Heat Transfer and Safety Management Quiz

Fire Protection and Security

• Combustion: The rapid exothermic or heat-producing chemical reaction of oxygen with a fuel.
• Heat of combustion: The amount of heat released as a result of complete combustion of a fuel.
• Heat transfer by radiation: Electromagnetic mechanism of heat transfer. The amount of heat transfer is proportional to the fourth power of temperature.
• Convection: When a cold fluid comes into contact with a hot surface, the film adjacent to the hot surface picks up thermal energy. This energy, in turn, is transmitted to the bulk of the cold fluid either by natural mixing or as a result of external forces.
• Conduction: The mechanism of thermal energy transfer from one molecule to another by direct contact.
• Thermal conductivity: The ability of an object to transfer heat. Different materials have different thermal conductivities; for example, metals have high thermal conductivity and are good conductors of heat, whereas plastics generally have low thermal conductivity and are poor conductors of heat (good insulators).
• Four elements of combustion (fire tetrahedron): Oxygen, fuel, chemical reaction, and heat.

Flammable Liquids

• Flammable liquid: A liquid with a flash point below 100°F and a vapor pressure not exceeding 40 psia (pounds per square inch absolute) at 100°F.
• Combustible liquid: A liquid with a flash point at or above 100°F.
• Flash point: The lowest temperature at which a liquid can generate enough vapor above its surface to support combustion in the presence of a source of ignition.
• Vapor pressure: The pressure exerted by a vapor on its liquid at equilibrium.
• Fire point: The lowest temperature at which a flammable liquid in an open container gives off enough vapors to continue to burn once it has been ignited.

Fire Prevention

• Lower Flammability Limit (LFL): The minimum concentration of vapor in air below which a flame will not propagate through the mixture. A decrease in temperature or pressure raises the LFL. An increase in temperature lowers the LFL.
• Upper Flammability Limit (UFL): The maximum concentration of flammable vapor in air above which a flame will not propagate. A decrease in temperature or pressure raises the UFL. An increase in temperature raises the UFL.
• Auto ignition temperature: The lowest temperature that will produce combustion in the absence of an ignition source.
• Specific gravity: The density of a liquid relative to the density of water.
• Vapor Density: A measure of the relative densities of vapors and gases compared to air under the same conditions of temperature and pressure.
• Evaporation rate: The rate at which a liquid is converted to vapor at a given temperature and pressure.
• Water solubility: Many flammable liquids such as alcohols, ethers, and ketones are completely or partially soluble in water.
• Flammable gases: A gas is considered flammable if at ambient temperature and pressure it has a UFL of 13% or less by volume.
• Carbon monoxide (CO): Colorless, odorless, and toxic flammable gas that is formed through incomplete combustion of carbon.
• Carbon dioxide (CO2): Fires produce large amounts of carbon dioxide. It's a simple asphyxiant.
• Hydrogen cyanide (HCN): Can be produced during fires from wool, silk, acrylonitrile, etc.
• Sulphur dioxide (SO2): Can be produced during fires from the combustion of sulfur containing materials. Strong irritant
• Ammonia (NH3): Generated from the combustion of materials such as wool, silk, fertilizers, explosives, acrylonitrile and nylon.
• Hydrogen chloride (HCl): Generated from combustion of polyvinyl chloride (PVC), dyes, perfumes and agricultural chemicals.
• Hydrogen sulfide (H2S): Result of incomplete combustion of sulfur compounds such as wool and rubber.
• Nitrogen dioxide (NO2): Generated from combustion of nitrogen containing compounds such as fabrics, cellulose nitrate, etc.

Fire Extinguishers

• Class A fire extinguishers: Used for common combustibles such as wood, cloth, paper, rubber, and plastics. Use water.
• Class B fire extinguishers: Used for flammable liquids and gases. Use dry chemicals, carbon dioxide and halons.
• Class C fire extinguishers: Used for energized electrical equipment. Use nonconductive agents.
• Class D fire extinguishers: Used for combustible metals. Use extinguishing agent that absorbs heat without reacting with the metal.
• Class K fire extinguishers: Used for cooking fats, greases, and oils.

Sprinkler Systems

• Dry pipe sprinkler system: The sprinkler heads are attached to piping that contains air or nitrogen under pressure.
• Wet pipe sprinkler system: The sprinkler heads respond to the heat generated from a fire.
• Pre-action automatic sprinkler system: Controlled by an automatic fire detection system.
• Deluge sprinkler system: The sprinkler heads are open at all times.
• Combined dry pipe and pre-action systems: Combines the essential features of both dry pipe and pre-action systems.
• Residential sprinkler systems: Designed for use in residences.

Fire Detection

• Fixed temperature detectors: Detect fires based on the rising temperature in the surrounding area.
• Rate-of-rise detectors: Detect fires based on the rate of temperature increase.
• Rate compensation detectors: Respond to a fixed predetermined temperature in the air surrounding the device.
• Sealed pneumatic line-type detectors: Completely mechanical, among thermal detectors; ideal for locations where electricity must be avoided.
• Smoke detectors: Detect the presence of smoke and/or combustion products. These can be photoelectric or ionization detectors.
• Flame detectors: Detect the presence of flames.