Environmental Technology Verification 

Biological Inactivation Efficiency by HVAC 

In-Duct Ultraviolet Light Systems 

American Ultraviolet Corporation, DC24-6-120 

Prepared by 

Research Triangle Institute 

Under a Cooperative Agreement with the 

U.S. Environmental Protection Agency 
 American Ultraviolet Corporation, DC24-6-120 Duct Sterilizer 

U.S. Environmental Protection Agency 

THE ENVIRONMENTAL TECHNOLOGY VERIFICATION 

PROGRAM 

ETV Joint Verification Statement 

TECHNOLOGY TYPE: GENERAL VENTILATION AIR CLEANERS 

APPLICATION: BIOLOGICAL INACTIVATION EFFICIENCY BY 

HVAC IN-DUCT ULTRAVIOLET LIGHT 

SYSTEMS 

TECHNOLOGY NAME: DC24-6-120 

COMPANY: American Ultraviolet Corporation 

ADDRESS: 212 S Mount Zion Road 

Lebanon, IN 46052 

PHONE: 

FAX: 

800-288-9288, 

ext. 201 

765-483-9525 

WEB SITE: http://www.americanultraviolet.com 

E-MAIL: mstines@auvco.com 

The U.S. Environmental Protection Agency (EPA) has created the Environmental Technology 

Verification (ETV) Program to facilitate the deployment of innovative or improved environmental 

technologies through performance verification and dissemination of information. The goal of the ETV 

Program is to further environmental protection by accelerating the acceptance and use of improved and 

cost-effective technologies. ETV seeks to achieve this goal by providing high-quality, peer-reviewed data 

on technology performance to those involved in the design, distribution, financing, permitting, purchase, 

and use of environmental technologies. 

ETV works in partnership with recognized standards and testing organizations; stakeholder groups, which 

consist of buyers, vendor organizations, permitters, and other interested parties; and with the full 

participation of individual technology developers. The program evaluates the performance of innovative 

technologies by developing test plans that are responsive to the needs of stakeholders, conducting field or 

laboratory tests (as appropriate), collecting and analyzing data, and preparing peer-reviewed reports. All 

evaluations are conducted in accordance with rigorous quality assurance protocols to ensure that data of 

known and adequate quality are generated and that the results are defensible. 

The Air Pollution Control Technology Verification Center (APCT Center) is operated by RTI 

International (RTI), in cooperation with EPA’s National Risk Management Research Laboratory. The 

S-1
 American Ultraviolet Corporation, DC24-6-120 Duct Sterilizer 

APCT Center conducts verifications of technologies that clean air in ventilation systems, including induct ultraviolet (UV) light systems. This verification statement provides a summary of the test results for 

the American Ultraviolet Corporation DC24-6-120 Duct Sterilizer. 

VERIFICATION TEST DESCRIPTION 

All tests were performed in accordance with RTI’s “Bioaerosol Inactivation Efficiency by HVAC In-Duct 

Ultraviolet Light Air Cleaner", a supplement to "Test/Quality Assurance Plan for Biological and Aerosol 

Testing of General Ventilation Air Cleaners" which was approved by EPA. Testing for biological 

inactivation was performed using three organisms − two bacteria (Bacillus atrophaeus and Serratia 

marcescens) and one bacterial virus (MS2). To model use in a heating, ventilation and air-conditioning 

(HVAC) system, RTI used a test duct designed for testing filtration and inactivation efficiencies of 

aerosol, bioaerosol, and chemical challenges. 

The testing was conducted in the test duct operated following procedures in the ANSI/ASHRAE 

(American National Standards Institute/American Society of Heating, Refrigerating and Air-Conditioning 

Engineers) Standard 52.2-1999, Method of Testing General Ventilation Air-Cleaning Devices for 

Removal Efficiency by Particle Size. The air flow rate through the duct during this testing was 0.93 m3

/sec 

(1970 cfm). This flow creates a typical air velocity (492 fpm) in the duct, and has been used extensively 

in prior testing of air cleaning devices in this rig. The air temperature entering the device was 

approximately 23 °C. Air flow rate and temperature can have an impact on lamp performance, and the 

values used in this testing are consistent with vendor specifications. Prior to testing the device, the UV 

lamps were operated for a standard 100-hr “burn-in” period. 

There are separate runs for each of the three challenge bioaerosols which were injected upstream of the 

device. The upstream challenge was ~ 2 x 104

 CFU or PFU/ft3. A no-light test was performed with the 

UV lights turned off, to determine the microorganism loss that would occur simply as the result of 

deposition in the test duct, and as the result of kill caused by the physical rigors of flowing through the 

device. The performance of the device was then reported as the device’s efficiency in inactivating the 

organism with the light on, corrected to account for the loss of organisms observed in the absence of UV 

light. 

Additional secondary measurements included: 

• The direct total power consumption by the lamp and ballast, the pressure drop across the device 

(impacting air handler requirements), and the temperature rise through the unit, if any (impacting 

cooling coil energy consumption). 

• A single measurement of the intensity of 254 nm UV radiation (μW/cm2

) at a point 161 cm (63 in.) 

upstream from the lamps, to demonstrate that the lamps were functioning and to provide a test 

reference value for the laboratory for documentation purposes. 

Verification testing of the American Ultraviolet Corporation DC24-6-120 began on July 31, 2007 at the 

test facilities of RTI and was completed on August 21, 2007. 

VERIFIED TECHNOLOGY DESCRIPTION 

The American Ultraviolet Company’s DC24-6-120 is part of the DC Series of in-line duct sterilizers that 

are designed to install into air duct sections to position high output UVC (short-wave ultraviolet radiation, 

in the "C" band - 200 to 280 nanometers) lamp(s) perpendicular to passing airflow for “pass-by” air 

sterilization purposes as well as surface sterilization. The ballast enclosure mounts directly to the duct 

S-2
 American Ultraviolet Corporation, DC24-6-120 Duct Sterilizer 

exterior with lamp(s) protruding into the duct section through a cutout in the duct wall. Type 304 stainless 

steel construction is utilized for long life. Outdoor ballast enclosures are available as an option. The 

SBL415 High Output UVC Lamp is used in the system. 

VERIFICATION RESULTS 

The American Ultraviolet Corporation DC24-6-120 achieved the biological inactivation efficiency tests 

presented in Table 1. 

Table 1. Inactivation Efficiency, % 

Spore form of 

bacteria 

(B. atrophaeus) 

Vegetative bacteria 

(S. marcescens) 

Bacterial virus 

(MS2 

bacteriophage) 

Inactivation 

efficiency (UV 

light on), % 

98 ≥ 99.5a

 99 

a – the value 99.5 represents a 95% confidence limit for S. marcescens. There were no downstream counts 

measured. 

The irradiance was measured as 6290 μW/cm2 at 161 cm (63 in.) upstream from the lamps with an 

airflow of 0.93 m3

/sec (1970 cfm). The mean dosage was calculated as 23,600 μW-s/cm2 with a range of 

19,900 – 29,000 μW-s/cm2 . The system had six lamps that were burned in for 100 hours prior to 

measurements. The spore form of the bacteria B. atrophaeus is more resistant to being killed by UV light 

(irradiation) than the vegetative bacteria S. marcescens. 

The APCT Center's quality manager reviewed the test results and the quality control data and concluded 

that the data quality objectives given in the approved test/QA plan were attained. 

This verification statement addresses the biological inactivation efficiency. Users of this technology may 

wish to consider other performance parameters such as service life and cost when selecting an in-duct UV 

system for bioaerosol control. 

Original signed by Sally Gutierrez, 

Sally Gutierrez 

Director 

01/17/08

Date 

Original signed by Andrew Trenholm,

 Andrew R. Trenholm 

Director 

 01/10/08 

Date 

National Risk Management Research Laboratory 

Office of Research and Development 

United States Environmental Protection Agency 

APCT Center 

RTI International 

NOTICE: ETV verifications are based on an evaluation of technology performance under specific, predetermined 

criteria and the appropriate quality assurance procedures. EPA and RTI make no express or implied warranties as to 

the performance of the technology and do not certify that a technology will always operate as verified. The end user 

is solely responsible for complying with any and all applicable federal, state, and local requirements. Mention of 

commercial product names does not imply endorsement. 

S-3
Environmental Technology Verification 

Biological Inactivation Efficiency by HVAC 

In-Duct Ultraviolet Light Systems 

American Ultraviolet Corporation, DC24-6-120 

Prepared by: 

Research Triangle Institute 

Engineering and Technology Unit

Research Triangle Park, NC 27709 

EPA Cooperative Agreement CR 831911-01 

EPA Project Manager 

Michael Kosusko 

Air Pollution Prevention and Control Division 

National Risk Management Research Laboratory

Office of Research and Development 

U.S. Environmental Protection Agency 

Research Triangle Park, NC 27711 

i 
NOTICE 

This document was prepared by RTI International* (RTI) with partial funding from Cooperative 

Agreement No. CR 831911-01 with the U.S. Environmental Protection Agency (EPA). The document 

has been subjected to RTI/EPA’s peer and administrative reviews and has been approved for publication. 

Mention of corporation names, trade names, or commercial products does not constitute endorsement or 

recommendation for use of specific products. 

FOREWORD 

The Environmental Technology Verification (ETV) Program, established by the U.S. Environmental 

Protection Agency (EPA), is designed to accelerate the development and commercialization of new or 

improved technologies through third-party verification and reporting of performance. The goal of the 

ETV Program is to verify the performance of commercially ready environmental technologies through the 

evaluation of objective and quality-assured data so that potential purchasers and permitters are provided 

with an independent and credible assessment of the technology that they are buying or permitting. 

The Air Pollution Control Technology Verification Center (APCT Center) is part of the EPA’s ETV 

Program and is operated as a partnership between RTI International (RTI) and EPA. The center verifies 

the performance of commercially ready air pollution control technologies. Verification tests use approved 

protocols, and verified performance is reported in verification statements signed by EPA and RTI 

officials. 

AVAILABILITY OF REPORT 

Copies of this verification report are available from 

$ Research Triangle Institute 

Engineering and Technology Unit 

PO Box 12194 

Research Triangle Park, NC 27709-2194 

$ U.S. Environmental Protection Agency 

Air Pollution Prevention and Control Division, E343-02 

109 T.W. Alexander Drive 

Research Triangle Park, NC 27711 

Web site: http://www.epa.gov/etv/verifiedtechnologies.html 

*

 RTI International is a trade name of Research Triangle Institute. 

ii 
TABLE OF CONTENTS 

ETV Joint Verification Statement .............................................................................................................S-1 

Notice .........................................................................................................................................................ii 

Foreword ......................................................................................................................................................ii 

Availability of Report ...................................................................................................................................ii 

Table of Contents.........................................................................................................................................iii 

Acronyms/Abbreviations ............................................................................................................................. iv 

Acknowledgments......................................................................................................................................... v 

1.0 Introduction...................................................................................................................................... 1 

2.0 Technology Description................................................................................................................... 2 

3.0 Test Design and Procedure .............................................................................................................. 3 

4.0 Quality Assurance/Quality Control.................................................................................................. 6 

5.0 Test Results...................................................................................................................................... 8 

6.0 Limitations and Applications........................................................................................................... 9 

7.0 References........................................................................................................................................ 9 

FIGURES 

Figure 2-1. Ballast box installed on the outside of the test rig..................................................................... 2 

Figure 2-2. Device installed inside the test rig............................................................................................. 2 

Figure 3-1. Schematic of test duct. .............................................................................................................. 3 

TABLES 

Table 2-1. Vendor-Supplied Specifications of the DC24-6-120.................................................................. 2

Table 4-1. DQOs for Biological Aerosols ................................................................................................... 7 

Table 5-1. Inactivation Efficiency ............................................................................................................... 8 

Table 5-2. Other Information for the DC24-6-120 ...................................................................................... 8 

iii 
ACRONYMS/ABBREVIATIONS 

A amp(s) 

ANSI American National Standards Institute 

APCT Center Air Pollution Control Technology Verification Center 

ARTI Air-Conditioning and Refrigeration Technology Institute, Inc. 

ASHRAE American Society of Heating, Refrigerating and Air-Conditioning Engineers 

ASME American Society of Mechanical Engineers 

B Bacillus 

BG Bacillus atrophaeus (formerly B. subtilis var niger and Bacillus globigii) 

C Celsius 

cfm cubic feet per minute 

CFU colony forming unit(s) 

cm centimeter 

CV coefficient of variance 

DQO data quality objective 

E Escherichia 

EPA U.S. Environmental Protection Agency 

ETV environmental technology verification 

F Fahrenheit 

fpm feet per minute 

HEPA high efficiency particulate air 

HVAC heating, ventilation and air conditioning 

in. inch(es) 

J joule(s) 

L liter(s) 

m meter(s) 

mm millimeter(s) 

mL milliliter(s) 

min minute(s) 

Fm micrometer(s) 

nm nanometer(s) 

QA quality assurance 

QC quality control 

QMP quality management plan 

QSA quality system audit 

Pa pascal(s) 

PFU plaque forming unit(s) 

psig pounds per square inch gauge 

RMS root mean square 

RTI Research Triangle Institute 

S Serratia 

s second(s) 

TSA technical systems audit 

TTEP Technology Testing and Evaluation Program 

UV ultraviolet 

UVC Short-wave ultraviolet radiation, in the "C" band (200 to 280 nanometers) 

iv 
ACKNOWLEDGMENTS

The authors acknowledge the support of all of those who helped plan and conduct the verification 

activities. In particular, we would like to thank Mike Kosusko, EPA’s Project Manager, and Paul Groff, 

EPA’s Quality Assurance Manager, both of EPA’s National Risk Management Research Laboratory in 

Research Triangle Park, NC. We would also like to acknowledge the assistance and participation of 

American Ultraviolet Corporation personnel who supported the test effort. 

For more information on the DC24-6-120, contact: 

Mr. Meredith C. Stines, President/CEO 

American Ultraviolet 

212 S Mount Zion Road 

Lebanon, IN 46052 

Phone: 800-288-9288 ext.201 

Fax: 765-483-9525 

mstines@auvco.com 

www.americanultraviolet.com 

For more information on RTI’s ETV program, contact 

Debbie Franke 

Research Triangle Institute 

PO Box 12194 

Research Triangle Park, NC 27709-2194 

Telephone: (919) 541-6826 

Email: dlf@rti.org 

v 
1.0 INTRODUCTION 

This report reviews testing performed for bioaerosol inactivation efficiency of the American Ultraviolet 

Company’s DC24-6-120. Environmental Technology Verification (ETV) Program testing of this 

technology/product was conducted by RTI's Air Pollution Control Technology Verification Center 

(APCT Center) from July 31 to August 21, 2007. The testing followed the Bioaerosol Inactivation 

Efficiency by HVAC In-Duct Ultraviolet Light Air Cleaners, Supplement to the APCT Center Test/QA 

Plan for Biological and Aerosol Testing of General Ventilation Air Cleaners1

. 

Section 2 presents a description of the American Ultraviolet Company’s DC24-6-120. Section 3 

documents the procedures and methods used for the test and the conditions over which the test was 

conducted. Section 4 provides information on the quality assurance (QA) and quality control (QC). The 

results of the test are summarized and discussed in Section 5 with limits and applications in Section 6. 

There is a performance summary in Section 7 and references in Section 8. 

This report contains summary information and data from the test as well as the verification statement. 

Complete documentation of the test results is provided in a separate data package and audit of data quality 

report. These reports include the raw test data from product testing and supplemental testing, equipment 

calibrations results, and QA/QC activities and results. Complete documentation of QA/QC activities and 

results, raw test data, and equipment calibrations results are retained in RTI’s files for seven years. 

This ETV testing focuses on ultraviolet (UV) light systems that are mounted in the heating, ventilation 

and air conditioning (HVAC) ducting (in-duct UV light systems) and that operate on a “fly-through” 

basis. That is, they are designed to destroy bioaerosols in the flowing air stream as it passes through the 

device. This is distinguished from UV devices that are designed to treat specific surfaces within the 

HVAC system, in particular, the cooling coils and the condensate drain pan, to prevent biological growth 

on those surfaces. This program tests inactivation of airborne bioaerosols; inactivation of microorganisms 

on surfaces is not evaluated. 

The bioaerosol tests were conducted using three organisms, consisting of two bacteria (spore-form of 

Bacillus atrophaeus and the vegetative bacterium Serratia marcescens) and one bacterial virus (MS2) that 

cover the range of potential interest for indoor air quality applications. These organisms were selected 

because of their representative sizes and shapes, and susceptibility to UV inactivation. Generally, 

vegetative bacteria are readily killed and bacterial spores are more difficult. The spore form of the 

bacteria Bacillus atrophaeus (formerly B. subtilis var. niger and Bacillus globigii or BG) was used to 

represent gram-positive spore-forming bacteria. The BG spore is elliptically shaped with dimensions of 

0.7 to 0.8 by 1 to 1.5 μm. Serratia marcescens was used to represent rod-shaped gram-negative bacteria. 

S. marcescens is 0.5 to 0.8 by 0.9 to 2.0 μm. 

The bacterial virus (bacteriophage) MS2, having approximately the same aerosol characteristics as a 

human virus, was used as a surrogate for the viruses of similar and larger size and shape. Although the 

individual virus particles are in the 0.02 – 0.03 μm size range, the test particle size for the virus tests 

spanned a range of sizes (polydispersed bioaerosol) in the micron range. This test was not designed to 

study the inactivation efficiencies for individual virus singlets; rather, it was designed to determine the 

inactivation efficiencies for virus particles as they are commonly found indoors. A representative 

challenge would be a polydispersed aerosol containing the bacteriophage because: 

$ The aerosols created from sneezing and coughing vary in size from < 1 to 20 μm, but the largest 

particles settle out and only the smaller sizes remain in the air for extended periods for potential 

removal by an air cleaner; 2 

1
Table 2-1. Vendor-Supplied Specifications of the DC24-6-120 

Attribute Specification 

Total power for the lamp (watts) 60 watts per lamp, total of 360 watts 

Total UVC power for the lamp (watts) Estimated 22 UVC watts per lamp 

Irradiance (output) of the lamp, give distance 

and other information (e.g., airflow) (W/cm2

) 

1262μW/cm2 at 1 meter distance (total) 

[400 fpm, 7.2 °C (45 °F) airflow] 

Dosage (J/cm2 or W-s/cm2) N/A 

Ballast root mean square (RMS) voltage and Available as 120/230/277 VAC 

current 3.45/2.10/1.80 amps total per 6-lamp fixture 

Dimensions of the lamp 534mm / 53.4 cm (21.03 in.) arc Length 

Dimensions of the ballast box 61 cm (24 in.) long x 15.2 cm (6 in.) wide x 11.6 (4.56 in.) 

tall 

Configuration six-lamp unit w/ ballasts mounted in enclosure located out of 

airflow 

Other lamp characteristics N/A 

$ For some viruses (e.g., Coxsackie virus), low numbers of viruses have been found associated with the 

smallest particles;3

 and 

$ Nearly all 1 - 2 μm particles are deposited in the respiratory tract, while larger particles may not be 

respired. 

2.0 TECHNOLOGY DESCRIPTION 

The American Ultraviolet Company’s DC24-6-120 is part of the DC Series in-line duct sterilizers that are 

designed to install into air duct sections to position high output UVC (short-wave ultraviolet radiation, in 

the "C" band - 200 to 280 nanometers) lamp(s) perpendicular to passing airflow for “pass-by” air 

sterilization purposes as well as surface sterilization. The ballast enclosure mounts directly to the duct 

exterior with lamp(s) protruding into the duct section through a cutout in the duct wall. Type 304 stainless 

steel construction utilized for long life. Outdoor ballast enclosures are available as an option. The SBL415 

High Output UVC Lamp is used in the system. 

Table 2-1 provides information on the system as supplied by the vendor. Figures 2-1 and 2-2 provide 

views of the device as tested, installed in accordance with the manufacturer’s specifications. 

2
Figure 2-1. Ballast box installed on the 

outside of the test rig (on right). The 

device is also visible. 

Figure 2-2. Device installed inside the test 

rig. There are six lamps and three support rods. 

3.0 TEST DESIGN AND PROCEDURES 

3.1 Operation of the Test Duct 

The testing was conducted in the test duct shown schematically in Figure 3-1. The test section of the duct 

is 0.61 m by 0.61 m (24 in. by 24 in.). The locations of the major components, including the sampling 

probes, the device section (where the UV device is installed), and the aerosol generator (site of bioaerosol 

injection) are shown. The test duct is operated following procedures in the ANSI/ASHRAE (American 

National Standards Institute/American Society of Heating, Refrigerating and Air-Conditioning Engineers) 

Standard 52.2-1999, Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency 

by Particle Size. 4 

Figure 3-1. Schematic of test duct. UV system is placed in device section. 

While Figure 3-1 shows the test duct without recirculation, during testing, the duct may be operated with 

or without recirculation. The decision for recirculation mode is based on building HVAC considerations. 

Because of the high efficiency particulate air (HEPA) filters at the beginning and the end of the duct, the 

recirculation mode does not affect the test data as long as all other criteria are met. 

3
The air flow rate through the duct during this testing was 0.93 m3

/sec (1970 cfm). This flow creates a 

typical air velocity (492 fpm) in the duct, and has been used extensively in prior testing of air cleaning 

devices in this rig. The air temperature entering the device was approximately 23 °C. Air flow rate and 

temperature can have an impact on lamp performance, and the values used in this testing are consistent 

with vendor specifications. As explained in the VanOsdell and Foarde (2002)5

 report for the AirConditioning and Refrigeration Technology Institute (ARTI), lamps are designed for an optimal 

temperature, and either higher or lower values may lower the irradiance. 

Prior to testing the device, the UV lamps were operated for a standard 100-hr “burn-in” period. 

There are separate runs for each of the three challenge bioaerosols which are prepared as described in 

Section 3.2 and injected upstream of the device. The upstream challenge was ~ 2 x 104

 CFU or PFU/ft3. 

A no-light test was performed with the UV lights turned off, to determine the microorganism loss that 

would occur simply as the result of deposition in the test duct, and as the result of kill caused by the 

physical rigors of flowing through the device. See Section 4.3 for the acceptable range of the penetration 

for this test. As discussed later, the performance of the device was then reported as the device’s efficiency 

in inactivating the organism with the light on, corrected to account for the loss of organisms observed in 

the absence of UV light. 

In addition to the measurement of the concentration of culturable organisms upstream and downstream of 

the device, there were secondary measurements that were not included in the verification statement. These 

include: 

• The direct total power consumption by the lamp and ballast, the pressure drop across the device 

(impacting air handler requirements), and the temperature rise through the unit, if any (impacting 

cooling coil energy consumption). 

• A single measurement of the intensity of 254 nm UV radiation (μW/cm2

) at a point 161 cm (63 in.) 

upstream from the lamps, to demonstrate that the lamps were functioning and to provide a test 

reference value for the laboratory for documentation purposes. 

3.2 Preparation and Generation of Bioaerosol Challenges 

The bioaerosol tests were conducted as described in the test/QA plan supplement using three organisms −

two bacteria (Bacillus atrophaeus and Serratia marcescens) and one bacterial virus (MS2). The selection 

of the bioaerosols was discussed in Section 1. 

The microbial challenge suspensions were prepared by inoculating the test organism onto solid or into 

liquid media, incubating the culture until mature, wiping organisms from the surface of the pure culture 

(if solid media), and eluting them into sterile fluid to a known concentration to serve as a stock solution. 

The organism preparation was then diluted into sterile nebulizing fluid. The nebulizing fluid was 

composed of salts (buffering), peptone, and antifoam (S. marcescens only). The composition of the 

nebulizing fluid should have provided a protective effect similar to organic matter (dirt, debris, etc.) for 

the S. marcescens and possibly the MS2 against the inactivation of the UVC. Based on the VanOsdell 

and Foarde (2002)5

 report, little or no effect was anticipated for the B. atrophaeus as spores were found to 

be relatively unaffected by protective factors. The nebulizing fluid was quantified on trypticase soy agar 

to enumerate the bacteria. 

The bacteriophage challenge was prepared by inoculating a logarithmic phase broth culture of the host 

4
bacteria (E. coli) with bacteriophage and allowing it to multiply overnight or until the majority of the host 

bacteria were lysed (ruptured or broken down). The mixture was processed to collect and concentrate the 

bacteriophage. Then, the bacteriophage stock was filter sterilized (0.2 μm) to remove the bacteria. The 

bacteriophage stock was used as the challenge aerosol. The concentration of the bacteriophage stock was 

approximately 1 x 109

 or higher plaque forming units (PFU)/mL. The virus assay used a standard double 

agar layer plaque assay, in which host cell Escherichia coli C3000 (ATCC 15597) in the log phase of 

growth and serial dilutions of the MS2 virus stock (ATCC 15597-B1) were combined and top agar added 

and then poured onto bottom agar plates.6

 After incubation, at least overnight, at 37 °C, plaques (loci of 

infection) were counted against an opaque lawn of host cell E. coli C3000. 

The challenge organism suspensions were aerosolized using a Collison nebulizer (BGI, Waltham, MA) at 

15 psi air pressure. The Collison nebulizer generated droplets with an approximate volume mean 

diameter of 2 μm. The particle diameter after the water evaporated depended on the solids content of the 

suspension and the size of the suspended particles. Prior experience has shown that the bacterial 

organism aerosols generated by this procedure are primarily singlets. 

3.3 Sampling the Bioaerosols 

All the bioaerosols were collected in liquid impingers, AGI-4 (Ace Glass Inc., Vineland, NJ). Because 

exposure to UV radiation is a common environmental hazard, cells have developed a number of repair 

mechanisms to counteract UV-induced damage that must be considered when experimentally measuring 

UV effects. Collecting in impinger fluid maximized the collection of damaged organisms. After sampling, 

the impinger fluid was plated and incubated at appropriate times and temperatures for the test organism 

being used. To quantify the microbial counts, the plates were incubated at the appropriate temperature 

and time for the test organism (overnight to a week). Colonies or plaques were counted. 

3.4 Bioaerosol Control Efficiency Calculation 

The efficiency of the device for inactivating airborne bioaerosols was then calculated as: 

Airborne Inactivation Efficiency (%) = 100 (1 − Survival Ratecorrected ) (Equation 1) 

The calculation of the test organism survival rate (culturable transmission) was based on the ratio of the 

downstream to upstream culturable organism counts. To remove system bias, the survival rate was 

corrected by the results of the blank no-light transmission test. The blank no-light transmission rate (light 

was not turned on in the test duct) was calculated the same as the survival rate test, but using the 

culturable organism counts from the no-light tests. 

3.5 Average Dose of UV Delivered by the Device 

The equation used to describe the effect of UV on a single species population of airborne microorganisms 

is: 

Nt/N0 = exp(−k · dose) (Equation 2) 

where: 

Nt = the number of microorganisms at time t, 

N0 = the number of microorganisms at the start, 

k = a microorganism-dependent rate constant, in cm2

/μW·s. The k value includes a standard 

deviation because there is not a single microorganism, but a population. 

5
ln (N t N 0 ) (Equation 3)

Dose = −

k 

The fractional inactivation achieved by the device is (1 − Nt/N0), as indicated in Equation 1 and where 

Nt/N0 is the survival rate. 

We calculate the dose by rearranging Equation 2 to yield 

Mean dose was computed from Equation 3 using the values of Nt and N0 obtained with B. atrophaeus and 

using the organism-specific value of k for this organism (1.6 x 10-4 

" 0.3x 10-4 cm2/μW·s). B. atrophaeus 

was selected for determining dose based on earlier RTI measurements. 

The UV dose calculated in this manner is the mean dose to a single organism having an “average” 

trajectory through the device. It is reported here as a characteristic of the device being tested. Dose is 

shown as a mean and a range (mean standard deviation), reflecting the natural variation in a population of 

microorganisms and the spread of the measured values. 

4.0 QUALITY ASSURANCE/QUALITY CONTROL 

4.1 QUALITY ASSURANCE 

Quality assurance/quality control (QA/QC) procedures were performed in accordance with the APCT 

Center and ETV quality management plans (QMPs) and the test/QA plan for this technology. 

(7, 8, 1) 

4.1 Equipment Calibration 

4.1.1 Reference Methods 

As noted in Chapter 1, while reference methods were not available for determining the inactivation 

efficiency of the device, accepted methods developed and used in related work were used. Test 

specifications given in the appendices of the approved test/QA plan were derived from the related 

ASHRAE 52.2 method, with additional specifications and quality control checks relevant to this 

testing.(1,4) 

4.1.2 Instrument Checks 

The DC24-6-120 was installed in the test duct, and operated and maintained according to the vendor’s 

instructions throughout the test. No maintenance was required during the test. The test rig and 

measurement instruments were checked according to the appendices of the approved test/QA plan and 

supplement. 

4.2 Audits 

4.2.1 Performance Evaluation Audit 

No performance evaluation audits were performed during this test. 

6
4.2.2 Technical Systems Audit (TSA) 

No internal or EPA audit was performed during this APCT testing although one is planned for the next 

product to be tested. During RTI's Technology Testing and Evaluation Program (TTEP) which evaluated 

similar UV light systems, both Gene Tatsch9

, then APCT Center quality manager, and Shirley Wasson10, 

then EPA quality manager, performed combined quality system audits (QSAs)/TSAs of RTI’s filter test 

facility. No significant findings were noted in those assessments that might have impacted the quality of 

the TTEP results. Minor recommendations were made and were implemented. The current test is being 

performed using the same equipment and the same methods as during the TTEP testing. 

4.2.3 Data Quality Audit 

At least 10% of the data acquired during the verification testing of the device was audited by Gene Tatsch 

as a representative of the APCT Center quality manager, Cary Eaton. Gene traced the data from the initial 

acquisition, through reduction and statistical analysis, to final reporting, to ensure the integrity of the 

reported results. All calculations performed on the data undergoing the audit were checked. 

4.3 QA/QC Reporting 

Each assessment and audit was documented in accordance with the test/QA plan.(1) Once the assessment 

report was prepared, the RTI task manager ensured that a response was provided as appropriate. For this 

technology evaluation, no significant findings were noted in any assessment or audit, and no follow-up 

corrective action was necessary. The testing followed quality assurance and quality control requirements 

as given in the test/QA plan. The APCT Center quality manager reviewed the test results and the quality 

control data and concluded that the data quality objectives as shown in Table 4-1 were attained. 

Table 4-1. DQOs for Biological Aerosols 

Parameter Frequency and description Control Limits 

Minimum upstream counts 

for samplers 

Each efficiency test. Minimum of 10 CFUa

/plate or PFUb/plate 

Maximum counts for 

samplers 

Each efficiency test. Maximum of 500 CFU/plate or 800 

PFU/plate 

100% Penetration 

(no light) 

(correlation test) 

Performed at least once per test 

sequence per organism. 

Test Acceptable 

Organism Penetration Range 

B. atrophaeus 0.85 to 1.15 

S. marcescens 0.80 to 1.20 

MS2 0.75 to 1.25 

Upstream CFUs Each test. Statistical check of 

data quality. 

CVc # 0.25 

Upstream PFUs Each test. Statistical check of 

data quality. 

CV # 0.35 

a

 CFU = colony forming units 

b

 PFU = plaque forming unit c

 CV = coefficient of variance 

7 
Attribute Measured or Calculated Values 

Test duct operating conditions 

Air flow rate 0.93 m3/sec (1970 cfm) 

Inlet and outlet temperature Upstream 23.1 °Ca (73.6°F) , Downstream 

23.8 °Ca (74.8 °F) 

UV exposure conditions provided by device 

Mean dosage calculated from Equation 3 and range resulting 

from standard deviation of the k value 

23,600 (19,900 – 29,000) μW-s/cm2 

A single irradiance measurement at 254 nm 6290 μW/cm2 at 161 cm (63 in.) upstream 

from the lamps at 0.93 m3/sec (1970 cfm) 

Measures of energy consumption by the unit 

Power consumed by the lamps/ballasts and by any 

 ancillary equipment required by the vendor 

488 W 

Pressure drop across the device < 27.9 Pa (0.112 in. H20) 

Air temperature rise through the device 0.7 °C (1.2 °F)

Data quality objectives (DQOs) are qualitative and quantitative statements designed to ensure that the 

type, quality, and quantity of data used are appropriate for the intended application. In addition, the 

minimum and maximum upstream counts help to ensure that the challenge concentration of each 

organism entering the UV device remains at an acceptably steady value that is sufficiently low such that 

device performance should be independent of the concentration at the test conditions used in this study. 

5.0 TEST RESULTS 

The bioaerosol inactivation efficiency results, derived using Equation 1, are given in Table 5-1. Table 5-2 

provides other information about the UV system. 

Table 5-1. Inactivation Efficiency, % 

Spore form of 

bacteria 

(B. atrophaeus) 

Vegetative bacteria 

(S. marcescens) 

Bacterial virus 

(MS2 bacteriophage) 

Inactivation 

efficiency (UV 

light on), % 

98 ≥ 99.5a

 99 

a – the value 99.5 represents a 95% confidence limit for S. marcescens. There were no downstream counts 

measured. 

Table 5-2. Other Information for the DC24-6-120 

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6.0 LIMITATIONS AND APPLICATIONS 

This verification report addresses the inactivation efficiency performance (Table 5-1) for the American 

Ultraviolet Corporation DC24-6-120 ultra-violet light system that operates in an HVAC system. Other 

measures are given in Table 5-2. Users may wish to consider other performance parameters such as 

service life and cost when selecting a UV light system for their application. 

7.0 REFERENCES 

1. RTI. 2007. Test/QA Plan for Biological and Aerosol Testing of General Ventilation Air Cleaners, and 

Supplement Bioaerosol Inactivation Efficiency by HVAC In-Duct Ultraviolet Light Air Cleaners. 

Research Triangle Institute, Research Triangle Park, NC. 

2. Knight, V. 1973. Viral and Mycoplasmal Infections of the Respiratory Tract, Lea & Febiger, 

Philadelphia, PA. 

3. Buckland, F.E., and Tyrell, D.A.S. 1962. Loss of Infectivity on Drying Various Viruses, Nature 195: 

1063-1064. 

4. ANSI/ASHRAE (American National Standards Institute/American Society of Heating, Refrigerating 

and Air-Conditioning Engineers). 1999. ANSI/ASHRAE Standard 52.2-1999, Method of Testing 

General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size, Section 5.16.2, 

Atlanta, GA. 

5. VanOsdell, D. and K. Foarde. 2002. Final Report ARTI-21CR/610-40030-01 Project – Defining the 

Effectiveness of UV Lamps Installed in Circulating Air Ductwork, Air-Conditioning and 

Refrigeration Technology Institute, 4100 N. Fairfax Drive, Suite 200, Arlington, Virginia 22203. 

http://www.arti-21cr.org/research/completed/finalreports/40030-final.pdf 

6. Adams, M.G. (1959). Bacteriophages. Interscience, New York. 

7. RTI. 2005. Quality Management Plan for Verification Testing of Air Pollution Control Technology, 

Revision 2.2, Research Triangle Park, NC. http://www.epa.gov/etv/pubs/APCT_QMP_0205.pdf 

8. U.S. EPA. 2002. Environmental Technology Verification Program Quality Management Plan, 

EPA/600/R-03/021, U.S. EPA, Cincinnati, OH, 2002. 

http://www.epa.gov/etv/pubs/ETV_02_QMP.pdf 

9. Tatsch, C. Eugene. 2005. Assessment of RTI's TTEP Project, Research Triangle Institute, Research 

Triangle Park, NC. 

10. Wasson, Shirley. 2005. Quality and Technical Systems Audits for Technology Testing and Evaluation 

Program Bioaerosol Inactivation Efficiency by HVAC In-Duct Ultraviolet Light Air Cleaners, US 

EPA, Research Triangle Park, NC. Laura Nessley and David Proffitt from Arcadis G&M participated 

in the audit with Ms. Wasson. 

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