ISO 15714:2019

Method of evaluating the UV dose to airborne microorganisms transiting in-duct ultraviolet germicidal irradiation devices

This document describes a method in laboratory to assess the performance of ultraviolet germicidal irradiation (UVGI) devices which will be mounted in-duct in heating, ventilating and air-conditioning (HVAC) systems. The method includes the detailed requirements for test rig, microorganisms, procedures, data calculation and result report to determine the UV dose to model microorganisms by an UVGI device at several airflow rates. By the testing results, the capacity of in-duct UVGI devices for air disinfection can be evaluated and compared reliably. If the susceptibility constant of a given microorganism is known, the inactivation rate of that micro-organism by the tested UVGI devices can be further calculated.

Méthode d'évaluation de la dose d'UV pour les microorganismes en suspension dans l'air transitant par des dispositifs d'irradiation germicide aux ultraviolets raccordés

General Information

• Status: Published
• Publication Date: 11-Jul-2019
• ICS: 91.140.30 - Ventilation and air-conditioning systems
• Technical Committee: ISO/TC 142 - Cleaning equipment for air and other gases
• Drafting Committee: ISO/TC 142/WG 2 - UV-C technology
• Current Stage: 6060 - International Standard published
• Due Date: 03-Feb-2020
• Completion Date: 12-Jul-2019

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 15714
First edition
2019-07
Method of evaluating the UV dose to
airborne microorganisms transiting
in-duct ultraviolet germicidal
irradiation devices
Méthode d'évaluation de la dose d'UV pour les microorganismes
en suspension dans l'air transitant par des dispositifs d'irradiation
germicide aux ultraviolets raccordés
Reference number
ISO 15714:2019(E)
©
ISO 2019

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ISO 15714:2019(E)

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© ISO 2019
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ISO 15714:2019(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions, symbols and abbreviated terms . 1
3.1 Terms and definitions . 1
3.2 Symbols and abbreviated terms. 3
3.2.1 Symbols . 3
3.2.2 Abbreviated terms . 3
4 Configuration of the test rig . 4
5 Test rig qualification . 5
6 Preparation of test microorganisms . 5
6.1 Test microorganisms . 5
6.1.1 Serratia marcescens . 5
6.1.2 Bacillus subtilis . 5
6.1.3 Cladosporium sphaerospermum . 5
6.2 Preparation of microbial suspensions . 6
6.2.1 Acquisition of pure culture of test microorganisms . 6
6.2.2 Cultivation and dispersion of the test microorganism . 6
6.2.3 Dilution of the microbial suspensions . 6
7 Testing procedure for an in-duct UVGI device . 6
7.1 Determination of airflow rate, temperature and humidity . 6
7.2 Production of the airborne test microorganism . 6
7.3 Measurement of the test microorganism concentration without and with UV irradiation . 7
7.3.1 Sampling procedure . 7
7.3.2 Test microorganism sampling methods . . 7
7.3.3 Test microorganism culture and enumeration . 7
7.4 Repeating the tests at other flow rates . 7
7.5 Determination of the UV susceptibility of the test microorganism . 7
8 Safety and environmental considerations . 7
9 Calculation, evaluation and reporting . 8
9.1 Determination of the inactivation rate of the test microorganism . 8
9.2 Determination of the UV dose of the UVGI device . 8
9.3 Evaluation of the UVGI capacity . 8
9.4 Results reporting . 8
Annex A (informative) Recipe of culture medium for the test microorganism .9
Annex B (informative) Method for determining the UV dose-response curve and
susceptibility constant of a test microorganism in air .10
Annex C (informative) Susceptibility constants of some typical microorganisms in air
by the literature .13
Bibliography .16
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ISO 15714:2019(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso
.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 142, Cleaning equipment for air and
other gases.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
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ISO 15714:2019(E)

Introduction
Airborne microorganisms including some pathogens in indoor air may cause different types of
diseases or adverse health effects on humans. Among different air disinfection techniques, ultraviolet
germicidal irradiation (UVGI) has been used for several decades to effectively inactivate the airborne
microorganisms in indoor air and thereby prevent the transmission of a variety of airborne infections.
In-duct UVGI device is a primary form of air disinfection method by UV lamps mounted in heating,
ventilation and air-conditioning (HVAC) systems to irradiate the microorganisms in air with high
intensities. However, other than the power supply, there is no standard or index available to characterize
or understand the performance of the UVGI products made by different manufacturers. In addition,
effective parameters derived from a standard method are lacking to predict the performance of the
UVGI device on microorganism inactivation in a real HVAC system.
As microorganisms in air are irradiated by UV-C light emitted by an in-duct UVGI device, the
inactivation rate of a specific microorganism primarily depends on the UV dose given by the device
and the susceptibility of that microorganism. If the UV dose under a specific condition is known, the
inactivation capacity and disinfection performance of the UVGI devices can be compared. Furthermore,
the inactivation rate for specific microorganism can be calculated with its susceptibility data known.
Therefore, the development of a standard method to evaluate the UV dose of the in-duct UVGI device is
very useful and necessary.
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INTERNATIONAL STANDARD ISO 15714:2019(E)
Method of evaluating the UV dose to airborne
microorganisms transiting in-duct ultraviolet germicidal
irradiation devices
1 Scope
This document describes a method in laboratory to assess the performance of ultraviolet germicidal
irradiation (UVGI) devices which will be mounted in-duct in heating, ventilating and air-conditioning
(HVAC) systems.
The method includes the detailed requirements for test rig, microorganisms, procedures, data
calculation and result report to determine the UV dose to model microorganisms by an UVGI device at
several airflow rates. By the testing results, the capacity of in-duct UVGI devices for air disinfection can
be evaluated and compared reliably.
If the susceptibility constant of a given microorganism is known, the inactivation rate of that micro-
organism by the tested UVGI devices can be further calculated.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 15858, UV-C Devices — Safety information — Permissible human exposure
3 Terms, definitions, symbols and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at http: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1.1
airborne microorganism
microbial particle with an aerodynamic diameter up to 100 μm suspended in air
Note 1 to entry: Airborne microorganism includes bacterium, fungus, their spore or virus.
3.1.2
pathogen
infectious agent that causes diseases in its host
Note 1 to entry: Pathogen includes some virus, bacterium, prion, fungus, viroid, or parasite.
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ISO 15714:2019(E)

3.1.3
test microorganism
microbial surrogate representing the typical pathogen (3.1.2)
Note 1 to entry: Test microorganism is chosen to be safer than the real pathogen in order to prevent the infection
of testers or analysts.
3.1.4
air disinfection
process that can remove, inactivate or destroy the airborne microorganisms (3.1.1), especially pathogen
(3.1.2) in air
3.1.5
ultraviolet germicidal irradiation
UVGI
method for disinfection of air, water and object surfaces that uses radiation with wavelength in the
range of 240 nm to 280 nm to kill or inactivate microorganism
Note 1 to entry: UV irradiation with a wavelength of 240 nm to 280 nm can cause damage to the DNA or RNA of
the microorganisms.
[SOURCE: ISO 29464:2017, 3.6.20, modified — Note 1 to entry has been added.]
3.1.6
in-duct UVGI device
device consisting of UV lamps, ballast and other accessories, all of which could be mounted in ducts of
an HVAC system to disinfect the air or a surface
Note 1 to entry: A typical diagram of in-duct UVGI device in an HVAC system is shown in Figure 1.
Key
1 filter
2 UV lamp
3 heating or cooling coil
4 fresh air
5 conditioned air
Figure 1 — Diagram of an in-duct UVGI device in an HVAC system
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ISO 15714:2019(E)

3.1.7
UV dose
D
product of UV irradiance and specific exposure time on a given microorganism or surface
2
Note 1 to entry: UV dose is expressed in millijoules per square centimetre (mJ/cm ).
Note 2 to entry: The longer the time a microbe is exposed to UV light, the higher the UV dose it will receive. In a
UVGI air disinfection (3.1.4) device, the UV dose to every single microbe is different. For the device with evenly
distributed UV irradiation and airflow, the UV dose can be calculated based on the definition. But for most real
in-duct UVGI devices (3.1.6), it is hard to evaluate the UV dose to each microbe but the average UV dose can be
determined by the inactivation rate (3.1.9) and a known microbial susceptibility.
3.1.8
UV susceptibility
extent to which a microorganism is sensitive to UV light or how easily it can be inactivated by UV
irradiation
Note 1 to entry: UV susceptibility depends on the species and character of the microorganism. It can be described
2
by a constant (k) with the unit of m /J.
3.1.9
inactivation rate
reduction in active microorganism concentration expressed as N /N (%) or log(N /N), in which N is
0 0 0
the original active microorganism concentration, N is the active microorganism concentration after
disinfection
3.1.10
UV dose-response curve
quantified relationship between the inactivation rate (3.1.9) of a specific microorganism and the
average UV dose (3.1.7) it received
Note 1 to entry: In many cases, the relationship follows the equation as below:
ln(N /N) = k D (1)
0
in which D, k and ln(N /N) have been described in 3.1.7 to 3.1.9. In Formula (1), N/N or D can be calculated with
0 0
the other parameters known. In other cases, the relationship may not strictly follow Formula (1), but N/N or D
0
can also be determined according to the specific curve.
3.2 Symbols and abbreviated terms
3.2.1 Symbols
Symbol Definition
N original active microorganism concentration
0
N active microorganism concentration after disinfection
D UV dose
k susceptibility constant
3.2.2 Abbreviated terms
ATCC American Type Culture Collection
BMBL Biosafety in Microbiological and Biomedical Laboratories
BSL biosafety level
CDC Centres for Disease Control and Prevention of the United States
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ISO 15714:2019(E)

CFU colony-forming unit
HEPA high-efficiency particulate air
HVAC heating, ventilating and air-conditioning
PDA potato dextrose agar
UVGI ultraviolet germicidal irradiation
4 Configuration of the test rig
4.1 In order to evaluate the disinfection capacity of an in-duct UVGI device, the inactivation performance
for some specific test microorganism shall be measured through a standard test rig as shown in Figure 2.
Dimensions in millimetres
Key
1 air 7 downstream duct
2 blower 8 HEPA filter
3 damper 9 injection of test microorganisms
4 HEPA filter 10 UV irradiation
5 upstream duct 11 sampling port for microorganism detection and the
measurement of airflow, temperature and humidity
6 UVGI device mounting duct
Figure 2 — Test rig for inactivation performance of in-duct UVGI device
4.2 The test rig includes a blower (installed in front or at the end of the test rig), a damper, a HEPA
filter before the duct, an upstream duct with test microorganism injection port, a UVGI device mounting
duct, a downstream duct with sampling port and an off-gas pipe with HEPA filter.
4.3 The ducts have a square cross-section and an inner side-length of 0,6 m. Galvanized steel or
aluminium with a reflectivity of 50 % to 60 % shall be used to make the duct walls. The upstream duct
and downstream duct have a length of 2,0 m and the UVGI device mounting duct has a length of 1,0 m.
4.4 In the test rig, a damper is used to control the flow rate of the test system. A subsequent HEPA
filter shall be placed before the test microorganism injection port in order to remove the culturable
microorganisms that may exist in the air to avoid their impact on test microorganism quantification.
4.5 In the upstream duct, a test microorganism injection port of 10 mm to 15 mm in diameter is set
near the left flange of the duct (within 20 cm). The port can be set in the centre line of bottom or side wall.
4.6 In the UVGI device mounting duct, the UVGI device shall be installed following the instruction of
the manufacturer and simulating its working conditions. If a new UV lamp is used, it shall be powered on
continuously for 100 hours (called burn-in time) before it is tested.
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ISO 15714:2019(E)

4.7 In the downstream duct, a sampling port (Key 11 in Figure 2) of 15 mm to 20 mm in diameter is
placed to collect the test microorganisms and to do measurements on the airflow rate, temperature and
humidity by different sensors. The port can be set in the centre line of the bottom or side wall. Connected
with the downstream duct, another HEPA filter is recommended to be installed to minimize the test
microorganism emission to the environment.
5 Test rig qualification
Before launching the testing procedures, the test rig needs to be examined to insure that it is in a good
condition and can provide reliable results. The methods for test rig qualification shown in Section 5
of ANSI/ASHRAE 185.1 are a useful reference. Tests on the velocity uniformity and duct leakage are
recommended. All the qualification tests shall be operated at an air velocity of (2,0 ± 0,2) m/s.
6 Preparation of test microorganisms
6.1 Test microorganisms
6.1.1 Serratia marcescens
Serratia marcescens is a species of rod-shaped Gram-negative bacteria in the family Enterobacteriaceae.
They are frequently used as typical test microorganisms for biodosimetry purposes and are good
surrogates of those bacteria with high susceptibility to UV, especially many Gram-negative bacteria.
2 2
The reported susceptibility constants (k) for Serratia marcescens range in 0,1 m /J to 0,9 m /J. The
recommended culturing media are nutrient agar (solid) which are commercially available and easy to
prepare (the recipe is listed in Annex A).
2
Serratia marcescens is suitable for testing the UVGI device with an effective UV dose less than 25 J/m .
6.1.2 Bacillus subtilis
Bacillus subtilis is a species of rod-shaped, Gram-positive and endospore-forming bacteria in the family
Bacillaceae. They are frequently used as typical test microorganisms representing those bacteria with
low susceptibility to UV, especially the Gram-positive bacteria. The reported susceptibility constants
2 2
(k) for Bacillus subtilis (vegetative cells) range in 0,02 m /J to 0,07 m /J. The recommended culturing
media are nutrient agar (solid) which are commercially available and easy to prepare (the recipe is
listed in Annex A).
2 2
Bacillus subtilis is suitable for testing the UVGI device with an effective UV dose from 25 J/m to 120 J/m .
6.1.3 Cladosporium sphaerospermum
Cladosporium sphaerospermum is a saprobic and spore-forming fungus that inhabits a variety of
environments including the indoor and outdoor air. They are typical test microorganisms representing
those fungi with very high susceptibility to UV. The reported susceptibility constants (k) for
2 2
Cladosporium sphaerospermum spores in single-pass tests range in 0,000 8 m /J to 0,002 m /J. The
recommended culturing media are potato dextrose agar (PDA) (solid) which are commercially available
and easy to prepare (the recipe is listed in Annex A).
Cladosporium sphaerospermum is suitable for testing the UVGI device with an effective UV dose more
2
than 120 J/m .
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ISO 15714:2019(E)

6.2 Preparation of microbial suspensions
6.2.1 Acquisition of pure culture of test microorganisms
All the test microorganisms above are available for purchase through some national or global biological
resource centres like American Type Culture Collection (ATCC) and have a biosafety level of 1 (not
known to consistently cause disease in healthy adult humans) classified by the Centres for Disease
Control and Prevention of the United States (CDC).
6.2.2 Cultivation and dispersion of the test microorganism
Inoculate the test organism onto solid media as indicated in the previous section, incubating the culture
until mature, wiping a wetted sterile swab across the surface of the pure culture, and eluting from the
swab into sterile deionized water to obtain a 600 nm absorbance of 0,8 to 1,0 with a 1 cm cuvette.
6.2.3 Dilution of the microbial suspensions
Dilute the microbial suspension to achieve a suitable test microorganism concentration typically
4 3 8 3
ranging in 10 CFU/cm to 10 CFU/cm . The exact concentration shall meet the requirement for
producing an air stream with a desired concentration.
7 Testing procedure for an in-duct UVGI device
7.1 Determination of airflow rate, temperature and humidity
The performance of an in-duct UVGI device can be affected by airflow rate, temperature, humidity and
other factors. Among these impacting factors, airflow rate is the most important one and a reasonable
range shall be determined before the test. Adjust the airflow rate to the desired level by selecting a
3
suitable blower and changing the angle of the damper. Three airflow rates at (1 000 ± 100) m /h,
3 3
(2 000 ± 100) m /h and (3 000 ± 100) m /h shall be selected for the inactivation test.
Air temperature and relative humidity are less important than the airflow rate but still need to
be controlled within (25 ± 2,5) °C and 50 % ± 10 % during the testing period. The exact level of air
temperature and humidity with the UV irradiation switched on shall be noted as a reference condition
while demonstrating the testing results.
At the sampling port in downstream duct indicated in Figure 2 (Key 11), the airflow rate shall
be measured by a portable anemometer (with a relative accuracy better than ±10 %) and the air
temperature and humidity shall be measured by a digital hygrometer (with absolute accuracies better
than ±0,5 °C for temperature and ±3 % for relative humidity). The measurements of airflow rate,
temperature and humidity shall be repeated twice and the relative difference in the same index shall be
less than 10 % to ensure the testing system is stable.
All the three parameters shall be tested at the beginning and end of each test. The relative variations
shall be less than 10 %.
7.2 Production of the airborne test microorganism
The test microorganism with desired concentrations can be generated by a Collison nebulizer or
ultrasonic air humidifier with fans and shall be injected into the airstream via a tube. Refer to 4.5
for the injection position. By adjusting the test microorganism concentration in suspensions and the
setting of the generator, the microbe concentration in the air stream can be controlled. The suitable
3 3 4 3
range shall be 10 CFU/m to 10 CFU/m .
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ISO 15714:2019(E)

7.3 Measurement of the test microorganism concentration without and with UV
irradiation
7.3.1 Sampling procedure
After the test microorganism concentration is adjusted to the desired level, the airborne microorganism
shall be sampled with UVGI switched off at the sampling port in the downstream duct (Key 11 in
Figure 2). The airborne microorganism concentration with UVGI switched off functions as a control
to avoid the effect of air duct on microbe inactivation. After the sampling with UVGI switched off are
completed, turn on the UV lamp and preheat it for 15 min. Then do the test microorganism sampling
with UVGI on at the same sampling port with the same methodology.
7.3.2 Test microorganism sampling methods
The sampling of the test microorganism can be accomplished by an impaction type air sampler such
as Andersen sampler or a commercial impinger. The device and procedure for all sampling shall
be identical throughout the test. The sampling shall be repeated three times and at least two tested
concentrations shall have a relative difference less than 50 %.
7.3.3 Test microorganism culture and enumeration
After agar plates are taken out of the impaction type air sampler or the suspension sample from an
impinger is spread on agar plates, put them directly into an incubator at 32 °C for bacteria for 24 h
to 48 h and 25 °C for fungi for 72 h to 120 h after which the number of colonies is counted. Then the
airborne microorganism concentration can be calculated as the number of colonies in a certain volume
3
of air (CFU/m ) considering the sampling flow rate and time. All the results with less than 50 % relative
difference between any two of them shall then be averaged to do the performance calculation.
7.4 Repeating the tests at other flow rates
After completing the steps described above, the UVGI device can be turned off and a new airflow rate
can be set to repeat the testing procedure from 7.1 to 7.3. All the tests under each designated flow rate
shall be completed. If some mistakes are found or some results do not meet the requirements, some
steps or measurement shall be repeated.
7.5 Determination of the UV susceptibility of the test microorganism
The UV susceptibility (UV dose-response curve) of the test microorganism shall be tested for calculating
the UV dose of the UVGI device. The detailed method is described in Annex B. Note that the exact same
test microorganism, its generation and testing methods shall be used. Besides, all the other conditions
such as air temperature, humidity and initial microbe concentration shall also be kept at the same level.
If the UV susceptibility test is not available, the citation of UV susceptibility constant is also acceptable
(see Annex C) with the value and reference noted in the report.
8 Safety and environmental considerations
8.1 During the test, the first safety concern is the possible personal exposure to UV. The operation
of the UVGI device shall follow ISO 15
...