Automatic Fire Detectors Do we really need a detector Kerosene Kerosene Speed & Aftermath of Fire Yes Fire Detectors detect fires at their earliest stages and sound a loud warning to help you get out safely Detection • Typical room • Typical room Alarm bell Corridor Stair pressurisation fan Fire escape stair Fire AlarmPanel Bell • Typical room in hotel Alarm bell Corridor Stair pressurisation fan Fire escape stair Fire AlarmPanel Bell Detector Sprinkler • Fire starts in room • • • • Smoke detector activates alarm Smoke fills guest room Alarm sounds in rooms and at lobby Stairway fan pressurisation begins • Occupants make way to stairwell • Smoke slowly spills into corridor • Stairwell provides SAFE egress path to outside of building • Sprinklers in room operate, discharging water, controlling and extinguishing fire • Occupants exit from building • Occupants leave building to safe area • Smoke is discharged from building Detection Detectors sense the existence of a fire Fire Panels acknowledge the detectors, test the system, check for faults operate the alarms Alarms inform the occupants of a fire and assist the evacuation 1. Concentration of energy Ignition and fire growth 2. Source of oxygen 3. Spontaneous oxidation at surface of combustible material 4. Release of particles into atmosphere 5. Exponential propagation of chain reaction 6. Release of energy in the form of light and heat Fire Growth VISIBLE SMOKEFLAMING FIRE INTENSE HEAT STAGE 1 STAGE 2 SMOKE DENSITY AND HEAT OUTPUT INCIPIENT STAGE - NO VISIBLE SMOKE TIME STAGE 3 STAGE 4 Detectors Smoke Flame Heat CO Smoke Detector Detects the presence of smoke particles Inexpensive, early detection for smouldering fires No need for line of sight Indoor applications only Subject to occassional false alarms Smoke Detector Ionisation Optical Beam Sampling Installed every 10m Ionisation Smoke Detector ION-CHAMBER SMOKE Alpha source Collector Battery Chamber cover Working of Ionisation Detector Smoke Detector Double Chamber Ionization Detector OPTICAL SMOKE Insect Screen Insect Screen Fins Smoke Path Sampling Volume Optical Detector Light Scatter Type Optical Detector Obscuration Type Sampling Detector What is an Air Sampling System? Air samples are drawn into the sampling pipe and carried through to the Detector by the aspirator. Detail of Sampling point Sampling pipe Sampling point Air samples VESDA Very Early Smoke Detection Apparatus Display Air enters detector Inlet manifold Ultra pure air is used to keep optical surfaces clean Laser Chamber Air sample is moved through the laser chamber via the aspirator and filter The signal is then passed to the Dual Stage Filter processor card for and onto the Display Dust is filtered Module out Aspirator ® Operation of the VESDA Detector Radiation / Flame Detectors Forms of radiant energy produced by a fire Detects radiation from flame Flame Detector Analyses one or more UV or IR frequencies Extremely fast on flaming fires Long range, line of sight Sophisticated and expensive Suitable for high risk, liquid and gas hazards Infra-red (IR) Radiation Detector Scanning Infra-red (IR) Radiation Detector Ultra-violet (UV) Radiation Detector FALSE ALARMS • Ultra Violet –Welding –X-ray –Lens contamination –High power consumption • Infra Red –sunlight Heat Detector Senses temperature or temperature change Immune to false alarms in most cases Reliable, fairly slow detection Fire must be near detector Low maintenance Inexpensive Heat Detector Fixed temperature Rate-of-rise Heat Detector Expansion of single metal strip Heat Detector Expansion of single metal strip Heat Detector Expansion of bi-metallic strip Heat Detector Expansion of gases Heat Detector Expansion of gases Heat Detector Linear Heat Detecting Cables Optical Fibre Distributed Temperature Sensing • Technology provides continuous profiles of temperature using a single optical fibre as the sensing element • An instrument containing an Optical Time Domain Reflectometer and signal processing software • Monitors hundreds of points in seconds • Sensor is insensitive to EMI • Sensor is Intrinsically safe Beam Detectors Effects of Flame on IR Beam Effects of Smoke on IR Beam Carbon Monoxide Detector CO is a toxic gas CO is the major cause of death in fires CO detectors sense slow smouldering fires before smoke detectors Best option for hotels, hospitals, nursing homes CARBON MONOXIDE SOMETHING NEW IN FIRE DETECTION? FACTS Carbon Monoxide Gas – Produced in fires – Odourless – Colourless – Travels more freely than smoke – Makes victims lethargic, disoriented – Brain damage, death at high ppm FACTS Slow Smouldering Fires – Vast quantities of CO before flaming – Cause of many deaths – Difficult to detect using traditional Ion- or Optical based detectors – Cause of backdraft? Fire Growth INCIPIENT STAGE - NO VISIBLE SMOKE VISIBLE SMOKEFLAMING FIRE INTENSE HEAT STAGE 1 STAGE 2 STAGE 3 STAGE 4 SPRINKLER SMOKE DENSITY AND HEAT OUTPUT BEAM PHOTO VESDA ION TIME FLAME HEAT Call Points Allow manual alarm of fire Different types include: Breakglass Push button Lever Located at exits and throughout risk Panels Panels are the “Brains” that receive the detector inputs and decide the action or output response The panels and detectors are configured into SYSTEMS There are two types of system configurations: CONVENTIONAL and ADDRESSABLE Conventional systems • Simple installation • Detectors and inputs are grouped into ZONES 2 Core • Each detector and input is individually Addressable identified Systems • One wire connects different types of inputs 2 Core Outputs • Alarms • Bells • Sirens • Lights • EVAC systems • Voice commands for regulated evacuation • Drivers for control • Suppression system • Shutdown of air handling • Control of doors Prevention issues Selecting Detectors Life safety, Business interruption, Asset protection, Explosion prevention Tolerable damage levels ? Fire issues Slow or rapid development Smouldering or flaming Solids or liquids Analyse relative importance of: Speed of response Selecting Detectors Range of response Sensitivity and discrimination Reliability General immunity to false alarm sources Immunity to specific radiation sources Electronic interface Cost Early Detection leads to Life Safety
