Example questions 1 Flashcards
Describe the fire tetrahedron and explain the implications for extinguishing fire
Possible Marks = 4
The fire tetrahedron is made up of the following elements.
Heat
Fuel
Oxygen
Which make up the fire triangle
4. Chemical chain reaction (exothermic)
Fire can be extinguished by removing or controlling one or more of the parts of the fire tetrahedron
Heat can be removed or reduced by using water to cool the fire
Fuel can be removed by taking away the fuel source e.g. turning off a gas supply
Oxygen can be removed or reduced by smothering. e.g. placing a fire blanket over a fire
All three elements of the fire triangle (Heat, Oxygen, Fuel) must be in balance, removal of one of the elements described above will interrupt the chemical chain reaction (exothermic) which sustains the fire process.
Describe the five stages through which a fire progresses and explain the role of passive fire protection at each stage
Ignition
Growth
Flashover
Fully developed
Decay
Ignition. Passive systems are included in the buildings construction that do not readily ignite and propagate flame. These products and systems will reduce the ability of a fire to develop into something larger, as well as reducing the ability of fire to pass around the internal surfaces of the building
Growth. Passive fire protection products and systems are usually made of materials that are non combustible or of limited combustibility which limits the fire load and available fuel. They also protect escape routes in order to allow safe evacuation of the buildings occupants.
Flashover. At this point (approx. 600degC) all combustible materials in the fire compartment will become involved. Passive fire protection systems now begin to resist the passage of fire from the compartment of origin into other parts of the building and insulate the structure against the effects of fire. Protected escape routes are maintained to allow for evacuation of occupants and to protect fire fighters should they need to enter the building.
Fully developed. Passive fire protection systems that have been tested and assessed to provide fire resistance to the specified period of time, contain fire in an effort to keep it as small as possible and limit fire spread. They also insulate the structure to maintain its stability/load bearing capacity and prevent collapse.
Decay. As the fire decays either as the result of intervention by fire fighters or it has consumed all the fuel that is available, areas may reignite particularly in unseen cavities. Passive fire protection materials and systems are less likely to do this, as they are usually none combustible or of limited combustibility, some passive fire protection systems can continue to provide protection to the structure beyond the designed fire resistance period.
- In relation to means of escape, define the following terms:
A) Place of reasonable safety
B) Travel distance
(4 marks)
Place of reasonable safety
A place within a building or structure where, for a limited period of time, occupants will have some protection from the effects of fire.
Usually a corridor or stairway and will normally have a minimum of 30 minutes fire resistance
Will allow occupants to continue their escape to a place of complete safety
Travel Distance
Actual distance to be travelled by occupants from any point within a building to the nearest or final exit
- Internal compartmentation and fire resisting construction are examples of passive fire protection.
A) Explain why these components are described as passive fire protection. (2 marks)
A) passive fire protection is “built in “ to the fabric of a building to provide fire resistance and insulate against the effects of fire, and/or contain fire within the compartment of origin
Passive fire protection systems do not require activation in order to carry out their function.
- Describe the content of a fire test report.
Possible marks = 2
7 possible points
A fire test report is a scientific type document that describes:
1.Test specimen
- Test standard
- Installation of test sample
- Detailed measurements of the test sample performance
- Detailed measurements of the furnace pressures and temperature regime
- Results of the test
- Observations throughout the test
- Explain the limitations of a fire test report
Possible marks = 2
Limitations of such a report:
Only relates to the sample tested, without variation
Scientific language and presentation of data makes the report difficult to understand/interpret
Test regime is not representative of a real fire scenario, only a standard fire test curve
May not be to an internationally recognised test standard (e.g. they could be Ad Hoc)
There may be little or no control over the selection of test standards (BS regime)
- Describe steps that building managers can take to ensure that fire protection provisions in their premises are maintained
Monitoring of activities that might affect fire protection measures e.g. maintenance and changes to the building fabric
Inspection of compartmentation particularly when building works are required.
Ensure all materials used have appropriate certification
Ensure all building works are carried out by competent/qualified companies and individuals
Ensure tenants are aware of fire evacuation procedures
Ensure appropriate fire drills are carried out
Ensure policy documents and manuals are in place and up to date
Maintain all fire protection systems and keep appropriate records
Provide and maintain adequate signage
- Identify 3 types of sprinkler system and outline a typical building/situation where each one would be installed.
(6 marks)
Wet pipe
No risk of freezing, quick to operate and required for multi storey/high rise buildings
Alternate
As the name suggests, they are full of water in the summer months but are drained in the winter and charged with air under pressure to avoid the risk of freezing. Used in buildings that are not heated e.g. warehouses
Dry Pipe
Used in buildings where freezing temperatures my be an issue. Will provide the coverage needed without the risk of bursts. Pipes are filled with air at all times, on activation the sprinkler head opens and the resulting change in pressure activates a release valve which then opens to allow water to flow into the system
Other measures could be..
Pre action.similar to dry pipe but water flow is activated by a heat/smoke detector
Deluge: Not strictly a sprinkler system. Designed to quickly extinguish a fire in a are of high risk. Usually in confined areas.
- Some passive fire protection systems depend on the operation of appropriate fire and smoke alarm systems to fulfil their intended role. Identify and describe three such systems.
(6 marks)
Automatic door hold open/closure devices
Designed to hold open self closing fire doors or allow them to swing freely during normal use when activated by the fire alarm the door is released and closes to maintain the fire compartment. Particularly useful in areas of high traffic such as corridors.
Smoke control damper
Installed in smoke extraction ductwork in the line of the separating element, activated in the event of a fire incident to control the extraction of smoke from the effected compartment and direct the smoke from the building.
Active fire barriers
On detection of fire by an alarm system the active fire barrier is deployed in order to maintain compartmentation and/or protect a means of escape. Such fire barriers are usually out of sight during normal conditions giving flexibility to designers in open plan areas.
- Explain two different ways of flame retarding timber.
(6 marks)
Surface preparations.
Intumescent coatings applied to the surface that react to heat to form an insulating layer or “char”. By blocking heat and oxygen they limit the level of combustion and surface spread of flame.
Impregnations
Usually offsite/factory based treatments that are designed to drive the flame retardant into the timber often involving vacuum or pressurised application techniques. Impregnations can improve the surface spread of flame and general “reaction to fire” performance. Timber should not be machined, planed or sanded once the treatment has been added as this will remove the protection that is in the surface layer of the timber.
- Describe the factors that effect the loadbearing capacity of the following building support systems in fire.
Concrete.
Concrete.
When exposed to high temperatures concrete structures may suffer from “Spalling” which is the process by which pieces of concrete break away under the pressure exerted as the trapped/bound water within the concrete turns to steam. Prolonged exposure to sever fires such as those experienced in tunnels may cause significant loss of concrete and expose reinforcing steel increasing the risk of structural collapse.
- Describe the factors that effect the loadbearing capacity of the following building support systems in fire.
Timber.
Timber.
Timber is know to have a measurable rate of char and this is used in order to design buildings that in most cases satisfy fire resistance requirements. The size and type of timber will dictate the level of resistance to fire of a timber element. In some circumstances timber structures can be further protected by the addition of appropriately fire tested products and systems
- Describe the factors that effect the loadbearing capacity of the following building support systems in fire.
Structural steel.
Structural steel.
Temperature: Historically seen as 550 deg C at which a loadbearing steel beam or column will typically be capable of supporting around 40% of the maximum design load.
Load: which will be dependent on the buildings design and intended use. The more load a steel element has to carry the lower the temperature at which it will begin to collapse.
Shape: the shape of a steel profile will have an effect on its ability to withstand heat. E.g Cellular beams tend to fail at lower temperatures and within the web, I& H sections usually fail in bending.
- Explain how intumescent coatings work and how they can contribute to the load bearing capacity of steel frames.
“Intumesce” means to swell. Intumescent coatings, also known as reactive coatings swell under the influence of heat to form an insulating layer or char. It is this char that provides the insulation to the steel section and keeps its temperature below the critical level.
Intumescent coatings are applied to primed steel, usually via airless spray to the required thickness as declared in the test/assessment data. On exposure to fire they expand to form the required level of insulation
Typically a thin film intumescent coating will expand to around 50 times its original dry film thickness (DFT)
Intumescent coatings are tested and assessed through standard fire resistance test regimes. The resulting assessment will provide the end user with a required thickness per steel section as dictated by the section factor expressed as A/V where A = the Area of a steel section that is exposed to fire and V = the Volume of a section, or the cross sectional area, per unit length. This thickness of coating should then be applied in order to achieve the specified period of fire resistance
- A) Explain the difference between box, profile and solid application of fire protection to steel
(2 marks)
A
Box- usually a board application forming a 3 or 4 sided encasement around a steel section. Section factor (A/V) will be lower as a result as of the reduced surface area (A) when compared to profiled applications. The ability to pass services through holes in the web will usually be lost as a result. Spray applied none reactive coatings can also be applied in a box configuration by using mesh or lath secured between the flange tips of an I or H section.
Profile- products and systems are installed following the shape of the steel section. Usually this is done with coatings but boards can be cut and installed to follow the profile. Section factor will be higher than an equivalent boxed application due to the increased surface area exposed to the fire when compared to boxed applications. (see above)
Solid – is a method of installing non reactive coatings in a way that fully fills the space between flanges
B)Describe the role of fire resistant boardings when protecting structural steel sections
(2 marks)
B
Boards are fixed to steel beams and columns in order to insulate them from the high temperatures generated in fire. Fixing methods can vary even for the same product, all installations should be in line with the manufacturers published instructions.
C) Describe two different types of materials used in the manufacture of fire resistant boards.
(2 marks)
C
Man made mineral wool (stone wool) – lightweight panels usually used on beams as they are soft and easily damaged
Calcium silicate- medium density products which are mechanically fixed around beams and columns where a higher level of durability is required. They are generally more able to deal with longer periods of fire resistance
Could also include gypsum based products (reinforced or not), Vermiculite boards, Ceramic blankets, Magnesium Oxide
- State and explain the three main criteria that materials/systems are assessed against when undergoing fire resistance testing to BS476.
REI
Stability (Load bearing Capacity) (R)
Integrity (E)
Insulation (I)
Stability (Load bearing capacity)is the ability of a material/structure to withstand the forces present in a fire and maintain its capability to support its designed load for the period of fire resistance.
Integrity is the ability of a material/structure to withstand fire exposure without cracking or gaps opening up to allow passage of hot gases, smoke and flames through to the non fire side
Insulation is the ability of a material/structure to limit heat transfer during exposure to fire. In the case of structural steel, materials/systems are required to keep the temperature of a beam or column below its critical temperature for the fire resistance period. In the case of compartment walls and floors, fire resistant structures must maintain temperatures on the non fire side such that they do not rise more than and average of 140 DegC above ambient, or above 180DegC at any one point.
- What are the two main purposes of compartment walls and floors?
Prevent fire spread by containing it in the compartment of origin in order to protect escaping occupants and maintain a safe means of escape and/or protect fire and rescue personnel.
Prevent small fires becoming large, on the basis that large fires are more dangerous than small ones to occupants, fire and rescue personnel, and people in the vicinity of the building
- Generally, fire resistant glazing falls within three tested classifications. Explain how each of the classifications are identified and how they differ from each other. (6 marks)
E. Integrity only glazing systems.
EW. Integrity with limited heat radiation capability
EI. Integrity and insulation
E. designed to resist the passage of fire and smoke from the compartment of origin for the specified period of fire resistance
EW. Provides integrity to the same extent as E but has additional, limited resistance to heat transfer to below 15kW/m2 on the unexposed side. Not currently recognised in the UK, but used elsewhere in Europe and the wider world to protect means of escape for a limited period of time in order to protect those evacuating a building.
EI. Provides integrity as per E but also full insulation to prevent heat transfer to the non fire side, such that the average temperature increase is limited to an average rise above ambient of 140degC or a maximum of 180degC
- Explain the difference in design and operation of curtain fire dampers and intumescent fire dampers.
Curtain Fire Dampers:
Constructed of a series of interlocking, metal blades which fold into the top of the damper assembly and hold it open in general use.
Released by either a thermally activated or fusible link in the event of fire, normally designed to activate at 72 degC +/-4 degC which allows the blades to descend closing off the space within the duct and sealing it against the passage of fire and smoke.
Separate fire resistance test evidence is required to support horizontal and vertical installations
Damper should be installed in the line of the separating element (wall or floor)
Intumescent Fire Dampers:
Incorporate components that expand in the event of fire to close off the space within the duct to prevent the passage of fire and hot smoke. If a cold smoke seal is required the intumescent damper cannot provide this on its own, an electro- mechanical device that is activated by a smoke sensor or a fire alarm must be fitted in this instance.
Damper should be installed in the line of the separating element (wall or floor)
- Ventilation ductwork offers little or no protection against fire spread. Explain three ways of maintaining the fire resistance of walls and floors penetrated by ductwork.
Possible marks = 8
Method 1. Protection using fire dampers
Method 2. Protection using fire resistant enclosures
Method 3. Protection using fire resisting ductwork
Method 1: dampers are placed in the plane of the compartment wall or floor which are activated in the event of fire via either a fusible link which releases the damper under the influence of heat from the fire, or a mechanical damper which is released automatically on activation of a fire alarm or detector, closing the internal space within the ductwork and maintaining the fire compartment.
Method 2: Ductwork is enclosed in fire resistant construction such as a shaft or riser. Fire protection to the ductwork system is provided by the enclosure, compartmentation is maintained by fire stopping at walls and floor penetrations using appropriately tested and approved systems.
Method 3: Ductwork is constructed from materials that provide the necessary fire resistance. This can be metal ducts which are coated with fire resisting materials such as paints or boards. Or the ductwork itself can be constructed from fire resisting boards. The fire resisting ductworks fire performance should be demonstrated by appropriate and valid fire test evidence ideally supported by 3rd party certification of both the ductwork system and the installation company. Appropriately tested fire stopping solutions should be used where the ductwork passes through compartment walls and floors paying particular attention to smoke control requirements and the necessary support of the duct, and the firestopping required at the point where the duct passes through the separating element.
- Identify five different situations where fire stopping would be needed and describe an appropriate solution.
(10 marks)
Penetration seals: required where services pass through a separating element (wall or floor)
Example: batt and mastic system incorporating appropriate pipe closures where plastic pipes pass through a compartment wall.
Linear Joint seals: required between fire resisting elements e.g. the junction between a floor and a wall.
Example: elastomeric expansion joint strip installed at the appropriate depth and width for the designed fire resistance period.
Small Cavity Barrier: Usually installed between two leaves of masonry to prevent the passage of fire in the unseen/inaccessible space
Large Cavity Barrier: Used to subdivide the space in a roof void or beneath a raised access floor.
Temporary/removable penetration seal: Installed to maintain compartmentation but can be easily removed in order to install more services.
Example: at the compartment wall beneath a raised floor in an office building where data cables are frequently added or changed. Often provided by the use of fire resistant bags/pillows.
- Explain the purpose, construction and design of a fire barrier system and how they differ from cavity barriers. (6 marks)
Fire barrier systems are a fire stopping element intend to continue the line of a fire compartment
They have the same fire resistance as the compartment wall or floor into which they are installed. (integrity and Insulation)
Cavity barriers are used to subdivide the space within a compartment and as a result they do not need to have the same level of insulation performance as a fire barrier. UK guidance currently requires that they provide minimum 15 minutes insulation
Cavity barriers can be large or small
Small: typically to seal the space between two leaves of masonry to prevent passage of fire and smoke within the unseen space
Large: typically used to subdivide the space within a roof structure
- State 6 components of a fire doorset or assembly and explain their role in maintaining fire performance
Possible marks = 6
Door leaf: The main component of a fire door set or assembly, used as a means of access through a fire compartment wall during normal use. Must provide a barrier against the passage of fire. Fire resistance is usually 30 or 60 minutes Integrity, higher periods of fire resistance can be achieved.
Intumescent strips: Installed in the long edges and top edge of the leaf or frame. Expand under heat to seal the space between door leaf and frame to prevent passage of fire and hot smoke.
Smoke Seals: Installed around the edges of the door leaf to prevent passage of cold smoke. Can be brush or blade type
Hold open/closure device: usually fitted to the head of the door frame/leaf. Designed to hold the door in the open position in normal use. Closes to maintain fire integrity of the compartment wall on activation of a fire/smoke alarm.
Glazed panels: installed in the door or surrounding framework to allow visual assessment of the area beyond the door during normal usage. Must provide the same level of fire resistance as the rest of the door during a fire scenario. The glazed aperture will consist of the glass panel, and all the fixing details that make up the glazed assembly. Beading, sealant, glazing setting blocks, fixings are all important to the fire performance of the glazing panel.
Hinges: Normally 3 in number. Should be sufficient to support the weight and usage requirements of the door in normal use as well as in fire. All hinges should carry a CE mark as evidence of fitness for use. Usually have an intumescent pad or sealant between the back of the hinge plate and the door/doorframe to control passage of heat.
- Explain the design, purpose and operation of a fire shutter.
(6 marks)
Usually constructed from multiple leaves of metal which are secured in position above an opening in a compartment wall or floor or in the structure around a shaft.
The shutter should provide the same fire resistance as the separating element into which it is installed
Usually fitted with a thermally activated self closing device or fusible link that under the effect of heat from a fire activates the closing mechanism in order to maintain the fire resistance of the separating element.
Can be connected to an alarm system or detection device which when activated would close the shutter
Should default to the closed position in the event of a power failure or similar
Should be designed and constructed such that the descent of the shutter is controlled
If the shutter represents more than 25% of the overall area of the separating element it should provide full insulation. E.g. It should insulate the non fire side such that temperatures do not increase more than an average of 140 deg C or a maximum of 180 deg C
In relation to fire resistance, explain the difference between “insulation” and “integrity”. (4 marks)
Integrity - The ability of the structure to maintain its fire integrity to ensure that no gaps of sufficient size open up which allow penetration of hot gases, smoke and flames between one fire compartment and another.
Insulation – Insulation is the ability to protect the unexposed face of a compartment, i.e. the other side of a compartment wall to where the fire is burning, should not increase in temperature above an average of 140°C or by more than 180°C at any one point.
One of the measures used in assessing the way in which a material will react to fire is the extent to which it is combustible. Identify three other factors that can be used in measuring how a material reacts to fire. (3 marks)
Spread flame (over their surface)
Release heat (rate of/fire propagation)
Produce flaming droplets and smoke (not used in UK regulations)
Ignitability
Explain the issues and limitations that need to be taken into consideration when interpreting fire testing and assessments. (4 marks)
- First-party certification Where an individual or organization provides goods or services with an offer of assurance that they meet certain claims.
- Second-party certification An association to which the individual or organization belongs provides some assurance by virtue of membership.
- Third-party certification An independent assessment is undertaken by a Certification Body, themselves accredited by the United Kingdom Accreditation Service (UKAS in the UK), declaring that specified requirements pertaining to a product, person, process or management system have been met.
The limitations of testing and assessments is that they can be ad hoc and may not be internationally recognised.
Tests are carried out in a controlled environment and is therefore not a true reflection of a real-life scenario.
Scientific language make the test difficult to understand.
Only relates to the standard sample tested without variation.
Those making the assessments need to be competent and be able to demonstrate this competency.
Fire test reports are often used to demonstrate a product’s fire performance. However, fire test reports are only applicable to the product or construction as tested with only limited variations permitted in the direct field of application of the particular test method. Further, they have none of the quality control aspects of third-party certification.
Finally, fire test reports are often long and complicated documents which are not suitable for marketing purposes or for use by authorities having jurisdiction such as building control.
Passive fire protections measures should be taken into account when developing plans for building projects. One reason for this is to ensure that the correct checks are carried out at the right times. Identify and explain two other reasons. (4 marks)
Passive fire protection is installed in the correct order, preventing unnecessary rework later which, in turn, may lead to an unsatisfactory ad-hoc solution being applied.
Fire stopping systems installed then IT knock holes through the compliant walls. By placing this work with specialists, and with careful programming, it is much more likely that the correct materials will be specified and installed, avoiding damage and rework.
Attempting to inspect and remedy deficient Passive Fire Protection at a late stage will prove extremely challenging and/or time consuming, since passive fire protection is often hidden or inaccessible once the building is complete.
It will also prove to be far more expensive than installing it correctly first time.
Contractors are required to provide certificates of conformity to demonstrate compliance with relevant regulations.
a) Explain what is meant by the term “active fire protection” and state how active fire protection differs from passive fire protection. (3 marks)
Active fire protection is a form of protection measure that requires special energization or a command signal to operate. Passive fire protection is in built within the structure and doesn’t require activation to complete its role.
b) Identify and describe two types of smoke detection system. (4 marks)
Optical Smoke Detectors – One of the most common form of smoke detectors and usually found in most domestic premises. This type of detector works on the principle of light. Using infrared, the detector detects smoke when the particles block light from reaching the sensor chamber.
Smoke Aspiration System – This system is extremely sensitive and monitors air quality by drawing air into a network of small pipes. These pipes then lead to a sampling chamber where a laser is used to detect the presence of smoke particles.
Identify five locations in a building where emergency lighting should be located. (5 marks)
9 possible answers
- Each final exit door
- Escape routes
- Intersection of corridors (changes in direction)
- Outside each final exit and on external escape routes
- Emergency escape signs
- Stairways so that each flight receives adequate light
- Changes in floor level
- Windowless rooms and toilet accommodation
- Fire-fighting equipment
Describe the insulating materials that can be used to protect structural timber and state the factors that affect the required thickness of the protective layer. (4 marks)
Exposed timber sections can be designed with additional ‘sacrificial’ timber to a section, so that the part exposed to fire can protect the inner material from fire damage while the outer part chars at a slow, predictable rate. Where this is not the case, structural elements, including mechanical fasteners, can be insulated from heat by covering them with one or more layers of fire resisting insulating material, for example gypsum plasterboard or a calcium silicate board, of a specified thickness. The thickness of the fire protective layer will be governed by the density and makeup of the structural element, e.g. solid timber, glulam, Laminated Veneer Lumber (LVL) etc
a) Explain why the thickness of a steel structure needs to be considered when planning for appropriate fire resistance. (2 marks)
The thicker and heavier a steel section becomes the longer it will take to heat up, therefore the amount of structural fire protection required to control the steel temperature to below the critical level will be less than would be required for a thin lightweight section. Fires in buildings regularly exceed 1000°C within a relatively short period of time (30 – 60 minutes), yet heavily loaded steel loses its design margin of safety, (about 40%) at temperatures around 550°C regardless of the grade, and as its temperature rises further the loss of strength is rapid and significant.
b) State and explain the “section factor” formula used when determining the length of fire resistance. (3 marks)
The length of fire resistance period is calculated based on the size and weight of the steel section using a formula known as the ‘Section Factor’ (A/V) where:
* A = Surface area of steel exposed to the fire per unit of length
* V = Volume of the section per unit length
In the past A/V has also been described as Hp/A (heated perimeter of the exposed cross section divided by the total cross-sectional area).
a) State three advantages of applying intumescent coatings off-site. (3 marks)
Provides better quality control in terms of temperature and humidity.
Provides better quality control in both wet film as well as dry film readings.
No disruptions to other trades operating on site.
No risk to area due to overspray.
b) State two challenges that can arise when intumescent coatings are applied off-site. (2 marks)
- Workshop handling and the transportation of steel members to the construction site must be done with care or risk damaging the paint.
- Possibly higher transportation costs.
- If the paint is damaged during transportation or installation, the applicators must re-apply it on site.
Identify two different types of fire resisting floors and explain how each of them may be constructed in order to achieve the required fire resistance. (6 marks)
Fire-resisting floors may generally be considered under three primary types:
Timber joist floors
Timber joist floors will char above certain temperatures, the wood will be progressively but predictably consumed by fire. The timber thickness is critical to the structural performance in fire and therefore must be correctly specified. Timber char rate may typically range from 0.5 - 0.8 mm / minute. Fire resistance is usually afforded by a combination of protection to the underside and ensuring there is enough sacrificial timber in the joists. Underside protection will normally be provided by fire resistant board systems such as plasterboard or similar but other systems are available.
Concrete floors
Concrete floors contain entrapped moisture. They may well be reinforced with steel. In fire, the entrapped moisture will heat up and turn to steam. The steam pressure will increase and try to find relief by escaping from the concrete. The escape mechanism can be violent and large pieces of concrete may become detached by explosive spalling. Any steel reinforcement in the concrete will be initially protected by the concrete, until spalling exposes the steel and it will substantially expand to threaten the viability of use as a floor. The extent of concrete cover over reinforcement is therefore critical to the fire resistance available and must be correctly specified.
Composite floors
Composite floors generally consist of a profiled metal deck with a poured concrete topping which can perform differently in fire, because the metal base will conduct heat from fire laterally, and in so doing the metal face will attempt to expand. The rate of temperature increase in the critical parts of the floor may be lessened compared to concrete alone, however the composite floor will also be fixed through shear connectors to the supporting steel structure. During the fire, steam formed in the concrete may force out the metal decking, distorting it and causing gaps and subsequent failure, and whilst the steel reinforcement will transfer the load and the heat from fire, the composite structure may ultimately deform under the heat and sag under the load of the concrete.
The fire performance of all floors can be enhanced through the use of added passive fire protection systems, appropriate to the floor type.
These passive fire protection systems act to insulate the timber, concrete, or steel from the effects of fire for given periods of time. The protecting mechanism depends on the characteristics of the PFP system and careful design based on fire test evidence is essential. Manufacturers’ test evidence must be understood and incorporated into the specification to ensure that the anticipated performance is achieved. The choice of passive fire protection can also be important if the performance is not to be negated by deformation of the floor system. Some PFP materials will deform less well than others, which may lead to fracture under deformation in fire.
Describe the considerations to be taken into account when selecting an active fire curtain for installation. (5 marks)
Active fire curtain barriers are normally used to provide compartmentation and to protect means of escape and may be installed in any type of building where these are required.
The following should be considered when looking to install an active fire curtain:
1. What level of fire resistance is required
2. Its intended purpose, provide compartmentation or to protect means of escape.
- The overall size of the curtain
- How it will be operated
- How many motors are required to operate it
- Whether or not vertical channels are required.
- Ensure the curtain fails safe using gravity
- Ensure there is a compliant alarm system that will be used to trigger the activation of the curtain
State the performance requirements of a fire resisting suspended ceiling. (3 marks)
Not break or collapse during the early stages of a fire when evacuation and rescue operations can still be carried out.
Prevent surface spread of flame
Provide a period of fire resistance to protect the services that are likely running above the ceiling.
Stop fire passing through them either by flames or by heat conduction.
Describe the situations where each of the following would be used to achieve fire stopping and give two examples of the fire stopping products that would be used:
a) penetration seals (4 marks)
a) Where services pass through fire separating elements and/or compartment walls or floors. For example a non combustible pipe penetrating through a wall or a cable penetration.
Stone wool products for fire-stopping are supplied in a number of forms; typically referred to as mats, batts, or pre-formed shapes.
Ablative coated stone wool batts/board, the ablative coating acts as a sacrificial layer designed to absorb/consume heat from a fire and release it in the form of a gas, to protect the underlining stone wool slab.
Sealant or mastic (for example silicone, acrylic) applied by a mastic gun or trowel applied into an opening and between/around suitable penetrating services.
Describe the situations where each of the following would be used to achieve fire stopping and give two examples of the fire stopping products that would be used:
b) linear joint seals (4 marks)
b)Also known as Pre-formed elastomeric seals. Typically installed between fire resisting elements of building construction, for example the junction between a wall and a floor.
These are made from elastomeric foam sometimes encasing stone wool, and sometimes with reinforcing sheets on either side. The foam and/or the reinforcing sheets may be intumescent. These products are generally supplied in a strip form.
Sealant or mastic can also be used for linear joint seals. When used in linear joints where movement is expected, a sealant with the ability to accommodate the movement of the joint should be used so that a seal is maintained in service and during fire conditions.
One method of fire stopping is bags/pillows. a) Describe this method of fire stopping and explain the installation process. (4 marks)
Bags/pillows or cushions are available in various sizes and shapes and are specified for use in temporary or permanent fire-stopping situations where services such as cables pass through walls and floors. Bags/pillows are made from non-combustible fabrics and enclose a filling material which may incorporate an intumescent material. FRICTION FIT!!!
Bags/pillows must be placed into the opening(s) using the correct orientation, packing density and overlap (staggered joints), to achieve the desired fire resistance. For wall penetrations, bags/pillows are normally self-supporting, but large openings with few penetrating services may require a steel retaining mesh for support on both sides of the penetration.
