shows the white-colored translucent fibers on a wall of the cavern. Facility staff referred to 

the fibers as “cave cotton” due to the texture and appearance of the fibers. The analytical laboratory 

reported that the bulk minerals were white/transparent fibers that were readily soluble in water. The 

SEM images show typical structures of fibers with diameters in the range of 3 to 30 μm (Figure B6). 

Elemental analysis showed the presence of magnesium, sulfur, and oxygen in the fibers. The

proportional average calculated atomic weight concentrations for the four different samples analyzed 

were oxygen (61.3), magnesium (19.5), and sulfur (19.2). The atomic weight concentrations suggest that 
B-11

the mineral fiber contained a compound consisting of magnesium sulfate with formula MgSO4, referred 

to as epsomite. 

Figure B5. Mineral fibers on cavern surface. Photo by NIOSH.

Figure B6. Photomicrograph of the mineral fibers magnified 300 times. Photo by NIOSH. 

Epsomite has been known to form on the internal surface of cave walls, particularly limestone caves, on 

magnesium-rich rocks and under dry conditions. It has been referred to as “cave cotton” in its fibrous 

form. Self and Hill [2003] reported on the mechanisms for growth of fibrous aggregates in caves. A 

theoretical study by Giordani et al. [2022] explored whether epsomite fibers could potentially present a 

health risk. Their research on epsomite fibers from a cave in Italy noted that about 25% of the fibers 

were small enough to penetrate the lungs, if airborne. Because of the high solubility of the fibers under 

internal lung conditions, they would not be able to cause damage such as could occur with insoluble 

fibers. However, if the fibers contained other chemicals, these could be released when fibers dissolved. 
B-12

The study authors cautioned that due to the lack of in-vivo, in-vitro, and epidemiological studies, 

additional research was needed to determine actual human toxicological risk.

Because the warehouse has relatively limited amounts of these fibers present on the cavern walls, and 

typical workplace conditions would not cause fibers to become airborne, the fibers should not present a 

risk to employees. However, if fibers needed to be removed from the wall, use a high efficiency 

particulate air (HEPA)-filtered vacuum for removal tasks.

Oil-like Residue 

A brownish-colored oil-like residue was present 

on a few of the cavern walls within the 

warehouse. There were no known external or

internal sources for the residue. The residue had a 

somewhat stratified appearance on the cavern 

wall (Figure B7) suggesting the possibility it could 

be leaching through the cavern rock from an 

underground or above ground source. However, 

the depth of the residue was not known so we 

could not determine whether it extended beneath 

the cavern wall surface or was present primarily 

on the rock surface. It is also possible that the 

residue was a remnant from activities related to its 

former use as a limestone quarry.

During analytical laboratory analysis, the toluene 

extract turned very dark brown. The methanol 

extract turned light yellow. These color changes in the extract indicated that the residue extracted from 

the rock samples was primarily nonpolar (i.e., the electrical charge of the molecules were evenly 

distributed across the molecule). 

Neither the GC-MS nor TLC analyses provided conclusive results. The methanol extract, when injected 

at 320°C during GC-MS analysis, resulted in a few small hydrocarbon peaks, likely in the range of C20

and greater (i.e., the molecule contains 20 or more carbon atoms). The toluene extract, when injected at 

320°C during GC-MS analysis, resulted in a few small peaks, potentially indicating polycyclic 

hydrocarbons with molecular weights greater than 300 atomic mass units. The analysis indicated that 

the components of the oil-like residue were of higher molecular weight than what is typically observed 

using NIOSH Method NMAM 2549 for volatile organic chemical screening. However, due to the lack 

of hydrocarbons in the C10–C15 range, the residue was unlikely to be diesel or crude oil. During TLC 

analysis, the toluene and methanol extracted some highly fluorescing components. The toluene 

extracted more nonpolar compounds. The analysis indicated that the (nonpolar) residue must be of 

higher molecular weight since it did not move on the TLC plate for either the toluene or methanol 

eluting solvent.

Figure B7. Oil-like residue on cavern wall. Photo by 

NIOSH.
B-13

Methods: Illumination Levels 

We used a Sper Scientific company light meter (Model S40020) to measure illumination levels in several 

areas across the facility.

Results and Discussion: Illumination Levels

We measured illumination intensities ranging 62–169 lux in the front painting area. Illumination 

intensities ranged 202–252 lux in the area with the conference and worktables. In the warehouse space, 

illumination intensities ranged from 77 lux (at the border between this facility and the adjacent tenant’s 

space) to 265 lux (in the middle of the second aisle, near the artwork on the floor). OSHA’s minimum 

illumination intensity requirement depends upon the classification of a workspace. For indoor 

warehouses, OSHA’s minimum illumination intensity is 54 lux. For general construction plants and 

shops (including carpentry shops and workrooms), OSHA’s minimum requirement is 110 lux. OSHA 

also has a standard for office space of 320 lux. Our measurements indicated that illumination in the 

warehouse area exceeded OSHA’s minimum limits. To improve visibility in other areas and be aligned 

with OSHA’s specifications, we recommend improving lighting in the painting area to 110 lux and to 

320 lux in areas that used for office-related functions, such as the conference table and computer 

worktables near the conference table.

Methods: Employee Health Assessment 

• We invited all employees working on the day of our second visit to participate in private 

interviews. 

• We collected information about employees’ work history and practices, personal protective 

equipment use, work-related exposures and health symptoms, and relevant medical history 

through these voluntary confidential medical interviews. 

• Work-related health symptoms were defined as health symptoms that reportedly improved away 

from work. 

Results and Discussion: Employee Health Assessment 

All five employees working in the cavern warehouse during our second visit participated in confidential 

medical interviews, including art handlers (n = 2), design preparators (n = 2), and a collection manager 

(n = 1). The median age of employees was 32 (range: 28–43 years). Some employees reported a history 

of smoking or being a current smoker. 

Interviewed employees reported working in the facility a median of 9 months (range: 6 months–4 years 

8 months). All employees reported typically spending 5 days per week and a median of 8 hours per day 

in the workplace (range: 8.0–8.5 hours). Employees sometimes worked outside of the cavern 

warehouse, at hotels or private homes, when installing art exhibits. 

All five interviewed employees reported being exposed to loud noise at work at times. Three employees 

reported wearing hearing protection during the use of saws or other tasks that generated high noise 

levels. Among those reporting using hearing protection, the types of hearing protection reported 

included earmuffs or noise canceling headphones. Two employees reported also being exposed to loud 
B-14

noise outside of work from sources such as power tools, lawn mowers, or leaf blowers. None of the 

five interviewed reported having trouble hearing. 

All five interviewed employees reported one or more health symptom during the past month that 

improved when they were away from work. These symptoms included eye irritation, nasal irritation, 

throat irritation, shortness of breath, cough, headache, lightheadedness or dizziness, fatigue, weakness, 

nausea, and confusion. No employees reported seeking medical attention from a doctor or other 

healthcare provider for these symptoms. Some employees reported a history of allergies in the form of 

hay fever or seasonal allergies. 

Some symptoms reported by employees, such as eye irritation, nasal irritation, throat irritation,

coughing, and shortness of breath, could potentially be associated with exposures to airborne wood 

dust for those employees who used woodworking equipment. Air sampling results for wood dust 

indicated that exposures in the woodshop were at the NIOSH REL and the ACGIH TLV. Levels 

outside the woodshop were well below these levels and not likely to lead to associated health symptoms. 

Air sampling results showed that CO levels were well below OELs. Levels for other parameters (CO2, 

RH, and temperature), typically used to assess IEQ, were all within recommended guidelines. However, 

some of the employees reported health symptoms, such as headaches and respiratory symptoms, which

have been reported previously by employees in buildings with IEQ problems [Brightman et al. 2008; 

Malkin et al. 1996]. These symptoms are nonspecific, meaning they can be caused by many things, and 

they are common. For example, 86%–95% of the general population have one or more of these 

symptoms during any given 2- to 4-week period. The average adult reports a minimum of one symptom 

every 4–6 days [Barsky and Borus 1995]. Further, the average adult has two to three upper respiratory 

infections per year, also causing these nonspecific symptoms [Benninger et al. 2003].

The warehouse did not have running water or a bathroom facility within in the workspace. Employees 

who needed to use a bathroom had to leave the warehouse and walk to facilities available in the 

common area of the cavern. It took about a minute or more to walk to these bathroom facilities. Four 

of the five interviewed employees reported that lack of running water and bathrooms in the warehouse 

impacted their work or health. When asked about these reported health impacts, employees expressed 

concerns related to dehydration (choosing not to drink water because the bathroom was not nearby), 

sanitation, and the inability to quickly access water in the case of accidental exposure to adhesive or 

solvents that were occasionally used in the woodshop or painting area. Adding a portable toilet, 

handwashing station, self-contained emergency eyewash, and bottled water dispenser could help 

alleviate these employee concerns.

Limitations 

This evaluation was subject to limitations. Exposure assessment could only document exposures and 

conditions in the locations evaluated and on the days evaluations occurred. These results may not have 

been representative of conditions during other times. Medical interviews were also subject to similar 

limitations. We were only able to document concerns and symptoms that were reported to us during 

our evaluations by current employees. We were not able to include information from employees who 

had left the workforce or were not present at the time of the evaluation. Interviews may have been 

impacted by selection, recall, and social desirability biases.
B-15

Conclusions 

We found employees’ noise exposures in the woodshop exceeded the NIOSH REL due to noise 

generated during the use of powered woodworking equipment. Wood dust exposures in the woodshop 

could exceed OELs depending on how much time woodworking equipment was used. We 

recommended including woodshop employees in a hearing loss prevention program, which includes 

audiometric testing, proper hearing protection use, and employee training. We also recommended 

improving wood dust capture at the saws. Our measurements indicated that carbon monoxide and 

radon levels were well below OELs.
C-1

Section C: Tables

Table C1. Spot measurement results for carbon monoxide, carbon dioxide, relative humidity, and 

temperature during initial visit 

Measurement location Carbon 

monoxide 

(*ppm)

Carbon 

dioxide 

(*ppm)

Relative 

humidity 

(%)

Temperature 

(°F)

Main hallway near workstation 2.1 1,224 53.2 70.7

Back of main hallway 2.2 1,237 53.6 70.6

Back of second hallway 2.1 1,230 53.8 70.4

Middle of second hallway 2.2 1,218 53.9 70.3

Near front bay door 2.1 1,219 53.8 70.4

Front left side of workspace 2.1 1,240 52.9 68.8

Woodshop 1.8 1,230 57.3 69.1

Cavern parking area outside the workspace 0 560 78.2 65.3

Outdoor parking lot outside the cavern 0 414 38.9 68.0

*parts per million

Table C2. Average, minimum, and maximum carbon monoxide, carbon dioxide, relative humidity, and 

temperature levels during December 11–21, 2018 (measurements taken every 15 minutes)

 Carbon 

monoxide (ppm*) 

Carbon dioxide 

(ppm*) 

Relative 

humidity (%)

Temperature (°F)

Average 0.1 770 51.3 70.0

Minimum 0 657 48.9 69.5

Maximum 0.8 933 53.1 71.2

*parts per million

Table C3. Time-weighted average air sampling results for wood dust

Work area Sample duration 

(minutes)

Concentration 

(*mg/m3) 

Woodshop (personal sample) 349 1.00

Painting area outside woodshop (personal sample) 338 0.22

Employee workstation (area sample) 425 0.13

NIOSH recommended exposure limit (REL) 1 

OSHA permissible exposure limit (PEL) 15

ACGIH threshold limit value (TLV) 1 

*milligrams per cubic meter
C-2

Table C4. Minimum, maximum, and average particle

concentrations (in milligrams per cubic meter) 

PM1 PM2.5 Respirable PM10 Total

Minimum 0.028 0.029 0.032 0.041 0.045

Maximum 0.099 0.106 0.121 0.214 0.309

Average 0.039 0.042 0.046 0.066 0.082

Table C5. Sound level measurement results

Measurement description Sound level (dB*) 

Background noise in woodshop with only the fan operating 65.5

Using miter saw (Festool KS120EB) cutting 1" × 7" pine board 89.9

Using handheld router (Festool OF1400EQ) on 1" × 7" pine board 92.4–93.6

Using handheld router on wood corner pieces 93.4

In painting area when routing occurring in adjacent woodshop 75.6–78.4

Using table saw (SawStop Professional 1.75 horsepower) cutting plywood 85.6

Background noise at table saw with only local exhaust operating 79.8

Background noise at the conference table with woodshop table saw operating 70.7

Background noise at the conference table with woodshop table saw local exhaust on 67.3

Background noise at the conference table with only the fan in the woodshop on 62.0

*decibels

Table C6. Full-shift personal noise measurement results in decibels, A-weighted 

Work area Result using NIOSH 

REL criterion*

Result using OSHA AL

criterion*

Result using OSHA PEL 

criterion†

Woodshop 88 82 80

Painting area outside 

woodshop

75 67 55

Employee workstation 

(area sample)

56 39 ‡ 

Noise exposure limits

(as 8-hour timeweighted averages)

85 85 90

*The criteria for calculating the NIOSH recommended exposure limit (REL) and OSHA action level (AL)

include all sound levels greater than or equal to 80 decibels, A-weighted (dBA).

†The criteria for calculating the OSHA permissible exposure limit (PEL) include all sound levels greater 

than or equal to 90 dBA. 

‡All sounds levels were below 90 dBA; therefore, no sound was integrated to calculate a result.
C-3

Table C7. Daily average radon concentration during

December 11–21, 2018

Date Radon (pCi/L*)

December 11 5.3

December 12 5.5

December 13 5.2

December 14 6.1

December 15 6.5

December 16 6.0

December 17 5.3

December 18 5.4

December 19 6.2

December 20 7.2

December 21 7.6

*picocuries per liter

Table C8. Illumination measurements in work areas

Measurement location Lux

Painting station (middle) 73

Painting station (far end) 169

Painting station (close to office) 62

Far end of occupied space 77

Conference table 202

Worktable (near conference table) 208

Worktable (large table in back) 252

Back of facility 262

Center of warehouse row 2 (middle of artwork) 265
D-1

Section D: Occupational Exposure Limits

NIOSH investigators refer to mandatory (legally enforceable) and recommended OELs for chemical, 

physical, and biological agents when evaluating workplace hazards. OELs have been developed by 

federal agencies and safety and health organizations to prevent 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 if their exposures are maintained below these 

levels. Some may have adverse health effects because of individual susceptibility, a preexisting medical 

condition, or a hypersensitivity (allergy). In addition, some hazardous substances act in combination 

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

employee to produce adverse health effects. Most OELs address airborne exposures, but some 

substances can be absorbed directly through the skin and mucous membranes.

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 short-term 

exposure limits ceiling values. Unless otherwise noted, the short-term exposure limit is a 15-minute 

TWA exposure. It should not be exceeded at any time during a workday. The ceiling limit 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; others are 

recommendations.

• The U.S. Department of Labor OSHA permissible exposure limits (29 CFR 1910 [general 

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

limits. These limits are 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 and the adequacy of methods to identify and control the hazard. NIOSH RELs are 

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

recommends 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.

• Another set of OELs commonly used and cited in the United States is the ACGIH TLVs. The 

TLVs are developed by committee members of this professional organization from a review of 

the published, peer-reviewed literature. TLVs are not consensus standards. They 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 2023].

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

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

Unfallversicherung (Institute for Occupational Safety and Health of the German Social Accident 
D-2

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/GESTIS/GESTIS-Internationale-Grenzwerte-für-chemische-Substanzenlimit-values-for-chemical-agents/index-2.jsp, contains international limits for more than 2,000 

hazardous substances and is updated periodically.

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]). This is true in the absence of a specific OEL. It also is important 

to keep in mind that OELs may not reflect current health-based information. 

When multiple OELs exist for a substance or agent, NIOSH investigators generally encourage 

employers to use the lowest OEL when making risk assessment and risk management decisions.

Carbon Monoxide

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

materials, e.g., gasoline. The initial symptoms of CO poisoning may include headache, dizziness, 

drowsiness, and nausea. These initial symptoms may advance to vomiting, loss of consciousness, and 

collapse if prolonged or high exposures are encountered. Coma or death may occur if high exposures 

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

the hemoglobin to form carboxyhemoglobin (COHb) [ACGIH 2001; NIOSH 1972, 1977, 1979, 2010; 

Proctor et al. 1988].

The NIOSH REL for CO is 35 ppm for an 8-hour TWA exposure, with a ceiling limit of 200 ppm that

should not be exceeded [NIOSH 2010]. The NIOSH REL is designed to protect workers from health 

effects associated with COHb levels in excess of 5% [NIOSH 1972]. The ACGIH recommends a TLV 

of 25 ppm as an 8-hour TWA. This is designed to protect workers from health effects associated with 

COHb levels in excess of 3.5% [ACGIH 2001]. The OSHA PEL for CO is 50 ppm for an 8-hour TWA 

exposure [29 CFR 1910.1000]. 

Wood Dust

Exposure to wood dust has been reported to cause both increases in respiratory symptoms, including 

nasal dryness, irritation, bleeding, obstruction, coughing, wheezing, and sneezing; sinusitis; and 

prolonged colds. These increases have been seen even at mean total dust concentrations below 4 

mg/m3. Reduced mucociliary transport rates have also been reported in workers chronically exposed to 

wood dust, and in one study the reduced rates were related to increasing dust concentrations. These 

effects were not seen following acute inhalation exposure, nor were they seen following inhalation of 

high concentrations of inert plastic spheres with a size distribution similar to that of beech dust. This 

implies that reduce respiratory mucous secretion and transport results from long-term exposure and is 

not caused simply by the mechanical action of the dust, although such irritation may be a contributing 

factor. Nasal mucosa changes have also been reported in woodworkers. Several studies have reported 

decreased ventilatory function, as measured by forced vital capacity and forced expiratory volume in 

one second, among workers exposed to wood dust. Some studies have also shown a significant decrease 
D-3

in woodworkers' lung function over the work shift, although no concentration-response relationship 

was seen [NIOSH 1987a]. 

Wood dust exposure may cause eye and skin irritation and respiratory effects. In industrial settings, 

certain hard woods, such as oak, maple, and walnut, have been linked to nasal cancer [Hathaway et al. 

1991]. Loggers and persons involved in initial wood processing are exposed to irritant chemicals found 

in the bark or sap in the outer part of the tree. They are most affected by primary irritant dermatitis, 

which consists of erythema and blistering [Hathaway et al. 1991]. The adverse health effects that have 

been associated with exposure to wood dust upon which evaluation criteria are based include dermatitis, 

allergic respiratory effects, and mucosal and nonallergenic respiratory effects. NIOSH recommends that 

wood dust be considered a potential occupational carcinogen and that exposures be reduced to the 

lowest feasible level, not to exceed the REL of 1 mg/m3 for both soft and hard woods [NIOSH 2010]. 

ACGIH has a TLV of 0.5 mg/m3 for Western Red Cedar and 1 mg/m3 for all other wood species 

[ACGIH 2023]. There is currently no specific OSHA PEL for wood dust. The OSHA PEL for total 

particulate not otherwise regulated is 15.0 mg/m3 and 5.0 mg/m3 for the respirable fraction, determined 

as 8-hour averages [29 CFR 1910.1000]. 

Noise

Noise-induced hearing loss (NIHL) is an irreversible condition that progresses with noise exposure. 

NIHL is caused by damage to the nerve cells of the inner ear and, unlike some other types of hearing 

disorders, cannot be treated medically [AIHA 2022]. Approximately 25% of U.S. workers have been 

exposed to hazardous noise [Kerns et al. 2018] and more than 22 million U.S. workers are estimated to 

be exposed to workplace noise levels above 85 dBA [Tak et al. 2009]. NIOSH estimates that workers 

exposed to an average daily noise level of 85 dBA over a 40-year working lifetime have an 8% excess 

risk of material hearing impairment. This excess risk increases to 25% for an average daily noise 

exposure of 90 dBA [NIOSH 1998]. NIOSH defines material hearing impairment as an average of the 

HTLs for both ears that exceeds 25 dB at frequencies of 1 kilohertz (kHz), 2 kHz, 3 kHz, and 4 kHz.

Although hearing ability commonly declines with age, exposure to excessive noise can increase the rate 

of hearing loss. In most cases, NIHL develops slowly from repeated exposure to noise over time, but 

the progression of hearing loss is typically the greatest during the first several years of noise exposure 

[Rosler 1994]. NIHL can result from short duration exposures to high noise levels or even from a single 

exposure to an impulsive noise or a continuous noise, depending on the intensity of the noise and the 

individual’s susceptibility to NIHL [AIHA 2022]. Noise exposed workers can develop substantial NIHL 

before it is clearly recognized. Even mild hearing losses can impair one’s ability to understand speech 

and hear many important sounds. In addition, some people with NIHL also develop tinnitus. Tinnitus 

is a condition in which a person perceives hearing sound in one or both ears, but no external sound is 

present. Persons with tinnitus often describe hearing ringing, hissing, buzzing, whistling, clicking, or 

chirping like crickets. Tinnitus can be intermittent or continuous and the perceived volume can range 

from soft to loud. Currently, no cure for tinnitus exists.

Noise measurements are usually reported as dBA, A-weighting is used because it approximates the 

“equal loudness perception characteristics of human hearing for pure tones relative to a reference of 

40 dB at a frequency of 1 kHz” and is considered to provide a better estimation of hearing loss risk than 
D-4

using unweighted or other weighting measurements [Murphy et al. 2022]. The dB unit is dimensionless, 

and it represents the logarithmic ratio of the measured sound pressure level to an arbitrary reference 

sound pressure of 20 micropascals, which is defined as the threshold of normal human hearing at a 

frequency of 1 kHz. Because the dB is logarithmic, an increase of 3 dB is a doubling of the sound 

energy, an increase of 10 dB is a 10-fold increase, and an increase of 20 dB is a 100-fold increase in 

sound energy. Noise exposures expressed in dB or dBA cannot be averaged using the arithmetic mean.

Workers exposed to noise should have baseline and yearly hearing tests (audiograms) to evaluate their 

hearing thresholds and determine whether their hearing has changed over time. Hearing testing should 

be done in a quiet location, such as an audiometric test booth, where background noise does not 

interfere with accurate measurement of hearing thresholds. In workplace hearing conservation 

programs, hearing thresholds must be measured at frequencies of 0.5 kHz, 1 kHz, 2 kHz, 3 kHz, 4 kHz, 

and 6 kHz. NIOSH also recommends testing be done at 8 kHz [NIOSH 1998].

The OSHA hearing conservation standard requires analysis of hearing changes from baseline hearing 

thresholds to determine if a standard threshold shift (STS) has occurred. OSHA defines an STS as a 

change in hearing threshold relative to the baseline hearing test of an average of 10 dB or more at 

2 kHz, 3 kHz, and 4 kHz in either ear [29 CFR 1910.95]). If an STS occurs, the company must 

determine if the hearing loss also meets the requirements to be recorded on the OSHA Form 300 Log 

of Work-Related Injuries and Illnesses [29 CFR 1904.1]. In contrast to OSHA, NIOSH defines a 

significant threshold shift as an increase in the hearing threshold level of 15 dB or more, relative to the 

baseline audiogram, at any test frequency in either ear measured twice in succession [NIOSH 1998].

Hearing test results are often presented in an audiogram, which is a plot of an individual’s hearing 

thresholds (y-axis) at each test frequency (x-axis). Hearing threshold levels (HTLs) are plotted such that 

fainter sounds are shown at the top of the y-axis, and more intense sounds are plotted below. Typical 

audiograms show HTLs from −10 or 0 dB to about 100 dB. Lower frequencies are plotted on the left 

side of the audiogram, and higher frequencies are plotted on the right. NIHL often manifests itself as a 

“notch” at 3 kHz, 4 kHz, or 6 kHz, depending on the frequency spectrum of the workplace noise and 

the anatomy of the individual’s ear [ACOM 1989; Mirza et al. 2018; Osguthorpe and Klein 1991; 

Schlaucha and Carneya 2011; Suter 2002]. A notch in an individual with normal hearing may indicate 

early onset of NIHL. A notch is defined as the frequency where the HTL is preceded by an 

improvement of at least 10 dB at the previous test frequency and followed by an improvement of at 

least 5 dB at the next test frequency.

NIOSH has an REL for noise of 85 dBA as an 8-hour TWA. For calculating exposure limits, NIOSH 

uses a 3-dB time/intensity trading relationship, or exchange rate. Using this criterion, an employee can 

be exposed to 88 dBA for no more than 4 hours, 91 dBA for 2 hours, 94 dBA for 1 hour, 97 dBA for 

0.5 hours, etc. Exposure to impulsive noise should never exceed a peak level of 140 dBA. For extended 

work shifts, NIOSH adjusts the REL to 84.5 dBA for a 9-hour shift, 84.0 dBA for a 10-hour shift, 

83.6 dBA for an 11-hour shift, and 83.2 dBA for a 12-hour work shift. When noise exposures exceed 

the REL, NIOSH recommends the using hearing protection and implementing a hearing loss 

prevention program [NIOSH 1998].
D-5

The OSHA noise standard specifies a PEL of 90 dBA and an AL of 85 dBA, both as 8-hour TWAs. 

OSHA uses a less conservative 5-dB exchange rate for calculating the PEL and AL. Using the OSHA 

criterion, an employee may be exposed to noise levels of 95 dBA for no more than 4 hours, 100 dBA 

for 2 hours, 105 dBA for 1 hour, 110 dBA for 0.5 hours, etc. Exposure to impulsive noise must not 

exceed 140 dB peak noise level. OSHA does not adjust the PEL for extended work shifts. However, the 

AL is adjusted to 84.1 dBA for a 9-hour shift, 83.4 dBA for a 10-hour shift, 82.7 dBA for an 11-hour 

shift, and 82.1 dBA for a 12-hour work shift. OSHA requires implementation of a hearing conservation 

program when noise exposures exceed the AL [29 CFR 1910.95]. 

An employee’s daily noise dose, based on the duration and intensity of noise exposure, can be 

calculated according to the formula: Dose = 100 × (C1/T1 + C2/T2 + ... + Cn/Tn), where Cn indicates 

the total time of exposure at a specific noise level, and Tn indicates the reference exposure duration for 

which noise at that level becomes hazardous. A noise dose greater than 100% exceeds the noise 

exposure limit.

Radon

OSHA has two relevant OELs for radon. The OSHA PEL for radon gas is 100 pCi/L or 

3,700 becquerels per cubic meter (Bq/m3), averaged over 40 hours in any work week of 7 consecutive 

days. However, because radon is a radioactive material, the OSHA whole body ionizing radiation dose 

limits also apply. The OSHA whole body ionizing radiation dose limit is 1.25 roentgen equivalent man 

(rem) or 12.5 millisieverts (mSv) per quarter. Given that there are four quarters per year, this implies 

that no one should receive a dose larger than 5 rem (50 mSv) in a year. This is the same as the National 

Council on Radiation Protection and Measurements (NCRP) recommended dose limit of 5 rem 

(50 mSv) [NCRP 1993]. Measuring radon gas concentrations alone are not sufficient to assess 

compliance with the OSHA ionizing radiation dose limits. Instead, dose modeling based on the radon 

gas concentrations must be done.

Other agencies also have recommendations for radon gas and radon progeny. NIOSH has an REL for 

radon progeny in underground mines of 1-working-level-month per year (WLM/yr). This REL is an 

upper limit of cumulative exposure; however, NIOSH recommends that exposures should be reduced 

to the lowest feasible level [NIOSH 1987b]. EPA has an action level of 4 pCi/L (148 Bq/m3) for radon 

gas in homes and schools.
E-1

Section E: References

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E-2

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E-3

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E-4

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Promoting productive workplaces through safety 

and health research

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