One of the more significant changes in NFPA 720: 2012 relates to sensitivity testing. The Technical Committee accepted a proposal to delete the sensitivity testing requirements for CO detectors. The Committee’s rationale is that no data has been provided at this time showing CO detectors experience a degradation of detection performance over time due to the sensitivity shifting. Furthermore, the CO sensing cell of all CO detection devices are required to be replaced after a certain period of time, usually between 6 to 10 years. Therefore, the requirement for sensitivity testing in the 2009 edition of the standard seemed to provide limited value or benefit.
Speaking of the CO sensing element, there are three basic types of CO sensing cells used today: biomimetic, metal oxide semiconductor (typically referred to as MOS sensors), and electrochemical. Regardless of the sensing technology, all CO sensors used in single- and multiple-station CO alarms and system-connected CO detectors have a limited life. The life span ranges from 6 to 10 years depending on the sensing technology and the manufacturer. ANSI/UL-2034 requires all CO alarms to indicate an audible end-of-life signal that is different from the alarm audible signal. ANSI/UL-2075 requires all system-connected CO detectors to provide a means to send the sensor’s end-of-life signal to the Control Unit. Typically, the end-of-life signal is triggered either by an internal timer or by a self-diagnostic test.
It’s important to point out that functional test requirements remained in the 2012 edition of the standard. This provision requires all CO “detectors” installed after January 1, 2012, to be functionally tested at initial acceptance and annually by introduction of CO gas into the sensing chamber. An electronic check by magnets or buttons or other analog values is not sufficient to comply with this requirement.
There are also new secondary power supply requirements for CO detection systems. The base requirements in the 2009 and 2012 edition of NFPA 720 are considerably different than fire alarm systems, and at first glance, seem to be excessive. CO detection systems are required to have sufficient secondary power to operate the system under normal, non-alarm condition for 24 hours and, at the end of that period, be capable of operating all of the notification appliances for 12 hours if the system is not monitored by a supervising station. If the system is monitored by a supervising station, the secondary power is permitted to be reduced from 12 hours to 60 minutes in the 2009 edition. For the 2012 edition, the secondary power of a CO detection system is permitted to be reduced to 5 minutes of alarm, just like a fire alarm system, if it’s monitored by a supervising station.
The Committee accepted a proposal to require a 520 Hz low-frequency tone to awaken people with hearing loss. By accepting this proposal, the audible CO alarm signal in sleeping areas will correlate with the fire alarm audible alarm signal requirements in the 2010 edition of NFPA 72®. The 520 Hz CO alarm signal is required after January 1, 2015, where audible appliances are provided in commercial sleeping areas. For CO alarms or household CO detection systems, the 520 Hz tone shall be provided voluntarily for those with hearing loss or where required by governing laws or codes. These new requirements are based on several research studies supported by the Fire Protection Research Foundation that have shown a 520 Hz tone can awaken and alert people with hearing loss, as well as alcohol-impaired adults. Currently, most CO and fire alarm audible tones produce a high frequency 3 KHz tone by using a piezoelectric sounder. This 3 KHz frequency band is not as effective at awakening people with hearing loss, alcohol-impaired adults or older adults.
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Tags: Carbon monoxide, Code, NFPA
Posted in Carbon Monoxide Detection, NFPA, Summer 2012
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