System-Connected Carbon Monoxide Detectors
Detectors SYSTEM SENSOR
The use of early warning carbon monoxide (CO) detectors can result in a significant reduction of CO-related poisonings and deat
system-connected, monitored carbon monoxide detection provides an extra level of protection for building residents or occupants
who cannot appro-
priately respond to a local CO detection alarm. The sooner occupants and authorities are notified of dangerous CO levels in a g
iven environment, the
better the outcome for avoiding serious injury or death. This document provides guidance for the proper operation of system-con
nected CO detectors.
Correct installation and maintenance of CO detectors helps prevent unwanted alarms and ensures proper functioning of devices. T
he latest generation
of CO detectors, when installed and maintained properly, significantly limits the nuisance alarms that initially desensitized o
ccupants when repeated
nuisance alarms occurred in earlier-generation CO detectors. Today’s CO detection devices are effective, trustworthy, and the o
nly means to detect the
odorless, tasteless, and deadly carbon monoxide gas.
Section 1: Standards That Apply
Testing Laboratories ............................................................................................2
Section 2: Carbon Monoxide Overview .............................................................3
What is CO? .........................................................................................................3
How CO Affects the Human Body .....................................................................3
Common Soures of CO .......................................................................................3
Section 3: How Carbon Monoxide Detectors Work ..........................................4
Biomimetic CO Detector Operation ...................................................................4
Metal Oxide Semiconductor CO Detector Operation .......................................4
Electrochemical CO Detector Operation ...........................................................4
Limited Life of System-Connected CO Detectors .............................................4
Section 4: Installation Guidelines
Placement and Spacing
Section 5: Testing, Maintenance, and Service of Detectors ............................7
Typical Inspection, Testing, and Maintenance Practices .................................7 APPLICATIONS GUIDE: SYSTEM-CONNECTED CARBON MONOXIDE DETECTORS
The purpose of this guide is to provide information on the proper appli-
cation of system-connected carbon monoxide (CO) detectors in ordinary
indoor locations (not to meet outdoor EPA or indoor OSHA requirements*).
The guide outlines basic principles and standards that should be consid-
ered in the application of early warning CO detection devices in relation to
the characteristics and effects of CO gas.
Codes and Standards That Apply
International Code Council (ICC)
The ICC publishes numerous codes used to construct all residential
dwellings and commercial buildings. A code specifies WHEN, what type
of CO detection is required and the location of CO detectors.
National Fire Protection Association (NFPA)
Quincy, MA 02269-9101
NFPA publishes standards for the proper application, installation, and main-
tenance of CO detection. NFPA 720-2015 is the
Standard for the Installation
of Carbon Monoxide (CO) Detection and Warning Equipment
. A standard
specifies HOW carbon monoxide detection and warning equipment is to
be installed, tested, maintained and monitored.
is primarily concerned with life safety, not with protection of
covers the selection, design, application, installation, loca-
tion, performance, inspection, testing, and maintenance of CO detection
and warning equipment in buildings and structures.
contains requirements for the selection, installation, opera-
tion, and maintenance of equipment that detects concentrations of CO that
could pose a life safety risk to most occupants in buildings and structures.
Highlights of the new standards, which should be reviewed in their entirety
before specifying or installing CO detectors, follow. NFPA 720-2015:
Nationally standardizes CO detection for all buildings, not just res-
idences. This includes schools, hotels, nursing homes, apartment
buildings and other commercial structures.
Requires CO alarm signals to be distinct and “descriptively annunciated”
from fire alarm, CO supervisory, and CO trouble signals. Furthermore,
the CO alarm signal should take precedence over supervisory or trou-
ble signals. CO detector trouble signals must be indicated visually and
audibly at the control panel and supervising station. Therefore, the CO
detector must have a means to signal the panel upon trouble condi-
tions. For example, hardwired detectors require an integral trouble relay
to send the trouble signal to the panel.
Now holds CO detectors to the same life safety standard as smoke
detectors: They will send trouble signals to the control panel and facili-
tate wiring supervision.
Defines CO detector location more specifically than ever. In commer-
cial buildings, CO detectors need to be located on the ceiling in the
same room as permanently installed fuel-burning appliances. They also
need to be centrally located on every habitable level and in every HVAC
zone of the building. In dwelling units, CO detectors must be installed
outside each separate sleeping area and on every level of a dwelling
unit, including basements. Applicable laws, codes, and standards may
require additional locations.
Requires CO detection systems to have sufficient secondary power to
operate the system under quiescent load (system operating in normal
condition) for at least 24 hours. After that time, the system must operate
all of the CO notification appliances for 12 hours if a supervising station
does not monitor the system. If monitored by a supervising station, the
12-hour requirement can be reduced to 5 minutes.
Includes CO detector testing requirements. However, the requirement to
be able to functionally test the CO detector in a manner similar to test-
ing smoke detectors with canned smoke. Note that the System Sensor
CO1224T with RealTest
meets this testing requirement.
CO detectors shall be replaced when the end-of-life signal is
activated, the manufacturer’s replacement date is reached, or when they
fail to respond to operability tests.
Clarifies what supervising stations should do when they receive a CO
alarm signal. If the communications methodology is shared with any
other usage, all fire alarm, CO alarm, supervisory, and trouble signals
will take priority, in that order of priority, over all other signals unless oth-
erwise permitted by the AHJ.
The integral sounder of a CO detector may be sufficient for notifying
occupants of commercial and residential buildings. It allows occupant
notification to be limited to the notification zone encompassing the area
where the CO signal is originated, if the CO alarm signal is transmitted
to a constantly attended onsite location or off-premises location.
Testing laboratories test smoke detectors, CO detectors, control panels,
and other components of fire alarm systems to verify conformance with
NFPA requirements and their own standards. Equipment that passes their
tests is identified by a label and/or listing.
Underwriters Laboratories, Inc. (UL)
Northbrook, IL 60062
455 E. Trimble Road
San Jose, CA 95131
1285 Walt Whitman Road
Melville, NY 11747
12 Laboratory Drive, P.O. Box 13995
Research Triangle Park, NC
2600 N.W. Lake Road
Camas, WA 98607
National Fire Protection Association (NFPA). “NFPA 720: Standard for the Installation of Carbon Monoxide (CO) Detection and War
Document Scope.” NFPA.org. http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=720&cookie_test=1#.
* See page 7 for information on CO for worker safety. SYSTEM SENSOR
The following UL standards apply to CO detectors:
is the product standard for CO detectors connected to a con-
trol panel via conductors or low-power radio frequency (wireless).
is the product standard that covers self-contained CO alarms
that are not designed or listed to be connected to a control panel.
It is important to note that the alarm thresholds of UL 2034 CO alarms and
UL 2075 CO detectors are the same. Section 15.1 (b) of UL 2075 requires
detectors to operate within the sensitivity parameters defined by UL 2034.
Table 38.1 of UL 2034 defines the actual alarm thresholds, which are:
– 30 ppm no less than 30 days
– 70 ppm 60 to 240 minutes
– 150 ppm 10 to 50 minutes
– 400 ppm 4 to 15 minutes
Carbon Monoxide Overview
Carbon monoxide (CO) is an odorless, tasteless and highly toxic gas that
results from the incomplete combustion of fossil fuels. It is often referred
to as “the silent killer” because it is virtually impossible to detect without
sensing technology. On average, from 2004 to 2006, over 20,000 people
per year visited emergency rooms after accidental, non-fatal CO expo-
sures.2 From 1999 to 2004, an average of 439 people died from accidental
What is CO?
The CO molecule is made up of a carbon and an oxygen atom. CO has a
density similar to air, but typically rises from the point of production due to
the heat of combustion. As it cools to environmental temperatures, how-
ever, it circulates in the same manner as ambient air.
How CO Affects the Human Body
Through the normal process of respiration and circulation, oxygen mole-
cules enter the lungs and are transported to cells throughout the body by
attaching to hemoglobin in the blood. CO molecules, however, attach to
hemoglobin far more readily than oxygen. When CO is present in the envi-
ronment, these molecules interfere with the normal circulation of oxygen
throughout the body by attaching to hemoglobin that would normally trans-
port oxygen. (See Figure 1.) This can cause varying levels of injury and
sickness, depending on length and level of exposure.
CO poisoning can result from prolonged exposure to low levels of CO or
shorter exposures to higher concentrations. Table 1 shows the relationship
between CO volume, length of exposure, and resulting symptoms to a per-
son within a given environment.
Common Sources of CO
CO is formed from the incomplete combustion of fossil fuels. The oper-
ation of many common appliances, machinery, and heating equipment,
if not working or vented properly, can result in dangerous CO build-up
in a given environment. According to recent studies, the primary sourc-
es for CO fatalities are:
– Heating systems
– Power tools
– Charcoal grills or other charcoal sources
– Gas ranges or ovens
– Camp stoves or lanterns
– Other or multiple appliances
From 2004 to 2006, the top two sources for non-fatal, accidental CO expo-
sures in the U.S. were home heating systems (16.4 percent) and motor
vehicles (8.1 percent).
Other common sources of CO in and around the
– Stove/gas ranges
– Gas line leaks
– Gas water heaters
– Blocked or clogged chimneys
– Gas or wood burning fireplaces
– Cracked heat exchangers
– Leaking, cracked, corroded, or disconnected flue or vent pipes
– Barbecue grills operated in enclosed areas, such as a garage
– Unvented gas space heaters
2. CDC. Unintentional non-fire-related carbon monoxide exposures in the United States, 2004-2006. MMWR 2008;57:896-899.
3. CDC. Carbon Monoxide-Related Deaths — United States, 1999-2004. MMWR 2007;56:1309-1312.
NFPA 720, 2012 edition, Annex B Dangers of Carbon Monoxide, B.1 Carbon Monoxide, Table B.1 Symptoms of Carbon Monoxide Exposure
Carbon Monoxide (CO)
Figure 1. Carbon monoxide in the bloodstream APPLICATIONS GUIDE: SYSTEM-CONNECTED CARBON MONOXIDE DETECTORS
How Carbon Monoxide
Carbon Monoxide (CO) detectors are devices that monitor the amount of
CO in the air over a given time period. Distinguished by their sensing tech-
nology, three basic types of CO detectors are used today: biomimetic, metal
oxide semiconductor, and electrochemical.
Biomimetic CO Detector Operation
Biomimetic CO detectors mimic how hemoglobin in biological organisms
reacts to CO. Specifically, a biomimetic sensor monitors infrared light that
is passed through a disc of synthetic hemoglobin that darkens in the pres-
ence of CO. Thus, as CO concentrations increase, the light is obscured,
triggering the alarm.
– Low cost
– High false alarm rate
– Long recovery after
– Long life span
– High current draw
to chemicals and gases
other than CO
– Reliable, few field
High sensitivity to ammo-
Table 2. Comparison of carbon monoxide detection technologies
Biomimetic detectors are low cost and require a low current draw to
operate. However, these detectors are susceptible to false alarms if envi-
ronmental conditions fluctuate outside peak operating ranges. Other types
of sensors are much more reliable. Furthermore, biomimetic sensors have
a shorter life than other types of CO sensors and they require a long recov-
ery time after alarm.
Metal Oxide Semiconductor CO Detector Operation
With metal oxide semiconductor (MOS) detector technology, a tin dioxide
semiconductor is heated by an electric current at periodic intervals. When
tin dioxide reaches its operating temperature, it is capable of changing
its resistance in the presence of carbon monoxide. Once the resistance
change reaches its threshold, an alarm sounds.
MOS detectors have a long life span and can respond quickly to CO.
However, they are more expensive to purchase and operate than other
types of sensors. Because it uses an electrical current to heat the semi-
conductor, this type of sensor requires a high current draw. Furthermore,
MOS detectors are susceptible to false alarms in the presence of some
common household chemicals or gases other than CO.
Electrochemical CO Detector Operation
Electrochemical sensors use a platinum electrode and acid combination
to promote a reaction between CO and the oxygen in the air, which then
produces an electric current. When CO is present in the air over time, if
the current increases beyond specific thresholds, the alarm is sounded.
CO detectors using electrochemical sensors have been in use in indus-
trial applications for many years. These detectors are reliable, with few field
defects, have a low current draw, and respond quickly to CO. However, they
may be susceptible to false alarm in the presence of household cleaners
that contain ammonia, such as glass cleaners.
The life of the electrochemical sensor is typically longer than that of bio-
mimetic sensors. All CO detectors need to be replaced at the end of their
Limited Life of System-Connected CO Detectors
All system-connected CO detectors on the market have a limited-life gas
sensor and UL requires that CO detectors be replaced at the end of that
component’s life. Therefore, it is imperative that the gas sensor be super-
vised in order to avoid an undetected inoperable detector, which is a
fundamental function of all fire alarm system devices and Central Station
UL and NFPA 720 require every system-connected CO detec-
tor to provide a means to send the sensor’s end-of-life signal to the
control panel. To aid in ongoing maintenance and to ensure CO detec-
tors are providing promised protection, it is highly recommended that
you purchase CO detectors with an end-of-life signal.
Figure 2. Cutaway view of an electrochemical CO sensor cell
CO Concentration in
Parts Per Million (PPM)
No adverse effects with 8 hours of exposure
Headache, nausea, and dizziness after
45 minutes of exposure; collapse and
unconsciousness after 2 hours of exposure
Loss of consciousness after 1 hour of exposure
Headache and dizziness after 1-2 minutes of
exposure; unconsciousness and danger of
death after 10-15 minutes of exposure
Table 1. Symptoms of carbon monoxide exposure
4 SYSTEM SENSOR
When installing a carbon monoxide (CO) detector, do not install it in any
environment that does not comply with the detector’s environmental spec-
ifications. All CO detectors should be installed in accordance with NFPA
720-2015 — the
Standard for the Installation of CO Detection and Warning
— which defines standards for both commercial and residen-
tial installations of CO detectors.
2015 Edition of the IRC
The 2015 edition of the International Residential Code (IRC), CO detectors
are required in dwelling units shall be installed outside of each separate
sleeping area in the immediate vicinity of the bedrooms that have a perma-
nently installed fuel-burning appliance or an attached garage. Where the
fuel burning appliance is located within a bedroom or its attached bath-
room, a CO detector shall be installed within the bedroom.
2015 Edition of IFC/IBC
For the 2015 edition of the IFC/IBC, CO detection is now required in “sleep-
ing rooms” of newly constructed hotels, apartment buildings, dormitories,
hospitals, nursing homes, in classrooms of kindergarten through grade
12 (K-12) schools that have a permanently installed fuel-burning appli-
ance or an attached garage. An open parking garage, as defined in the
International Building Code, or enclosed parking garage ventilated in
accordance with Section 404 of the International Mechanical Code shall
not be deemed to be an attached garage.
For buildings that have a fuel-burning HVAC system, the IFC/IBC requires
CO detection in each dwelling unit, sleeping unit or classroom that is
served by forced air furnace. However the requirement provides the system
designer with the latitude of not installing CO detection in these locations if
CO detection provided in the first room or area served by each main duct
leaving the furnace, and the CO alarm signal is automatically transmitted to
an approved location. If the FBA is located outside a dwelling unit, sleep-
ing unit or classroom, CO detection is then required to be installed on the
ceiling of a room containing a FBA or in an approved location between the
room containing the FBA and the dwelling unit, sleeping unit or classroom.
2015 Edition of NFPA 101
For the 2015 edition of NFPA 101, CO detection is required outside sleeping
units in one- and two-family dwellings, rooming houses, hotels, dormitories
apartment buildings, and kindergarten through grade 12 (K-12) schools.
CO detection is required in these occupancies when they contain a perma-
nently installed fuel-burning appliance or when they have a communicating
attached garage. An open parking garage, as defined in the Building Code,
or enclosed parking garage ventilated in accordance with Mechanical
Code shall not be deemed to be an attached garage. In addition to the
sleeping area requirements, CO alarms or detectors are required to be
installed in the following non-sleeping locations in hotels, dormitories and
apartment buildings. First, on the ceiling in rooms containing a permanently
installed fuel-burning appliance. The second requirement is for detection
to be centrally located within occupiable spaces served by the first sup-
ply air register from a fuel-burning HVAC system.
Placement and Spacing
The following provides general guidelines for CO detector placement and
spacing. Always follow manufacturer instructions regarding placement and
spacing of your particular CO detector.
When wall mounting a system-connected CO detector, it should be at least
as high as a light switch, and at least six inches from the ceiling. The detec-
tor should not be mounted near the floor. As noted in “Section 2: Carbon
Monoxide Overview,” CO gas typically rises from the point of production
and then mixes evenly throughout the air as it cools. Furthermore, higher
placement protects the detector from potential damage caused by pets
and tampering by small children.
When ceiling mounting a system-connected CO detector, the detector
should be located at least 12 inches from any wall. APPLICATIONS GUIDE: SYSTEM-CONNECTED CARBON MONOXIDE DETECTORS
Testing, Maintenance, and Service of Detectors
Carbon monoxide (CO) detectors are designed to be as maintenance free
as possible; however, dust, dirt, and other foreign matter can accumu-
late inside a detector’s sensing elements and change its sensitivity. They
can become either more sensitive, which may cause unwanted alarms, or
less sensitive, which could reduce the amount of warning time given if CO
reaches a dangerous level. Furthermore, as discussed in “Section 3: How
Carbon Monoxide Detectors Work,” the sensing cell of CO detectors have
a limited life span. Therefore, detectors should be tested periodically and
maintained at regular intervals. Always follow the manufacturer’s specific
recommended practices for maintenance and testing. Also refer to NFPA
720-2015, sections 1.1.2 and 1.1.3.
Carbon monoxide detectors are sophisticated electronic devices that
need periodic testing and maintenance. To maintain the integrity of any
CO alarm system, it is important to have a qualified person periodically
test the system.
Typical Inspection, Testing, and Maintenance Practices
It is recommended that a CO detector should be inspected visually and the
functionality tested by the introduction of carbon monoxide into the sensing
chamber immediately after installation and annually thereafter. This ensures
that each detector remains in good physical condition and that there are no
changes that would affect detector performance, such as building modifi-
cations, occupancy hazards, and environmental effects.
Notify the proper authorities that the CO detector is undergoing main-
tenance to avoid nuisance alarms and to prevent unwanted alarms and
possible dispatch of emergency services. Next, make sure the detector’s
gas entry ports are not clogged. Follow the manufacturer’s instructions to
test the mechanical functioning of the detector. Typically, CO detectors
come with a “Test” button for this purpose. Finally, perform a functional
test of the CO detector’s CO sensing cell (see “Future Testing Guidelines”
below) if the detector has this capability. Again, refer to the manufacturer’s
recommended procedure for performing this test.
Once testing and maintenance is completed, restore the zone or system.
Notify the proper authorities that testing has been completed and the sys-
tem is again under normal operation.
CO for Worker Safety
In accordance with section 5.2.1* of NFPA 720, Standard for the Installation
of Carbon Monoxide (CO) Detection and Warning Equipment, the products
and systems covered in the standard are intended for the protection of life.
CO detection to monitor air quality for public health or worker safety is not
addressed in NFPA 720. Typical systems intended for monitor air quality for
worker safety are underground or enclosed garages where the CO detec-
tion levels are lower than those addressed by NFPA 720.
The alarm threshold for parking structures, loading docks and automotive
repair garages are considered to monitor the air quality for worker safety
are determined by several governmental organizations:
– Occupational Safety and Health Administration (OSHA)
– The National Institute for Occupational Safety and Health (NIOSH).
The OSHA permissible CO exposure limit is 50ppm for 8 hours and the
NIOSH permissible CO exposure limit is 35 ppm for 8 hours and 200ppm
as a ceiling. The OSHA, and NIOSH requirements can be found at:
tion.html SYSTEM SENSOR
©2016 System Sensor. The company reserves the right to change specifications at any time.
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