Principles Of Operation; Introduction; Heat Detector Operation - Simplex 4098 Manual

normally conducted in that area. When a detector must be located in, or adjacent to such an area, a fixed temperature heat detector
can be appropriate.
• In air streams passing by or through kitchens. Air often enters a residence or a residential unit of an apartment building through
cracks around the front or back doors. If the air return is in the bedroom hallway or in the bathroom, and if air from the kitchen easily
enters the air stream going from the door to the air return, combustion particles from cooking can cause nuisance alarms. Install
detectors or sensors so that they protect the bedrooms but are out of the air stream.
• In or near manufacturing areas, battery rooms, or other areas where substantial quantities of vapors, gases or fumes may be present.
Strong vapors, like excessive humidity, can make detectors or sensors overly sensitive or less sensitive than normal. In very large
concentrations, gases heavier than air, such as carbon dioxide, may make detectors or sensors more sensitive, while gases lighter
than air, such as helium, may make them less sensitive. Aerosol particles may collect on detector or sensor chamber surfaces and
cause nuisance alarms.
• In insect-infested areas. If insects enter a detector or sensor's sensing chamber, they can cause a nuisance alarm. Perform insect
eradication procedures before installing detectors or sensors in these locations. If spraying is part of this process, do not allow insect
spray to enter the detectors or sensors.
• Near fluorescent light fixtures. Electrical noise generated by fluorescent light fixtures may cause nuisance alarms. Install detectors or
sensors at least 1 foot, or 0.3 meters away from these light fixtures.
• When using the CO Base for CO fire detection, do not install in locations that can have potentially high non-fire levels of CO.
Underwriters Laboratories (UL) has three standards for smoke detectors:
• One for duct detectors or sensors, UL 268A.
• One for single and multiple station detectors/sensors, UL 217.
• One for system type detectors or sensors, UL 268.
Only use detectors or sensors in the applications for which they are specifically listed.
The NFPA 101 Life Safety Code states that single station smoke detectors shall sound an alarm only within an individual living unit or similar
area and shall not actuate the building fire alarm system. It also states, "All systems and components shall be approved for the purpose for
which they are installed."
In addition to possible code noncompliance, the following deficiencies exist in a series of residential smoke detectors connected in a fire
alarm system mode:
• Because the fire alarm system is not supervised, vandals or others can disconnect a detector or the entire system, leaving a building
without protection. In this situation the residents are unaware of the serious life threatening condition.
• Residential detectors do not latch in alarm, the detector self-resets. One detector in alarm sounds all the detectors that are
connected together. In this situation, after the alarm condition is cleared, it is difficult to identify or locate a specific detector that
initially put the system into alarm,.
System detectors or sensors latch in alarm. They do not reset until the power is momentarily disconnected. This makes it easier to identify
the location of the detector or sensor that caused the control panel to alarm. In addition, system detectors are specifically designed to
connect to a supervised control panel. Two-wire detectors require a UL compatibility review to verify that the detector and panel operate
correctly together.
A typical life safety fire alarm system for an apartment complex uses system detectors or sensors and manual fire alarm stations in the
hallways and common areas of the complex, and residential single station type detectors and heat detectors in the individual apartments.
The system detectors or sensors, manual stations and heat detectors are connected to a supervised control panel, sound a general
alarm, and automatically notify the proper authorities that a fire condition exists. The residential detectors located in the apartments are
interconnected only within the individual living quarters of each apartment. These residential units sound an alarm only in the apartment
unit.
2.4

Principles of operation

2.4.1

Introduction

This section describes how the different types of detectors and sensors work. For additional information about TrueAlarm sensor
operation, refer to the TrueAlarm Concepts publication (PER-91-024).
2.4.2

Heat detector operation

The heat detector senses the heat or the Rate-of-Rise (ROR) in the air temperature of the environment in which it is located. The heat
detector is comprised of electronic circuitry and a mechanical package that is designed to sense the ROR of the air temperature in an
expedient and reliable fashion. Upon detection of an abnormal increase in air temperature, or ROR in air temperature, the electronics
indicate an alarm by increasing the amount of current draw from the monitor zone it is connected to. The monitor zone is a supervised
page 8
4098 Detectors, Sensors, and Bases Application Manual
574-709 Rev. AP