Flashcards
Fire and Building Services No.1
Cards in this deck (40)
- 1Building control, approved documents and best practice: Regulations/acts1. Building act 1984
Imposes a duty on Local Authorities to exercise Building Control, ie, certain aspects of a building’s performance must meet a minimum predetermined standard
2. Building regulations
Rules for Building Control. Not very helpful, eg, say thinks like ‘buildings shall attain a reasonable level of thermal performance’.
Part B Fire Safety (means of warning and escape)
3. Approved Documents
Part A Structure
Part L Conservation of Fuel and Power
4. Research, Best Practice and Standards
5. Approved Document B Fire
Best practice
CIBSE
Standards (eg BS5950 Structural use of steelwork in building – Code of Practice for fire resistant design) - 2What is fire result of? What are the ingredients for fire?Fire is the result of a chemical reaction between a fuel and oxygen that results in the characteristic emission of heat and light and combustion products that we are all familiar with. In order to start a fire three key elements are required:
- Fuel (usually gaseous form)
- Oxygen
- Heat - 3What is needed to start fire? What does solid fuel do? What do liquid do?- Heat is needed to start a fire = reaction between fuel and O2.
- Solid fuels means heat breaks down material = flammable vapours which raised to a temperature to reacted with O2.
- For liquids initial heat causes change in phase. Once started heat sustains the process = fire ignited. - 4What is flashpoint? What needs to be present? How to fires start?- Lowest temperature which ignition starts with small spark/flame = flash-point.
- Fuel and oxygen already present within the building’s air
- Most fires (30%) start by electrical equipment/wiring, the rest cooking appliances, children with matches, smoker’s materials (all 10%) - 5How do fires start? What happens as temperature rises , what does it reach?- Usually start small quantities of heat and can smoulder for hours.
- Temperature rises items can liberate volatile products and reach ‘flash-point’ meaning fire quickly spreads. Temperature rises quickly so heat and toxicity of combustion are fatal with 1 breath. As combustible material is consumed, temperature drops as fire dies.
- 6What does fire have potential to do? What is function of maximum temperature? What is it determined by?- Potential a fire has to destroy a building and its contents.
- Function of maximum temperature reached in fire and the time burnt for.
- Determined by amount of fuel in the building and construction of building. - 7Why is it important how fuel release heat and how its liberated? (1/2)- Quantity of heat determined by calorific value and quantity of material = fire load which is usually expressed by woof equivalent. Buildings will contain multiple material/quantities. Ca compare different sized buildings = fire load density (total fire load / floor area).
- Rate which fire spreads determined by arrangement of fuel, which is related to size/shape of room. If contents are closely arranged a fire will spread quicker. Materials stacked to any height will burn more rapidly than those not heat and fire rises easily. - 8Why is it important how fuel release heat and how its liberated? (2/2)- Rate which fire spreads determined by arrangement of fuel, which is related to size/shape of room. If contents are closely arranged a fire will spread quicker. Materials stacked to any height will burn more rapidly than those not heat and fire rises easily.
- 9Why is the nature of the building and the way the building affects air supplied to fire and rate the building sheds heat important? (1/2)If air can reach fire through opening and results in combustion products are able to exit via same opening, heat will dissipate.
- 10Why is the nature of the building and the way the building affects air supplied to fire and rate the building sheds heat important? (2/2)Rate at which building fabric limits heat rises depends of thermal conductivity. Insulated materials can’t conduct heat of fire rapidly = glow and cause fire to spread because of radiant heat transfer. Dense materials high thermal conductivity can absorb more heat = increased period of time before fire spreads by radiant heat transfer before danger.
- 11What are the products of fire?Smoke and heat.
- 12What are smokes characteristics?- Soot obscures light resulting in poor visibility
- Combustion products are toxic - 13How does smoke affect a fire situation?At the beginning, loss of visibility is most serious. Presence of smoke causes panic meaning people behave irrationally. Coupled with the loss of sight and disorientation means evacuations difficult. Products resulting in incomplete complete combustion e.g. carbon monoxide, dioxide, ammonia etc. some only dangerous and long exposure, others such as hydrogen cyanide are lethal escape routes are necessary for good evacuation and should be free of smoke.
- 14How does heat from a fire affect structure stability and how does this affect a fifire situations? Materials?Threatens structure stability making difficult occupants to escape and hard for fire services to enter. Important components are support of the structure and those that separate the spaces. Main to materials for support are concrete/masonry and steel. When exposed to heat they behave differently.
- 15How does heat affect steel?Steel is good conductor of heat so will conduct quickly from surroundings. Above 500 Celsius steel loses strength and will fail. Small fires have temperatures between 800-1000 so steel must be covered with plasterboard, coating or cooled by water.
- 16How does heat affect concrete?Heat travels slowly in concrete so loss the strength at extreme temperatures and associated to outer layers
- 17What do steel reinforcements need?Steel reinforcements must have thick layer of protective concrete.
- 18What are the different types of passive protection?- Compartmentalisation
- Horizontal and vertical escape
- Fire resistance - 19Compartmentalisation: - What is it? - How does it help with fire safety?Limit effects of fire it is common practice to divide up the space in buildings into compartments using fire-tight walls and floors that usually have to provide between 30 to 90 minutes of fire resistance.
Limits fire loading and localises damage, reduces likelihood of occupants becoming trapped, easier for services to get in. - 20Compartmentalisation: - How do they separate the building?Compartments separate parts of building where different activities are, different occupancies, or where a given floor area is exceeded (given by Approved Document B in the Building Regulations).
- 21Horizontal and vertical escape: What is important for an effective evacuation and hw can this be done?For effective evacuation, important that the means of escape are protected from fire and smoke. This can be done by limiting distance to travel for safety (corridors and stairs) that link compartmentalised spaces, fire tight construction.
- 22Horizontal and vertical escape: Where are the weak spots in the construction?Weak spot in construction where there are doors to connect spaces they should be self closing and have minimum of 30 minutes fire resistance. Usually will have to match that of separating construction.
- 23Fire resistance: What determines building's ability to withstand fire?Ability of building construction to withstand effects of fire for specified time without loss of fire separating or load bearing function. The rating of element is dried from test carried out on sample structures which are deemed to provide appropriate fire resistance.
Common specified times are 15, 30, 60 and 90 minutes. - 24Fire resistance: What about in practice?In practice element may not provide protection promised as it depends on variables e.g. nature of the fire and the boundary conditions at junctions with other elements. Results allow simple comparisons between components to be made.
- 25Risks to passive protection: How to achieve compartmentalisation? Why must we pay special attention to these?Usual to provide services to spaces created by compartmentalisation, only achieved by passing ducts, pipes and cabling etc through fire tight construction.
Necessary to pay special attention to detailing at these points so compartmentalisation not undermined, meaning free movement of smoke and flames to other sections. - 26What are the measures to limit potential risks to integrity to the building?- Protected shafts
- Fire stopping
- Provision of protective sleeve
- Ventilation systems - 27Protected shafts: What are they? How do they reduce risk of fire spreading?Run services vertically through building from central plant room means compartmentalisation are potentially connected together. Reduce risk of fire spreading between compartments it is desirable to use a protected shaft to contain the main vertical service runs.
- 28Protected shafts: What are they built from? What must be protected?Built using fire resisting construction similar to escape staircases, any access door/covers must meet requirements/
Sometimes drainage and water supply pipes must be protected in enclosure providing a minimum of 30 minutes fire protection. - 29Protected shafts: In case of 30mins protection? What does enclosure reduce?In this case integrity of compartments is maintained, pipes being sealed at compartment walls and floors. Enclosure reduces likelihood of flames burning away at pipework and passing between compartments
- 30Fire stopping: What is it? What is achieved?When pipes/ducts pass through compartment all or floor, important that whole provided is small as possible and gaps are properly sealed/fire stopped.
Achieved by using intumescent mastics, cement mortar, plaster, glass fibre, etc. - 31Fire stopping: What is the correct choice dependent on? What is the general requirement?Correct choice dependent on materials pipe/duct and separating element are made, allow for thermal movement.
In addition to general requirement the number of pipes permitted to pass through compartment wall/floor be kept minimum, limits placed on their size as well. - 32Fire stopping: What do restriction on pipe size limit?Temperatures commonly encountered in fires, materials such as steel and iron soften an fracture so permit free passage smoke, restriction on pipe sizes is meant to limit this all.
- 33Provision of protective sleeve: What is this?Alternative to restricting pipe size it’s possible to use cast-iron all steel pipe as sleeving to a less resistant pipe such as PVC, aluminium alloy etc.
- 34Ventilation systems: Documents- BS 5588: Fire precautions in the design, construction and use of buildings: Part 9 Code of
practice for ventilation and air conditioning ductwork.]
- BS 5720: Mechanical ventilation and air conditioning in buildings] - 35Ventilation systems: Why do ducts present danger?Ducts present threat to integrity of fire resistant compartments and as a result offer a convenient path of smoke an flames. Can pose threat to safe evacuations of occupants. As smoke can spread rapidly through all spaces served by the system.
- 36Ventilation systems: What are the common approaches to minimise risk to ventilation system?- Fire dampers
- Smoke detectors
- Self-supporting fire resisting enclosures
- Dire protected ductwork - 37Ventilation systems: What are fire dampers? Why are they used?When will they start working?Fire dampers used to close sections of duct in event of fire and may be actuated By temperature sensor/smoke sensor. Smoke represents potential issue with temperature dampers as during initial stages of fire, combustion products can be relatively cool. Dampers will not operate until flow attains temperature around 75 Celsius meaning large areas of building May be affected by smoke. Important to you smoke detector in addition.
- 38Ventilation systems: What are smoke detectors? Where are they placed?Smoke detectors positioned in compartment but can be placed in ducting itself. Where ductwork unprotected, fire dampers are placed at points were system penetrates compartment walls/floors.
- 39Ventilation systems: What are Self-supporting fire resisting enclosures? How do they work?Self-supporting fire resisting enclosures or protected shafts, work is run through shafts that possesses same fire resistance as components in building, fire dampers provided by ducts leave protected shaft.
- 40Ventilation systems: What is a fire protected ductwork?What else is provided?Fire protected ductwork, duct itself forms protected shaft through application of protective material or by virtue of material from it is constructed. Important that this form of duct has same fire resistance as construction of compartment. Fire dampers must be provided and are positioned at terminal units and where any unprotected duct connects to system.
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- Architectural Engineering Flashcards on Fire and Building Services No.1, created by Alice K on 22/10/2019.
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