Fire Development Stages and Volumetric Motion Detectors

Fire Development and Behavior

Understanding the stages and behavior of fire development is essential for timely detection and hazard mitigation.

Latent Stage

In the latent stage, there is no visible fire or flame production. Combustion particles are generated that are invisible to the human eye. This phase can last from minutes to several hours. It carries severe danger because it cannot be easily detected or extinguished without specialized equipment.

Visible Smoke Stage

During the visible smoke stage, the generation of combustion particles increases significantly, making them visible to the human eye as smoke. This stage can also last minutes or hours before active fire breaks out, and it poses significant hazards to occupants.

Flame Stage

The development into the flame stage depends heavily on environmental conditions, especially available oxygen levels, which dictate whether fire can develop rapidly. The progression time depends directly on the combustible materials involved, developing within seconds or minutes.

Heat Stage

In the heat stage, the highest thermal intensity most often coincides with the peak intensity of open flames, dense smoke, and toxic gas emission. This stage advances extremely fast within just a few seconds and represents a critically dangerous phase of fire growth.

Signaling and Auxiliary Elements

Alarm infrastructures rely on specialized signaling indicators and auxiliary contacts to effectively coordinate emergency responses.

Fire Signaling Elements

Signaling elements and action indicators (remote pilot lights) are installed when protected enclosures are closed. It is advisable to use them to inform personnel from the outside via pilot indicators that a specific detector inside the room or zone is in an alarm state, identifying the triggered detector line or zone.

Auxiliary Elements

Auxiliary elements in fire alarm control panels feature output terminal strips equipped with voltage-free relay contacts. These contacts activate in an alarm situation in one or more zones or wings, enabling direct connection to external auxiliary equipment and control systems.

Volumetric Motion Detectors

Volumetric detectors are placed in primary zones that require protection, with the objective of detecting unauthorized movement within a defined space.

Radar, Microwave, and Ultrasonic Sensors

Radar, microwave, and ultrasonic detectors base their operation on transmitting a signal at a constant frequency. When this signal is disturbed or altered, the detector identifies the change and triggers the central alarm system:

• Radar detectors: Utilize an emission system based on radio frequency waves.
• Microwave detectors: Operate with high-frequency signals situated in the microwave band, typically around 10 GHz.
• Ultrasonic detectors: Operate with acoustic waves in the ultrasonic field between 20 kHz and 40 kHz. They consist of a transmitter that emits acoustic waves that reflect off objects in the protected zone and bounce back to the detector's receiver.

Infrared Motion Detectors

Infrared detectors base their operation on the reception of electromagnetic waves in the infrared spectrum, which are not visible to the human eye. They are composed of a phototransistor paired with a front-mounted lens designed to focus and expand coverage. When an intruder moves within the room, it produces a thermal variation in the ambient radiation; this shift is captured by the detector and sounds the alarm.

Installation Considerations

When installing volumetric sensors, several essential precautions must be observed:

• Protect the unit from direct sunlight and excessive heat sources.
• Avoid placing the sensor directly in front of physical obstacles.
• Position the device perpendicular to the expected entry path of an intruder.
• If domestic animals or pets are present in the area, mount detectors at a higher elevation.

Dual-Technology Detectors

Dual-technology detectors are deployed when environmental conditions make choosing a single sensor type difficult or when absolute certainty is required to prevent false alarms. These units sound the alarm only when both sensing technologies detect an intruder simultaneously. They typically combine passive infrared and microwave sensing elements.