Why CO Detector Choice Is Critical

Increasingly, states and local jurisdictions are mandating the installation of carbon monoxide (CO) detectors. Alarm professionals therefore must not only comply with the industry’s most recent product standards, but understand the differences among various new requirements.

Because the current gas sensing technologies on the market – biomimetic, metal oxide semiconductor (MOS) and electrochemical – all have a limited life, it is imperative the gas sensing element be supervised to ensure continuous operation. The new requirements of the third edition of ANSI/UL 2075 address this issue by mandating critical life-safety supervision features that will prevent a failed detector from going undetected.

These new requirements are fundamental concepts of all life-safety products, such as fire alarm system devices and central station service.

The new ANSI/UL 2075 requires the detector to electrically supervise the gas sensing element so when the sensor reaches its end-of-life (EOL), the detector will send a trouble signal to the control panel. This new electrical supervision requirement of the CO sensing element is vital for safe and effective performance of the detector.

To be compliant with ANSI/UL 2075, life-safety professionals should ensure their chosen system-connected CO detectors incorporate an integral trouble relay that sends a trouble signal to the control panel when the CO sensor has reached its EOL. This can be a point of confusion for professionals, because smoke detectors generally do not have limited-life components.

In addition, in all system-connected CO detectors manufactured after Sept. 1, 2009, the terminal screws must facilitate the required wiring supervision provisions of the UL standard. ANSI/UL 2075 requires the terminal screws to consist of binding screws with terminal plates having upturned lugs (see “CO Detector Wiring Requirements” diagram above). This method prevents the conductor from being wrapped around the terminal screw and requires the interruption of the wiring continuity when connection to the detector is lost. CO detectors that have pigtails are not acceptable.

Keep in mind that hardwired CO detectors with the UL 2075 mark manufactured prior to Sept. 1, 2009, may not be compliant with the new product standard.

The International Code Council (ICC) has also published new requirements for CO detection. These provisions are covered in the ICC’s International Residential Code (IRC) for one- and two-family dwellings and townhouses. The ICC codes are rapidly becoming the preference for state and local governments that adopt and enforce building code standards.

This new IRC mandate also requires CO detectors to meet the ANSI/UL 2034 standard and will go into effect with governmental unit adoption of the 2009 edition of the IRC. It is important to note even though the 2009 edition of the IRC references single-station CO alarms, it should not prevent UL 2075-listed, system-connected CO detectors from being used. This is because UL 2075-listed, system-connected CO detectors are required to have the same alarm thresholds as UL 2034-listed CO alarms, and the 2009 edition of NFPA 720 references UL 2075 system-connected CO detectors as acceptable. <p>

Yet, municipalities such as Chicago have had CO mandates for more than a decade. And state laws and local ordinances requiring CO alarms in residences and other dwellings have been enacted in hundreds of communities. The long lag time is due, in part, to the insufficient technical data to support the mandatory installation of CO alarms. The IRC committee also urged the industry to address the issues of reliability and false-positive indications.
Two important documents changed the course of the IRC’s CO detection mandates. First, technical data from a UL study supports the reliability and false alarm immunity of CO alarms.

This five-year UL research work, titled “Carbon Monoxide Alarm Field Study,” evaluated the effectiveness of CO alarms. The study concluded that CO alarms provide effective signaling protection when there are dangerous concentrations of CO. In addition, the study demonstrated that CO alarms generally do not emit false alarms in the field.

Secondly, in 2006 the Technical Committee for NFPA 720, Standard for the Installation of Carbon Monoxide Detection and Warning Equipment, conducted a complete rewrite of the standard in order to keep up with the trend in state legislation requiring the installation of CO detectors. The adoption of the 2009 edition of NFPA 720 provides the industry with a national CO detector installation standard for all buildings, not just dwelling units. NPFA 720 adds credibility to the reliable performance of CO detectors.

The new requirements will benefit the fire/life-safety industry by improving the performance of detectors, but more importantly, will enhance life safety for the public in the years to come.

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