Consulting-Specifying Engineer - July 2008 - (Page 61)

Equipment Lifecycles Today’s architectural design has challenged alarm designers with assignment of proper smoke detector coverage. When determining placement of detectors, NFPA 72 defines proper location and spacing and provides installation parameters that cover ceiling heights, types of ceilings, and obstructions, and provides minimum requirements for proper smoke detector placement. This national code is adopted by most, if not all, contemporary model building codes and should be referenced by all alarm designers. Often overlooked, manufacturers’ installation requirements—as referenced by the device’s listing organization—are vital to correct operation. The manufacturers have had the smoke detectors tested and listed with Underwriter’s Laboratory (UL) for most installation scenarios. This should be one of the first references for design consideration; otherwise, additional costs may be incurred if detectors need to be relocated or removed. Manipulation of a previously installed detector could subject the detector to contamination and could the detector’s lifespan. Installation and interferences The installation contractor should be aware of issues the smoke detector or smoke detector wiring can create if installed in an incorrect location. Smoke detectors that are installed within 1 ft of a fluorescent light can cause nuisance alarms. The fluorescent light generates an electrical interference that affects the smoke detector’s sensing chamber electronics. Additionally, the fire alarm wiring to the smoke detector must be properly separated from lighting circuits as defined in NFPA 70 (National Electric Code). The lighting circuit wiring generates an electrical interference that can create noise on the fire alarm wiring. This also can be picked up by the smoke detector’s sensing chamber and cause nuisance alarms. In most cases when this problem occurs, the first solution is to replace the smoke detector instead of properly troubleshooting the problem and relocating smoke detector and/or of the outputs (programmable modules). the fire alarm wiring. If basic separation This process is known as establishing the requirements were followed at installation, sequence of operations. the lifespan of the original smoke detector Part of the sequence of operations can be would not have been affected. to activate alarm verification or adjust the Installation too close to air diffusers obscuration levels of the smoke detectors. can shorten the life of a smoke detector. Alarm verification is a process that is proWhether the diffuser is a supply or return, grammed to the smoke detector in which the air movement near the diffuser is strong an alarm condition must exist for a prederelative to other places within a building, termined period of time prior to notifying carrying more dirt and dust (contaminants) the fire alarm panel that the smoke detector than normal. The dirt and dust will tend has an alarm condition. Adjustment of the to build up faster within smoke detectors obscuration level is setting the sensitivity when they are too close to an air diffuser. This can result in nuisance alarms or trouble signals, and if the detector is not properly maintained, it will have a shorter life. Lastly, the installation of smoke detectors should be done when all construction trades have properly cleaned the construction debris. However, most projects undertaken these days will not allow the installation con- Smoke detectors should be commissioned after installatractor the appropriate time tion to ensure functionality and sequence of operations. to install the devices after Photo: System Sensor construction clean-up. As a result, protective coverings supplied with level of the smoke detector. Most fire alarm the detectors should be left installed until panels have a low-, medium-, and high-senconstruction clean-up is completed. This will sitivity adjustment. maintain the integrity of the detector while The alarm verification and the sensitivity high contamination potential is present, adjustment can reduce nuisance alarms and thus prolonging the life of the detector. It relieve the requirement for smoke detecis important to note that these protective tor replacement, thus prolonging the life covers are not UL listed to protect a smoke of the detectors. These options are available detector from contaminants, and some on most fire alarm panels, but it is the AHJ authorities having jurisdiction (AHJ) will who approves the use of alarm verification not accept this type of contamination pro- or adjustments in the smoke detector sentection; all jurisdictions will require impair- sitivity levels. These programming changes ment procedures to be followed. should be applied cautiously, in consideration of the detector’s expected safety funcSet-up and commissioning tion, and are not a replacement for good The next step in the process of install- judgment and consideration of environing smoke detectors is to program the mental considerations. If misapplied, these fire alarm system for the smoke detec- programming changes can mask issues that tors. This includes setting up the inputs can shorten the lifespan of a spot-type (smoke detectors) to control the sequence smoke detector. Consulting-Specifying Engineer • JULY 2008 61

Table of Contents Feed for the Digital Edition of Consulting-Specifying Engineer - July 2008

Consulting-Specifying Engineer - July 2008 Contents Viewpoint Letters News M/E Roundtable 40 Under 40 Using Demand-Based Reset Strategies VFDs and Motors: Making the Right Match Grounding and Bonding Practices for Hazardous Areas Codes & Standards Case Study New Products Equipment Lifecycles Advertiser Index Green Space

Consulting-Specifying Engineer - July 2008

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