Safety Engineering. Fire Protection Systems and Life Safety Systems

Transcription

1 Safety Engineering Fire Protection Systems and Life Safety Systems

2 Introduction 2 A key aspect of fire protection is to identify a developing fire emergency in a timely manner, and to alert the building's occupants and fire emergency organizations. This is the role of fire detection and alarm systems. Depending on the anticipated fire scenario, building and use type, number and type of occupants and criticality of contents and mission, these systems can provide several main functions: First, they provide a means to identify a developing fire through either manual or automatic methods. Second, they alert building occupants to a fire condition and the need to evacuate. Another common function is the transmission of an alarm notification signal to the fire department or other emergency response organization. They may also shut down electrical, air handling equipment or special process operations, and they may be used to initiate automatic suppression systems.

3 Electronic Fire Signalisation 3 is an important part of fire protection systems ensures early and rapid identification and localization of the fire given by the project documentation, which is based on the fire protection of the objects EFS systems Conventional the system recognizes only a fire compartment, suitable for smaller objects to limit false alarms Addressable system accurately determine which detector reports Detectors conventional - detectors with a fixed fire alarm value (common detectors - switch) analog - detectors monitor the environment and evaluate the change

4 Electronic Fire Signalisation 4 Detection Systems Action Systems fire extinction ventilation... Notification Systems

5 Electronic Fire Signalisation 5

6 Manual Fire Detection - Pull Stations 6 = oldest method of detection (the simplest form) a person yelling can provide fire warning The general design philosophy is to place stations within reach along paths of escape. Advantage - provide occupants with a readily identifiable means to activate the building fire alarm system. Disadvantage - they will not work when the building is unoccupied.

7 Automatic Detectors 7 General method Heat/Thermal Detecting the unique optical characteristics of flames Distinguishing between flame radiation and background radiation

8 Automatic Detectors - Heat Detectors 8 Introduction Heat detectors are the oldest type of automatic fire detection device. They began development of automatic sprinklers in the 1860s. A heat detector is best situated for fire detection in a small confined space where rapidly building high-output fires are expected, in areas where ambient conditions would not allow the use of other fire detection devices, or when speed of detection is not a prime consideration. Heat detectors are generally located on or near the ceiling and respond to the convected thermal energy of a fire. They respond either when the detecting element reaches a predetermined fixed temperature or to a specified rate of temperature change.

9 Automatic Detectors - Heat Detectors 9 Fixed temperature Fixed-temperature heat detectors are designed to alarm when the temperature of the operating elements reaches a specific point. Fixed-temperature heat detectors are available to cover a wide range of operating temperatures - from about 57 C and higher. Rate-of-Rise temperature One effect that flaming fire has on the surrounding area is to rapidly increase air temperature in the space above the fire. The rate-of-rise detector will function when the rate of temperature increase exceeds a predetermined value, typically around 7 to 8 C per minute.

10 Automatic Detectors - Heat Detectors Combination 10 Combination detectors contain more than one element which responds to fire. An example of the former is a heat detector that operates on both the rate-of-raise and fixed-temperature principles. Its advantage is that the rate-of-rise element will respond quickly to rapidly developing fire, while the fixed-temperature element will respond to a slowly developing fire when the detecting element reaches its set point temperature.

11 Automatic Detectors - Heat Detectors - principles Thermocouples 11 Thermocouples are thermoelectric sensors that basically consists of two junctions of dissimilar metals, such as copper and constantan that are welded or crimped together. When fused together the junction of the two dissimilar metals such as copper and constantan produces a thermo-electric effect which gives a constant potential difference of only a few millivolts (mv) between them. Then the output voltage from a thermocouple is a function of the temperature changes. The output voltage from a thermocouple is very small, only a few millivolts (mv) for a 10 C change in temperature difference and because of this small voltage output some form of amplification (Operational Amplifier) is generally required. Source:

12 Automatic Detectors - Heat Detectors - principles Thermocouples - Types 12 Source:

13 Automatic Detectors - Heat Detectors - principles Bi-metallic Strip When temperature increases, the bimetal curves as the metal with higher coefficient of expansion lying on the outer side of an arc undergoes a greater increase in length. With one end fixed, the movement of the free end of the strip can be arranged to close an electric circuit that operates an alarm. 13 Source:

14 Automatic Detectors - Heat Detectors - principles Thermistor A thermistor is a special type of resistor which changes its physical resistance when exposed to changes in temperature. 14 Thermistors are generally made from ceramic materials such as oxides of nickel, manganese or cobalt coated in glass which makes them easily damaged. Their main advantage over snap-action types is their speed of response to any changes in temperature, accuracy and repeatability. Example At 25 C At 100 C The thermistor has a resistance value of 10KΩ at 25 C and a resistance value of 100Ω at 100 C. Calculate the voltage drop across the thermistor and hence its output voltage (Vout) for both temperatures when connected inseries with a 1kΩ resistor across a 12 V power supply. Source:

15 Automatic Detectors - Heat Detectors - principles Resistance Thermometer, RTD 15 RTD s are precision temperature sensors made from high-purity conducting metals such as platinum, copper or nickel wound into a coil and whose electrical resistance changes as a function of temperature, similar to that of the thermistor. These devices have a thin film of platinum paste is deposited onto a white ceramic substrate. Their output is extremely linear producing very accurate measurements of temperature, but they have very poor thermal sensitivity, that is a change in temperature only produces a very small output change for example, 1Ω/ C. The more common types of RTD s are made from platinum and are called Platinum Resistance Thermometer or PRT s with the most commonly available of them all the Pt100 sensor, which has a standard resistance value of 100Ω at 0 C. Two-wire configuration Three-wire configuration Source:

16 Automatic Detectors Flame Detectors 16 Principles Each type of fuel, when burning, produces a flame with specific radiation characteristics. A flame detection system must be chosen for the type of fire that is probable. For example an ultraviolet (UV) detector will respond to a hydrogen fire, but an infrared (IR) detector operating in the 4.4 micron sensitivity range will not. It is imperative therefore; that a qualified fire protection engineer is involved in the design of these systems, along with assistance from the manufacturer's design staff.

17 Automatic Detectors Flame Detectors 17

18 Automatic Detectors Flame Detectors 18 Most of the energy is invisible to us. The part that we can see is mostly red-yellow caused by the Carbon in a fire. The invisible IR part of the fire we experience as heat. Energy, Kilowatt A non-hydrocarbon such as Hydrogen burns light bluetransparent (no Carbon in the flame). It also does not have the CO 2 peak at 4.4µ and can therefore only be detected with a UV or UV/IR detector. Near IR Visible UV Wavelength 4.4

19 Automatic Detectors Flame Detectors 19 The CO 2 peak in the fire represents less then 2% of the total fire energy. A multi sensor Flame Detector has much more sensor input and can therefore be more specific or less effected by false alarms. Energy, Kilowatt Near IR UV Visible Wavelength 4.4

20 Automatic Detectors Flame Detectors Devices 20 Specialized devices that detect the electromagnetic light waves produced by a flame. Typically found in places where early detection and rapid reaction to a fire is critical. Complicated and expensive. Each Optical Flame Detector (OFD) comprises one or more optical sensors sensitive to electromagnetic energy emitted at various wavelengths in different spectral bands. Most popular sensors are UV and IR solid state sensors used alone or in combinations to combat false alarms.

21 Automatic Detectors Flame Detectors Devices (optical sensors) Due to their fast detection capabilities, flame detectors are generally used only in high-hazard areas, such as fuel-loading platforms, industrial process areas, hyperbaric chambers, high-ceiling areas, and atmospheres in which explosions or very rapid fires may occur. Because flame detectors must be able to 'see' the fire, they must not be blocked by objects placed in front of them. The infrared-type detector, however, has some capability for detecting radiation reflected from walls. 21

22 Automatic Detectors Flame Detectors 22 Dual UV/IR Flame Detectors Two types of UV/IR optical flame detectors are available, each comprising a UV sensor and an IR sensor selected from one of the following: micron IR sensor (detects H 2 O radiation) micron IR sensor (detects CO 2 radiation) IR 3 Flame Detection Detection of the flame s characteristic CO 2 emission line by the use of three wavelength bands. Reference fire N-heptane Methane Hydrogen 65 m 30 m 30 m

23 Automatic Detectors Smoke Detectors A smoke detector is a device that senses the presence of smoke in a compartment and warns the occupants, enabling them to escape a fire before succumbing to smoke inhalation or burns. 23 A smoke detector will detect most fires much more rapidly than a heat detector. Photoelectric or optical smoke detectors work by generating pulses of infra red light and sensing any reflected light. If smoke is present in the sensing chamber the light is reflected by the smoke particles onto a photodiode which sense the presence of the smoke. The photoelectric detector senses the large, visible smoke particles. Source:

24 Automatic Detectors Smoke Detectors Ionization smoke detectors use a weak radioactive source to ionize the air between two electrodes, and allowing a small current to flow. Smoke particles reduce the current flowing in the ionization chamber. 24 Ionization smoke detectors are most sensitive to smoke with small (invisible) particles, of the type which is emitted by fast flaming fires. When disposing of the ionisation detector - it is hazardous waste, it requires a special treatment regime (placing in a special container, records of origin and special disposal in a designated laboratory, etc.)! Source:

25 Gas sensors 25 A sensor is a technological device that detects / senses a signal, physical condition and chemical compounds. It is also defined as any device that converts a signal from one form to another. Gas sensor measures the concentration of gas in its vicinity. Gas sensor interacts with a gas to measure its concentration. Each gas has a unique breakdown voltage i.e. the electric field at which it is ionized. Sensor identifies gases by measuring these voltages. The concentration of the gas can be determined by measuring the current discharge in the device.

26 Gas sensing technologies 26 Metal Oxide Based Gas Sensors Metal oxide sensors are also known as chemiresistors. The detection principle of resistive sensors is based on change of the resistance of a thin film upon adsorption of the gas molecules on the surface of a semiconductor. The gas-solid interactions affect the resistance of the film because of the density of electronic species in the film. Rely on a very well known property of metal oxides at elevated temperature to change their surface potential, and therefore their conductivity in the presence of various reducible gases such as ethyl alcohol, methane and many other gases, sometimes selectively sometimes not.

27 Gas sensing technologies 27 Metal Oxide Based Gas Sensors Fabrication is relatively simple. May be based on silicon processes or other thin or thick film technologies. The basic principle is that when an oxide is held at elevated temperatures, the surrounding gases react with the oxygen in the oxide causing changes in the resistivity of the material. The essential components are the high temperature, the oxide and the reaction in the oxide. CO sensor

28 Gas sensing technologies 28 Calorimetric Gas Sensors The principle of calorimetric gas sensors based on change in temperature at catalytic surfaces. It consists of a surface of a film of a catalytically active metal (e.g. Platinum, Palladium or Rhodium). It burns combustible gases. Heat is generated due to the combustion. This heat is balanced by a reduction in the electrical heating power. Thus the power consumption indicates the concentration of gas. The sensor is used for detection of methane, propane and other inflammable and toxic gases.

29 Gas sensing technologies 29 Gas Sensors thick films Advanced thick film technology, Au contacts, RuO or Pt heater, power consumption mw.

30 Gas sensors Location of sensors installation at a location where gas leakage is most likely 30 Examples Natural gas gas tends to rise and fill any spaces above the level of leakage the detector sensor element is to be installed above the level of the possible source of leakage and close to the ceiling (usually 0.3 m from the ceiling) where the air flow is not obstructed (by furniture or equipment). LPG (propane-butane) gas tends to fall and fill any spaces below the level of leakage the detector detector element to be installed is to be installed as low as possible (usually 0.1 m above the floor) at a location where air flow (by furniture or equipment) is not obstructed.

31 Gas sensors Location of sensors 31 The detector should not be installed in an enclosed space (eg in a cabinet) directly under the sink near a door or window near the extractor hoods in an area where the temperature may fall below -10 C or exceed 40 C where dust and dirt can pick up the sensor in damp or wet location

32 Alarms False, Unwanted, and Nuisance Alarms 32 Malicious False Alarms Caused by individuals who deliberately activate a fire alarm when there is no fire Unwanted Alarms Occur when an alarm system is activated by a condition that is not really an emergency Nuisance Alarms Caused by improper functioning of an alarm system or one of its components

33 Notification Systems Alarm Notification Appliances Occupants need to be provided with timely and accurate information so that they can understand the urgency of a particular event and make appropriate egress decisions. 33 Produce an audible signal when fire alarm is activated Some signals play a recorded announcement in conjunction with the temporal-3 pattern. Many new systems incorporate visual notification devices.

34 Fire Suppression Systems 34 Fire sprinkler systems Gaseous agents Wet and dry chemical agents Water Fire Sprinkler System In most automatic sprinkler systems, the sprinkler heads open one at a time as they are heated to their operating temperature. One of the major advantages of a sprinkler system is that it can function as both a fire detection system and a fire suppression system.

35 Fire Sprinkler Systems 35

36 Fire Sprinkler Systems Water Supply and Storage 36 Water may be supplied from the following: Underground supply mains from public water works Automatically or manually controlled pumps drawing water from lakes, ponds, rivers, surface storage tanks, underground reservoirs, or similar adequate sources Pressure tanks containing water Elevated tanks or reservoirs that depend on gravity to force water through the system Fire Department Connection (FDC) Allows the department s engine to pump water into the sprinkler system Used as either a supplement or the main source of water

37 Fire Sprinkler Systems Sprinkler Piping Network of pipes that delivers water to sprinkler heads. Includes main water supply lines, risers, feeder lines, and branch lines. Usually made of steel. Plastic pipe sometimes used in residential systems. 37 water sprinkler system water mist system

38 Fire Sprinkler Systems Sprinkler Heads 38 The working ends of a sprinkler system Composed of: A body, which includes the orifice (opening) A release mechanism that holds a cap in place over the orifice A deflector that directs the water in a spray pattern

39 Fire Sprinkler Systems Frangible Bulb Sprinkler Heads 39 Use a glass bulb filled with glycerin or alcohol to hold the cap in place. As bulb is heated, liquid absorbs the air bubble and expands until it breaks the glass, releasing the cap.

40 Fire Sprinkler Systems Water Sprinkler / Water Mist 40 Sprinkler head Mist nozzle A stream of droplets from the sprinkler diameter of 1-3 mm Spray water mist diameter of µm

41 Fire Sprinkler Systems Extinguishing capability 41 System Diameter of droplets [mm] The surface of the drops per liter of water [m 2 ] Splinkler 1 2 Spray 0,1 20 Mist 0, Heat removal from the vicinity of the fire 335 kj / kg of water heating from 20 C to 100 C kj / kg conversion of the liquid to steam Local inerting - water vapor 1 liter of liquid water produces 1700 liters of steam at atmospheric pressure (100 C)

42 Fire Sprinkler Systems Fire Suppression 42