Fenwal Controls DAF DETECT-A-FIRE Heat Detectors

DETECT-A-FIRE (D-A-F) detectors are the “heart” of many fire protection systems. The highly reliable D-A-F has been the standard for over 75 years. The D-A-F is used for signalling overheat or fire conditions. In the vast majority of applications, the D-A-F provides the initial heat sensing that activates suppression systems using clean agents, CO2, inert gases, wet or dry chemicals, or water.

D-A-F detectors are widely accepted because they are designed with rate compensation. This provides a unique advantage over both fixed-temperature and rate-of-rise detectors because the D-A-F detector accurately senses the surrounding air temperature regardless of the fire growth rate. At the predetermined set point, the system is activated.

Fixed-temperature detectors must be fully heated to the alarm temperature so that a response lag may occur during a fast-rate fire. Rate-of-rise devices, on the other hand, are triggered by the rate of increase in ambient temperature and are subject to false alarms caused by harmless, transient thermal gradients such as the rush of warm air from process ovens.

The key to the detector’s sensitivity is in the design. The outer shell is made of a rapidly expanding alloy which closely follows changes in surrounding air temperature. The inner struts are made of a slower-expanding alloy. Designed to resist heat absorption and sealed within the shell, the struts respond more slowly to temperature changes.

A slow-rate fire (Figure 2) will heat the shell and struts together. At the “set point”, the detector will trigger, actuating the alarm or releasing the extinguishant. A transient rush of warm air up to 40°F/min. May expand the shell without triggering the detector. By ignoring transient warm-air excursions, the D-A-F detector virtually eliminates false alarms prevalent in rate-of-rise devices.

If a fast-rate fire (Figure 3) starts, the shell will expand rapidly. The struts will close, actuating the alarm and/or releasing the agent. The faster the fire rate of growth, the sooner the D-A-F detector will react.

Vertical DETECT-A-FIRE Detector

Vertical D-A-F detectors are designed for use in both “ordinary” or “hazardous” locations. For “ordinary” use, they may be mounted to any approved junction box with a 7/8″ diameter opening by using 1/2-14 NPT mounting nuts. The device may be wired in or out of conduit, depending on local preferences and codes. To facilitate supervision of system wiring, four lead wires are provided on normally open vertical detectors (that close on temperature rise). When mounted in an appropriately classified mounting box, detectors are Underwriters Laboratories and Underwriters Laboratories of Canada listed and FM Approved for hazardous locations.

Horizontal DETECT-A-FIRE Detector

Horizontal D-A-F detectors are designed for locations where appearance is a factor. The low-profile, functional design provides physical protection for the detector while making it suitable for commercial, industrial, mercantile, public buildings, institutions, and marine applications in non-hazardous locations (those classified as “ordinary” under the National Electrical Code). Flush-mounted detectors are designed to fit standard 4-inch octagonal electrical boxes, and surface-mounted detectors are designed to mount directly on ceilings or on 4-inch electrical junction boxes. Canadian Electrical Codes require mounting only to an electrical junction box.

Features

• Economical: wide spacing reduces installation costs.
• Factory set.
• Internal contact area hermetically sealed in a stainless steel shell.
• ROHS Compliant.

Applications

• Protection of schools, factories, offices, libraries, or other non-residential buildings.
• Power generation.
• Gas station islands.
• Paint spray booths.
• Range hoods.
• Engine compartments.

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