BYTNAR - TALKS
EPISODE 016 - APPROVED DOCUMENT B - FIRE SAFETY - PART 3 OF 4
This episode is for people who want to know more about Approved Document Part B – Fire Safety.
You should like this episode if you ask yourself questions like:
What are the requirements for maintaining a building's structural stability during a fire under Approved Document B?
How does compartmentation work to prevent fire spread in dwelling houses and between separate structures like garages?
What fire resistance standards must structural elements of new additions to existing buildings meet?
Why are sprinkler systems required for certain flats, and at what height does this regulation apply?
What measures are necessary to inhibit unseen fire spread within cavities and concealed spaces in flats?
How should openings and penetrations in fire-resistant compartments be protected to prevent fire and smoke spread?
What are the criteria for external walls and roofs to resist fire spread between buildings, and how does distance to the boundary affect this?
How should fire spread over roof coverings be managed, and what are the European directives related to this?
What guidelines does Approved Document B provide for determining unprotected wall areas based on proximity to property boundaries?
This is Bytnar Talks the Engineer Takes on Construction Episode 16 hi I'm Piotr Bytnar each day I help my clients plan and design building projects through Bytnar Limited a Consulting Chartered Structural Engineers practice my biggest passion and the corner stone on which I've built my business is find finding clever solutions for construction projects I am a chartered structural engineer and a bing software developer so you can rest assured that I will strive to talk about the best practices and the use of new technologies in the industry and if you're embarking on a construction project or are involved in planning designing and building the world around us you'll find this podcast useful approved document B fires safety part three here we go again welcome back to the bitnar talks your favorite podcast on all matters of architecture engineering and construction it is Thursday the 16th of May 20124 and I'm here back with you with the 16th episode and further information on fire safety fire safety is the meal well served cold and and in a testing menu fashion so you can can appreciate its flavors more therefore I split it into several episodes last week in episode 15 I close section two three and four talking about the Escape Route of dwelling houses and floods as well as the internal fire spread through Linings approved document B provides detailed guidelines for means of Escape in dwelling houses and flats section two m sizes direct exits for ground flows and protected stairways for higher levels with specific criteria for escape windows and doors section three focuses on containment within flats and controlled evacuation highlighting separation of living and sleeping areas and regulated evacuation distances section four requirement B2 addresses internal fire spread mandating material f for Linings to resist flame spread and heat release particularly scrutinizing insulated panels and thermoplastic materials for fire resistance and applications and of its application location suitability now I'll carry on to cover the requirement B3 and B4 so internal fire spread structure and external fire spread section five all the way to to section 12 so without further Ado let's dive into the fire safety requirements B3 and B4 as treated in the approved [Music] document the requirement B3 and B4 deals with the fire spread taken in consideration structure and external fire spread in the sections 5 to 12 in this episode you'll find out what to take in consideration and when considering comp compartmentalization cavity breaking fire stopping and more as well as how distances of the buildings to building to another building matters in light of the fire spread between them so without further Ado let's get on to it generally speaking before we get to the interpretation and guidance of approved document let's have a look what does the regulation actually requires of us so in the document internal fire spread structure requirement B3 there are four points to consider point one the building shall be designed and constructed so that in the event of fire its stability will be maintained for a reasonable period point two a well common a wall common to two or more buildings shall be designed and constructed so that it adequately resists the spread of fire between those buildings for the purposes of this subparagraph a house in the Terrace and a semi Dage house are each to be treated as a separate building point three were reasonably necessary to inhibit the spread of Fire Within the building measures shall be taken to an extent appropriate to the size and intended use of the building comprises comprising either or both of the following subdivision of the building with fire resistant construction or and installation of suitably suitable automatic fire suppression systems and point four the building shall be designed and constructed so that the Unseen spread of fire and smoke within concealed spaces in its structure and fabric is inhibited so simples separate buildings should be isolated from each other that's a no-brainer right separating meaning fire spread so in the event of fire its structure is to survive reasonably long within building spaces should be either or both compartmented and protected by sprinklers and the concealed spaces restricting the spread of Fire Within them can we go home now you ask you can if you do not want to know more and to find the same language with your building control officer as they will certainly refer to the below sections so starting with Section Five of requirement B3 internal fire spread IND dwellings when we start thinking about the required protection we ought to go to a p B of the approved document to assign the required protection time to given situation generally speaking 30 to 120 minute resistance for the maximum fire scenario protection toward regulator cause elements of structure in the way the fire should be able to reach its full potential and declin without collapsing the building naturally such consideration may be reasonably relaxed for building of low consequences which collapse would not endanger buildings and people in close vicinity and that concerns all the structural elements of the building frames floors walls buttresses beams roofs and on and on so what is considered not an element of structure it's all elements that do not form part of load bearing or stability system of the building or Escape Route but also the lowest floor of the building where we add an additional story to the two-story house the new story needs to be Ray 30ir as need all floors forming the part of the existing Escape Route the existing first floow structure should to be of sufficient structural capacity but some relaxation on integrity and insulation of fire is fine in the event of fire the first flow should be no less than R30 if the extension is sufficiently small Only One More Story up to two rooms of less than 50 m squares in total compartmentation is important to avoid spread of fire between separate houses like in case of terrce or semi Dage properties but also between the houses and the garage garage should be made in the way that if there is a door accessing the house directly from it there is no way of fuel to get into the house so think slopping away from the doors and those raised minimum 100 millimet over the garage floor for compartments to be effective they need to form a complete barrier so need to be considered together with other DET of elements attached to them all them attached to these elements like the party wall under the roof or with a fire barer in the form of a parid wall any penetrations of compartment should be as small as possible and Fire Stop topped and structurally isolated so for example roofs adjacent to compartments should be B should be of the type B roof T4 classification on a A2 S3 D2 substrate for at least 1 and 1/2 M each side of the boundary line and that would exclude thermoplastic windows from the zone some continuity of roofing patterns or substrate of limited contribution to fire over the compartment wall can be allowed in buildings up to 50 m in height but what what what all of those abbreviation mean really what does it mean so B roof T4 is the type of the roof tested to to the method T4 okay so we'll do all of those abbreviation means so B roof T4 is that highest performance classification for for the roof it means the roof is B roof class that's been tested to type of the test which which is T4 type of the test test that is used to determine classification of the roof it measures the external fire exposure resistance of the roof the flame penetration and spread of the Flames meaning this roof will resist flame penetration for 60 minutes and extinguish within 5 5 minutes of removing the heat Source not creating more fire spread than 0.38 M across the region of burning so basically means 1.9 19 CM either side and A2 S3 D2 for example a board of A2 very limited combustibility but may produce a lot of smoke or droplets I've explained that a little bit more in the previous episode so if you like to if you like to listen to that you more than welcome more than invited the next ever so important aspect of fireproofing are cavities of buildings cavity can allow the fire to spread unnoticed and interestingly due to the chimney effect a that spread at which at at the speed at which such spread takes place place to address the issue we introduce cavity barriers in sent points of our buildings between the compartments making sure the cavity is not a bridge between compartments but if the construction is of a typical cavity wall construction it is sufficient to close the space around the openings and top of walls with any material or not at all in case of full fill insulation otherwise cavities need to be at least I15 and E30 insulation and integrity times respectfully things like steel of half mm thickness or 30 8 mm of Timber or mineral wool or 12 mm mm of CES board are readily identified by the document cavity barriers should be fixed and any remaining gaps between the cavity barrier and the surface it up puts should be fire stopped opening in cavity barriers can be done by but are restricted in section six loadbearing elements of structure Flats Now we move to Flats where the approved guidance similarly is similar to dwellings follows the same philosophy of structural integrity and Division and and highlights the possible further consideration of such bearing compartment walls which are expanded on and addressed in several other sections when considering conversion of a dwelling house to Flats any shortfalls of the existing construction should be addressed but maybe within R I3 fire resistance consideration for building of less than three stories if a protected stairway exists or is proposed okay second section seven compartmentation sprinklers in Flats basically unless it is the wall or floor dividing parts of the flat itself it will need to have fire rated construction including between the flat and the refug shoot or places of special fire hazards compartment walls of masonry or Concrete Construction can be bridged by structural elements but to minimum extent and shall be fire stopped when it comes to sprinklers blocks of flats with a top story above 11 11 M measured off of ground level level should be fitted with one the consideration starts with systems inside the flats and spreads to Escape Route if it is not fire sterile separation between buildings should be in continuous vertical plane in form of the wall no flying three hole type of scenarios similarly in division of SE seate parts of buildings in other cases it is enough if the compartment walls are full story high but if they enclose the top story they should form a fire parit over there are further Pro further Provisions for all the elements that are booty or or are supported of the compartment walls or floors to either limit their impact on compartment of restrain their or restrain their failure to the connection with the compartment like a curtain wall type of scenario which should not detach and fly away from the building essentially creating a fire kite spreading the fire and danger danger way over the immediate Environ all perforations will need to be fir stopped and be of certain specification shafts of any use should be protected and compartmental ized as however there are rules for penetrations axes and ventilations and within some certain limits some of the enclosure can be glazed and the external walls often do not need to be fire rated moving to section eight cavities in floods cavities in floods generally fulfill two functions one divice space restraining the spread of Fire Within the cavity and on the other hand all Al closes them to not allow furest spread or ignition from outside sources cavities meaning all hidden spaces most obviously cavity walls but also sus suspended ceilings floors attics cavities should respect the compared mentalization of the building and when the cavities are large this should also be divided into smaller sections section nine protection of openings and fire stopping in the gist all imperfections and perforations through the compartment construction should be fir stopped to inhibit the spread of fire and smoke when it comes to pipe penetration this should have proprietary sleeves or of small internal diameter or sleeved in metal ventilation should not Aid the fire and smoke spread and be fitted with fire and smoke dumpers where needed and in certain circumstan es provide smoke extraction when the Ducks pass through the fire compartment element they should ideally be fire resistant or in fire resistant enclosure and have automatically engaged fire and smoke dumpers look into asfp blue book that's Association for specialist fire protection Blue Book for the best approach to the Mattis interestingly flu or flu enclosure should be of half the fire rating provided by compartment wall otherwise in a way we deal with two walls in any given scenario of the flu enclosure so the total will still equal the required protection the great wealth of knowledge can be assessed through the association for specialist fire protection so you are encouraged to reach out and visit their resources to devour all that good knowledge and this is it for requirement requirement B3 fire spread structures now we're moving on to requirement B before external fire spread so what does the requirement actually say as written in the in the letter of low external fire spread before two points point one the external walls of the building shall adequately resist the spread of fire over the walls and from one building to another having regard to the height use and position of the building point two the roof of the building shall adequately resist the spread of fire over the roof and from one building to another having regard to the use and position of the building in the gist the wall should not be susceptible to ignition and to becoming a torch and the fire should not spread between the buildings walls and roofs as well as through the radiant heat via openings in the walls and roofs all right class dismissed no joking there's still more to go let's see what the guidance have to say in section 10 resisting fire spread over external walls walls should be should meet the performance criteria given in BR report BR 135 or provision on the approved document material should generally have limited combustibility or little a medium contribution to fire all the levels of material reaction to fire will depend on the type and height of the building interestingly cavity walls are excluded from the consideration so can have combustible material within the cavity well at least outside regulation 72 consideration that is the guidance also directs us for more answers regarding performance of green roofs and walls that is contained in other Publications cavities are important to limit the spread of fire obviously there are some extra provision for external balconies in buildings with a story over 11 m in height notably the balcony cannot be turned into a barbecue I know I mean the S should not be perforated and the balcony should not contribute to fire there is a mention on the Restriction of metal sandwich panels which with cause of cause consistence of materials that are more than 35 megga per kilogram of gross colorific value so it means how much of heat it will release upon ignition when the building falls under the remid of Regulation 7 most of the materials used in the external envelope envelope or things attached to it excluding items mentioned in regulation 7 paragraph 3 should be of very limited com combustibility moving to section 11 resisting fire spread from one building to another the risk of spread of fire is all dependent on the use of the building its comp compartmentalization and suppression system present in the building the consideration of the fire spread begins at establishing which boundary is relevant and what impact does the fire in the building may have on the neighboring building depending on the possible future or current distance of the wall to the boundary different Provisions for the amount of unprotected areas of the wall can be specified making most of the wall fire enclosed or completely unprotected when the wall is f away from the boundary the unprotected area consideration starts at class C material and below for any materials of 1 mm thick thickness or more some unprotected areas in the wall may be ignored the distance to the boundary is either within 1 M or over to determine the areas and distances the guidance produces several diagrams and rules to follow but also allows for the use of bra report br1 187 as an alternative approach generally speaking for small buildings the amount of unprotected area in the wall at or closer to the boundary than 1 meter is 5 5.6 M squared that's quite a bit all the smaller openings that generally can be ignored can be added to to that without without decreasing the the amount for the big ones and can be ignored the amount of unprotected wall area grows to unlimited for the walls that are at 6 M away from the relevant BN or if the building is of a of a classification of bigger buildings and more complicated buildings they we take in consideration the percentage of the wall area which starts at 4% at 1 M or less distance from the relevant boundary in buildings with sprinkler systems the boundary distance can be halfed to minimum of 1 M or area of the unprotected wall can be doubled section 12 resisting fire spread over roof covering it is important to say here that roof covering does not include the structure as a whole the covering products accepted by European directive 9106 are fine for use as our roof lights with some limits obviously generally any material can be used on a remote building of at least 20 M distance to the revelent part boundary but the designation of the roof increases to the maximum of the B roof T4 type for the roofs 6 M and closer to that relevant boundary so here you have it approve document B requirement B3 and B4 under the belt [Music] let's recap requirement B free focuses on maintaining a building stability during a fire event emphasizing measures to inhibit fire spread both within the building and between separate structures it mandates subdivision of buildings with fire resistant construction and installation of automatic fire suppression systems were necessary addition it requires the inhibition of unseen fire and smoke spread within concealed spaces section five deals with the internal fire spread in dwelling houses stipulating protection times for structural elements to ensure the stability during fire incidents new additions to existing structures such as additional stories must meet specific fire resistance requirements also compartmentation plan plays a crucial role in preventing fire spread between separate houses and between houses and garages garage design must prevent the transfer of fuel to the house ensuring door slopes away and erased threshold section six addresses loadbearing elements of structuring flats emphasizing the importance of structural integrity and division particularly regarding compart compartment walls section seven underscores the necessity of fire rated Construction in Flats extending to fire shoots and areas of special fire hazards sprinkler systems are mandated for Flats with top stories above a certain height section eight deles into a cavity protection in floods emphasizing the need to divide and close cavities to prevent fire spread section nine focuses on protecting openings and fire stopping to inhibit fire and smoke spread through imperfections in compartment construction and due to perforations it highlights the need for proper pipe penetration and ventilation systems requirement B4 addresses external fire spread emphasizing the needs for external walls and roofs to resist fire spread between buildings it outlines criteria for materials used in wall construction including provision for external balconies section 10 discusses resisting F spread over exteror walls emphasizing material performance criteria and exclusion of cavity walls from certain regulations Section 11 tackles fire spread from one building to another considering building use compartmentalization and suppression systems it provides guidelines for determin determining unprotected areas in walls based on distance to the relevant boundary section 12 focuses on resisting fire spread over roof coverings emphasizing compliance with European directives and specific requirements based on distance to relevant boundaries in summary these regulations aim to ensure structural integrity and inhibit fire spread within and between buildings they provide detailed guidance on fire resistant construction materials compartmentation and protection measures to mitigate the impact of fire incidents compliance with these regulations is essential to enhance overall fire safety in buildings in the next episode I will cover requirement B5 access and facilities for the fire service and see what is hiding in the appendices a2g [Music] now a few words from me I hope you enjoyed this episode and that the considerations of fire safety requirements B3 and B4 I trust it should be making more sense to you now if you have any questions reach out to me on LinkedIn or send me an email I'm more than happy to help you out in BNA we deal with planning designing and managing of of your projects and we are always glad to facilitate a free initial consultation to steer you in the right direction visit www.co.za of non obligatory advice at Bitner we help our clients design and execute their dream homes or Investments if your building is failing falling apart we can also help investigate the reasons behind it and to provide you with an appropriate strategy design and specifications for the repair thank you again for listening please voice up your opinions I'm waiting for you on LinkedIn and I want to hear from you remember Bytnar Designs the Wall Around You Toodloo!
Piotr Bytnar BEng (Hons) MSc CEng MIStructE
Chartered Structural Engineer who deals with the Architecture of buildings. His Master's Studies led him to an in-depth understanding of risk and contract arrangements in construction as well as specialist knowledge in soil mechanics.
He and his team help homeowners and property developers to design and deliver construction projects reducing waste in time and the cost. He believes that the construction project is an iterative process that can be well managed and it is best managed if all the aspects of the project definition and management are dealt with in-house or coordinated by one organisation. His team works to all stages of RIBA and ISTRUCTE stages of work and enables contractors to deliver projects on-site providing risk evaluations, methodologies for execution of works and temporary works designs.
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