Is there any specific reason not to use abort switches on carbon dioxide system as per NFPA-12 18.104.22.168 "Abort switches shall not be used on carbon dioxide systems."
The primary reason that abort switches are prohibited on carbon dioxide systems is personnel safety. The basic purpose of an abort switch is to prevent the discharge of fire extinguishing agent while the cause of an alarm can be investigated.
The proper location of an abort switch is inside the protected space so the operator of the abort switch can see the hazard being investigated. Such a location also helps prevent unauthorized operation of the control (e.g. an arsonist using the control from outside the space while a fire rages within the space). In the case of a CO2 system, an abort switch properly located within the protected spaces places the operator in a position where the operator could be exposed to the discharge of CO2 with the attendant safety risks. This is because:
1) Upon release of the abort switch it is possible to have an immediate discharge of CO2 and the operator of the abort switch may not be able to evacuate the protected space before being exposed to possibly lethal concentrations of CO2.
2) Every CO2 system is equipped with a fully mechanical or pneumatic emergency manual release (EMR) which bypasses the electrical controls, hence bypassing the abort switch, and causes the CO2 system to discharge. A person operating the abort switch may believe that the CO2 system will not discharge while another person could operate the EMR and cause the system to discharge, bypassing the abort function. It is possible that the operator of the abort switch would not realize that the system is discharging until a potentially lethal concentration of CO2 is developed in the space.
Consideration of personnel safety is the primary reason abort switches are not permitted in systems designed in accordance with NFPA 12.
Taken from the Publication of Global Asset Protection Services LLC titled GAPS Guidelines - GAP.13.3.1 - CARBON DIOXIDE SYSTEMS
Although lockouts for safety purposes are acceptable, abort switches are not permitted. The nature of the hazard is usually such that a delay for investigation or improper use of an abort switch could bring about excessive damage prior to the attempt at extinguishment
The only personal protection provided by NFPA 12 is signs:
I must differ with the statement that "the only personal protection provided by NFPA 12 is signs." The various other personnel safety measures included in NFPA 12 should not be missed. Personnel safety has been a major consideration of the NFPA 12 technical committee for all of the forty-one years I have sat on that committee. Signs, alarms (referenced in the example of a warning sign shown in the previous post), lockout valves, time delays, requirements for personnel training, use restrictions . . . all of these are examples of the personnel protection measures required by NFPA 12. Regarding the original question, the rational behind prohibiting abort switches in CO2 systems is likewise rooted in consideration of personnel safety. One can also find this rational spelled out on page 14 of the "FSSA General Information Guide for Carbon Dioxide Fire Extinguishing Systems."
It is very important to recognize and implement all of the applicable personnel safety measures required by NFPA 12 when using carbon dioxide in a fire extinguishing system.
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