EPISODE: 018 - APPROVED DOCUMENT B - FIRE SAFETY - VOLUME II - PART 1 OF 2
- Piotr Bytnar BEng (Hons) MSc CEng MIStructE
- Nov 5, 2024
- 18 min read
Updated: Jun 19
BYTNAR - TALKS
EPISODE 018 - APPROVED DOCUMENT B - FIRE SAFETY - VOLUME II - PART 1 OF 2
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 fire safety requirements for non-dwelling buildings under Approved Document B Volume II?
How are fire detection and alarm systems classified for non-residential buildings?
What is the purpose of horizontal escape routes in fire safety planning for office buildings?
What considerations are there for vertical escape design in high-rise office buildings?
What are the simpler fire safety provisions for small premises under 280m²?
How should internal linings be classified to resist flame spread in commercial buildings?
What alternative approaches are allowed for fire safety compliance in non-dwelling buildings?
How should mixed-use buildings handle fire safety regulations across different purpose groups?
What are the special fire safety requirements for healthcare and institutional buildings?
This is Bytnar Talks – The Engineer Takes on Construction, Episode 18
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.
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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: Fire Safety – Volume Two, Part One
Hi there, and welcome to Bytnar Talks — your favourite podcast on all matters of architecture, engineering, and construction.
It is Thursday, the 30th of May 2024, and I’m back with you with the 18th episode and further information on fire safety in building.
Today, we’re moving along to Volume Two of Approved Document B and talking about the discharge of Building Regulations concerning buildings other than dwellings.
Last week, in Episode 17, I talked about Requirement B5 – Access and Facilities from Volume One of the Approved Document:
What type of information is required under Regulation 38,
What is hidden in the Appendices (which are shared between both volumes).
That episode covered the considerations and provisions required for:
Vehicle and appliance access,
Ensuring the firefighting crew is able to sufficiently fight the fire,
Distances of water outlets and backup inlets — whether in the form of a hydrant, or dry/wet fire mains,
Protected shafts, and
Provisions for heat and smoke ventilation in basements,
As well as the required information about the system layouts, construction, capacity, and strategies for when the fire breaks out.
In this episode, I will cover:
Requirement B1 – Means of Warning and Escape, and
Requirement B2 – Internal Fire Spread (Linings),from Volume Two, and the introduction to the document, covering Sections 0 to 6.
Now, this material is about buildings other than dwellings, which are covered in Volume Two of the Approved Document B. It consists of 20 sections providing guidance on all the requirements of the Building Regulations, plus appendices, which are mutual for both:
Volume One (Dwellings), and
Volume Two (Buildings other than dwellings).
So I won’t be coming back to the appendices in this material — they’ve already been covered in previous episodes.
Today, I will cover:
Sections 0 to 6, which include:
Requirement B1: Means of Warning and Escape, and
Requirement B2: Internal Fire Spread – Linings.
We'll start with Section 0, which outlines:
General information, and
The approach that should be taken when using the guidance of this document.
Then, Sections 1 to 5 cover:
Fire detection and alarm systems,
Horizontal and vertical escape routes,
Guidance for small premises, and
Other general provisions.
Section 6 will cover:
Wall and ceiling linings.
It is important to understand:
Why and how we should use this guidance,
What level of consideration is required when approaching the specification and design of buildings other than dwellings,
What classes of buildings are considered, and
How the specification varies between them.
So — let’s dive straight into it, shall we?
This material is about buildings other than dwellings, covered in Volume Two of Approved Document B. It offers guidance for discharging:
Requirements B1 to B5, and
Regulation 38 of the Building Regulations.
The document also describes the assumptions made when forming the guidance.
Section 0 mentions key elements like:
The management of the premises, which — while not covered directly by the regulation — is assumed to be in place and maintained by the building owner.
Failure to manage this properly may result in prosecution under other legislation.
It’s important to understand that:
This guidance focuses on life safety,
Not on the protection of the premises itself.
So a more stringent approach may be needed for property protection — and the Fire Protection Association would be the right place to turn for that additional information.
The guidance aims to be inclusive — to cater for most people in most situations. Therefore, exclusion of building user should not form part of the considerations except in special cases. And there also may be such special cases that the guidance does not cover, but the design approach should cater for. So — don’t follow it blindly. Look at it holistically. Don’t exclude people that use the building, and you should be good to go.
As with the previous volume, alternative approaches to the guidance can be made, but will need to be of minimum equivalent safety to that contained within the guidance of the Approved Document. It should form a coherent, holistic whole.
Some special consideration will be needed for buildings containing more hazardous operations — like battery production, fireworks, power plants, and whatnot.
Special consideration should also follow for healthcare premises, and the information contained within the Department of Health publication called Firecode.
Unsupervised group homes should either follow:
The Department of Health Health Technical Memorandum 88 (HTM 88), which deals with fire precautions in housing providing NHS-supported living in the community for small buildings,
Or otherwise, be treated as Purpose Group 2B.
Shopping complexes or buildings with atria passing through compartment floors are better treated with the approach of British Standard 9999, as are assembly buildings — though some special consideration needs to be taken in line with the Safety of Sports Grounds Act 1975.
Schools, on the other hand, are covered in Building Bulletin 100.
Special considerations are also due to prisons, which are exempt from the Building Regulations. However, their approach is regulated by separate legislation, and the correct method is found in the HMPPS Custodial Premises Fire Safety Design Guide.
Some leeway can be found when approaching historic buildings, but as ever — if there is an issue or ambiguity, the only solution for the specification may be the approach of fire safety engineering, as covered in British Standard 7974 and ancillary supporting published documents.
I’ve mentioned Purpose Groups when assigning the risk level to the Assisted Living premises — and that is what Purpose Groups are for. They group typical buildings into risk classifications, and there are seven groups total, though only six are covered in Volume Two of the Approved Documents.
These are:
Group 2: Residential (where people sleep overnight)
Type A – Institutional
Type B – Other
Group 3: Offices
Group 4: Shops and Commercial spaces
Group 5: Assembly and Recreation
Group 6: Industrial
Group 7: Storage and Other Non-residential
This last group further divides into:
Group 7A – Any buildings not in Groups 1 to 6, and not 7B
Group 7B – Special provisions for car parks for small vehicles (up to 2.5 tonnes gross weight)
As however, if there is mixed use in play, the consideration should be divided if the auxiliary space is large enough, or is between flats and other groups. If in doubt, use the more stringent approach.
In complicated circumstances, the requirements may well fall outside the general guidance, and the fire safety engineering principles may be necessary to assure the fire safety.
So, off to our first requirement — Requirement B1: Means of Warning and Escape.
As ever, let’s start with finding out what the legislation requires of us — in its own words.
Means of Warning and Escape – B1:
“The building shall be designed and constructed so that there are appropriate provisions for the early warning of fire, and appropriate means of escape in case of fire, from the building to a place of safety outside the building — capable of being safely and effectively used at all material times.”
It seems relatively simple, right?
And the Secretary of State is also of simple intention here — just as long as there is enough warning, and a safe and well-signed escape route that people of different capabilities can use, the requirement is pretty much covered.
Naturally, this will mean many different things to many different buildings and complexities — but that is why there are Purpose Groups in place, to make it a little simpler.
Section 1 deals with Fire Detection and Alarm Systems.
In the gist:The alarm needs to be sufficient.
So if you work in a car garage, it may be enough to shout that there’s a fire in the corner — or there's a fire in a car — and everyone will know.
But as buildings get more complex, more onerous provisions will need to be put in place. Fire detection systems should be automatic and form controlled networks of sensors — either heat, smoke, gas, or radiation — or be activated through a sprinkler system. This will be mandatory in residential-type scenarios but will follow different considerations in other purpose groups.
Generally speaking, if there is a room where people rarely go, where a fire can start and it would inhibit escape from the building, then an appropriate system should be in place to alarm people of such an event. Or, where the building is otherwise secured for entry or has a pressure differential system counteracting the ingress of smoke into the escape way — such provision should also be made.
The selection of the system should follow British Standard 5839, which categorizes different systems into three different categories: L, M, and P.
Category L is for the protection of life, which is further broken down into five levels of consideration:
L1 is a total coverage system.
L2 is defined part system.
L3 is for early warning to allow escape.
L4 is an escape route system.
L5 is a system for a specific fire objective.
Category M deals with manual fire detection and alarm systems.
Category P is about property protection, further divided into:
P1 – Installed throughout the building.
P2 – Installed only in specific parts of the building.
With the chosen category in mind, it needs to be established what goes where, and how the alarm should be sounded — which will differ between staged and simultaneous evacuation plans, especially in buildings with a large number of people or where the occupants are not familiar with how to behave in the event of fire.
Provision for visual alarms for hearing-impaired people or personal vibrating paging systems may also be appropriate in certain circumstances.
In any case, the design, installation, and maintenance of the system, as well as its interface with other systems, should be controlled to ensure its reliability.
For certain limits of student flats accommodation, there should also be a separate automatic detection system in each individual flat.
Leaving alarm considerations behind, Section 2 – Design for Horizontal Escape deals with the immediate escape route to the exit or protected stairway.
The principle of this approach is: if anyone is confronted by fire, they should be able to turn away from the fire and escape safely.
If the building is not larger than two storeys plus a basement, and no storey is larger than 280 m², the building will be considered small, and a slightly relaxed approach can be taken.
When considering escape routes, we need to consider:
The number of people needing to vacate the space,
Their travel distance to the nearest exit, and
How many vertical escape routes there are — so that access is possible from any point in the space.
There also needs to be separate escape routes for:
Dwellings and flats,
Assembly and recreation spaces — when mixed-use buildings are in play.
Number of Escape Routes:
Single escape routes are allowed with limitations on the distance and the number of people who must use them.Typically:
30 people max in rooms used for residential and institutional purposes,
60 people max in bars, assembly spaces, and
60 people max for a single-storey occupancy.
Distance limits begin at:
9 m from a dead end in residential, disabled persons' buildings, and places with special fire hazards,
Up to 60 m in open air.
Consequently, the distances can be extended for escape in more than one direction, starting at 80 m and up to 100 m in open-air environments.
There are rules on how to measure these distances, and limits to the relative position between the routes — like a minimum 45° angle between the points of turn and the routes to alternate exits.
Minimum Number of Escape Routes:
One is enough for up to 60 people,
Two are required between 60 and 600 people,
Three are needed for more than 600 people in most cases.
In reality, the number of escape routes will be governed by the travel distance more than the headcount.
Inner rooms are allowed but should either:
Have alternative exits, or
Comply with the distance and visibility limits imposed by the guidance.
In essence, people should be able to see if a fire starts in the access room and be able to leave safely.
So:
A room cannot host too many people:
30 people max for residential,
60 people max in other cases.
Exits into central courts should be separated by corridors or lobbies.
Escape routes should also: be away from openings in the same storey, and not go through a zone within a 4.5 m offset around the opening access to alternative story exits can be through protected lobbies, but not through the other protected stairway. It is also important to separate circulation routes from protected stairways by at least means of self-closing fire doors with automated release mechanisms—meaning if there is some sort of circuit failure or in the event of fire, the doors will be released to enclose the protected stairway.
Stories of mixed use or occupancy may require consideration of separation and alternative exits—like in the case of restaurants or bars—or be divided by at least a protected corridor with provisions for automatic fire detection and alarm.
Width of escape route starts at 750 mm—or, well, 530 mm if you count the space between fixed storage racking—to slightly over 1 m for up to 220 people using the route. Over this limit of 220 people traversing the exit, we need to allow for 5 mm per person.
For alternative routes, we should discount one, as it may be blocked. So the story may need to use the alternative only, and that alternative needs to be capable of allowing enough people through. Similarly, for the final exit, which will need to accommodate the story load of people plus the stairway.
So, how to establish the lobby exit? Well, in the worst-case scenario, it should be of the story exit width summed up with the stair’s width—but it can be smaller in certain conditions and needs to follow the formula, which is basically 75% of the stair width plus 0.5% of the number of people served by that story exit.
Corridors need to be protected when serving bedrooms or mixed occupancy, and dead ends of more than 2 m depth. In other cases where they do not need to be fire-rated, they need to provide enough division to stop smoke penetration at or over the ceiling level.
For dead-end corridors of over 4.5 meters, we are guided to provide protected access to the point of alternative exit. Escape through the external routes or flat roofs is possible with certain limits—like if protected within 1.8 m of route horizontally and 1.1 m vertically and of fire-rated construction in the case of the roof. Also, the roof route needs to be one of the alternative routes and cannot be specified in residential, institutional buildings and buildings where there is public use.
Special considerations are needed for buildings where people will need to be assisted to live—like in cases of residential care homes, where a progressive horizontal evacuation (PHE) strategy may be needed. If the fire code document applies, its recommendations should be used instead.
The PHE strategy requires more frequent compartmentalization to allow incremental movement of people from the area with fire to the next compartment. Bedrooms should form compartments, as well as auxiliary rooms where the fire can start. The care home should be fitted with the highest level of alarm—class L1—in line with BS 5839.
Installation of a sprinkler system allows for more design freedom in these types of circumstances.
Now to section three: Design for vertical escape. In the building, there needs to be enough stairs and of easy use to allow the escape, even for people with restrained mobility. So if the building is fine for use with a single stairway for each story, such a building can be served by a single stairway within the additional limits for vertical escape routes.
Generally, small and not complicated buildings with story level under 11 meters over the ground level, or small offices up to five stories, with stories over 11 meters having separate provisions for escape. Refuge should be provided at each usable story—protected area or via stairway—and must meet certain criteria, including marking and provision of emergency voice communication systems.
The width of the escape stairs is regulated but will follow the consideration of the number of people to be evacuated, the modes of evacuation (whether simultaneous or staged), wave of access doors, purpose group, and so on.
Where there is more than one staircase for each evacuation scenario, one staircase should be incapacitated in any given scenario. The calculation of capacities is shown in the approved document.
Additionally, rules on the material use—typically A2-s3, d2—ladder use, single step, helical or spiral stairs, is also mentioned.
Generally, the provision of fire-resistant construction of the enclosure should be observed. External staircases can be used if there are also internal alternatives. External staircases need to be positioned within fire protected zone of 1 m down, 1.8 m either side, and 1.1 m to the top, and protected from elements if higher than 6 m. Use of protected lobbies and corridors accessing protected stairways is generally considered a good idea, but it does not need to be the case in line with the guidance. If the protected stairways are joined, their enclosures should not be perforated. There are some provisions for having access to toilets or a reception desk, as well as gas installation within those stairways—but all these with further considerations.
Interestingly, for single protected stairways serving upper floors, these need to terminate at the ground level, and separate provisions should be made for the escape from basements. Some different approaches could be observed in Section Four, dealing with small premises.
The small premise is such of single occupancy of no more than three stories, including a single basement story and a first story, and of a size that, if not divided, would allow clear view of all the parts of the story. So, taking the limit of 280 m² max, the area of the story should be generally undivided—except for ancillary spaces and storerooms, which should be fire-rated.
As with any other case, maximum travel distances, number of staircases, and the enclosure are regulated by the guidance.
Section Five deals with general provisions for protected escape routes—whether horizontal or vertical—and service installations. The performance for fire resistance and details of the enclosure is available in Appendix B and C. Glazing that forms part of these enclosures is also treated within the appendices. If the glazing unit can provide enough integrity and insulation, there is no restriction on its use.
Doors should be easy to use and operate in terms of locking, opening, and closing mechanisms, and be of appropriate fire rating. Doors should generally open in the direction of exit, and revolving and automatic doors are allowed; however, alternative escape or opening needs to be put in place.
Escape routes should be at least 2 m high, but could be a bit less at the door frame. In any case, it should allow easy exit by most people over a surface that does not promote slips, trips, and falls.
Final exit should be of the right capacity, well-lit and signed, and inclusive for disabled people. Requirements for different purpose groups are contained within the guidance.
Some further consideration of placement and protection of protected power circuits should be given so as to mitigate failure of the system. When it comes to lifts, it is generally advised not to use them in the event of fire, but certain provisions may need to be made, and the lift adapted for evacuation, or provisions made for the use of firefighting lifts.
For the evacuation lift, the enclosure and shaft should follow the enclosure requirements, dependent on the type and position of the lift, as well as the possibility of the spread of smoke through the lift to protect the shaft. It is advised to have the operating room either at the top of the shaft or separated if top installation cannot be achieved.
Refuse chutes and storage are to be constructed to British Standard 5906. They should be separated from the other parts of buildings with either REI 30 for small buildings (with top story under 5 m above ground level) or REI 60 construction, and be accessed directly from the open air or through a ventilated lobby.
Walk-in and fully enclosed shop rooms should be separated from the retail area with fire-resistant construction—minimum REI 30—if the fire within would impact the means of escape, unless they are fitted with automated fire detection and alarm systems or are fitted with sprinklers.
So, this is it with Requirement B1.
Now let’s have a look at what the legislator prepared for us in Requirement B2: Internal Fire Spread – Linings.
So, B2: there are two points in the legislation. Point one further divides into (a) and (b):
1. To inhibit the spread of fire within the building, the internal lining shall:(a) adequately resist the spread of flame over the surface; and(b) have, if ignited, either a rate of heat release or a rate of fire growth which is reasonable in the circumstances.
2. In this paragraph, internal linings means the materials or products used in lining any partition, wall, ceiling, or other internal structure.
This one is all about assuring that what is put on the walls and ceilings does not fuel the fire, and the spread of fire is somehow restricted.
So, Section 6 tells us what wall and ceiling linings are. Acceptable—the worst classification being D-s3, d2, and best B-s3, d2—so between medium to very limited contribution to fire. But smoke and droplets could be as heavy as they get. Some relaxation on parts of the wall can be introduced, but with limited area and being the worst-case scenario of the D-s3, d2.
Similarly, with ceilings, mention is made of special provisions that are required for ceilings in protected stairways. Consideration is also given to thermoplastics used in windows and rooflights, the use of light diffusers, and the use of suspended or stretched-skin ceilings, recognizing different limits depending on different types of thermoplastics.
Additionally, flexible membrane coverings or PTFE-based materials are to be treated using the approach shown in British Standard 7157 or BRE Report BR 274. The use of insulated core panels also gets attention, as do the fixings and possible delamination of the panel when heated.
So, this is it, folks—first part of the Approved Document B, Volume 2, is under the belt.Volume 2 of the Approved Document B provides guidance on fire safety for non-dwelling buildings, focusing on Requirements B1 to B5 and Regulation 38 of the Building Regulations. The primary concern is life safety—not property protection. The guidance assumes building owners will maintain proper management practices, though these are not directly regulated.
Key considerations of the requirements are inclusivity, alternative approaches, and special consideration for special buildings. Buildings are classified into six purpose groups for risk assessment—Group 2 to Group 7—covering residential, institutional, and other: office, shop and commercial, assembly and recreation, industrial, storage, and other non-residential including car parks for small vehicles. Mixed-use buildings should apply more stringent measures where necessary.
Complex situations may require fire safety engineering to BS 7974 and auxiliary published documents.
Requirement B1—Means of Warning and Escape—tells us that buildings must have adequate early fire warning systems and safe escape routes. Fire detection systems should be automated and follow BS 5839 standard. Categorization follows: Life Protection – Class L, Manual Detection – Class M, and Property Protection – Class P.
In Section One: Fire Detection and alarm Systems, we find that systems must be appropriate for the building's complexity, and designed, installed, and maintained accordingly.
In Section Two: Designed for Horizontal Escape, we find that escape routes must consider occupant numbers, travel distances, and protections like fire doors and corridors. There may be special rules applicable to single and alternative escape routes, inner rooms, and protected stairways.
Section Three: Design of Vertical Escape tells us that we should take special provisions for providing sufficient escape stairs and that we should identify redundancies of the escape route system in any event of fire.
In Section Four: Small Premises, we find some special rules for smaller buildings of up to three stories—with one above and one underground—and a 280 m² maximum story floor area.
And we find out the general provisions for protected escape routes that include fire-resistant enclosures, easy-to-use doors, final exit provisions, protected power circuits, lifts, and refuse chutes—and how to treat them in the backdrop of the regulatiot, The requirement of the regulation.
Requirement B2—Internal Fire Spread: Linings—tells us that the linings must resist flame spread and maintain reasonable heat release and fire growth rates. Classifications range from D-s3, d2 (which are medium contribution) to B-s3, d2 (with limited contribution). Special considerations are given to thermoplastic materials, insulated core panels, and their fixings.
This document ensures non-dwelling buildings adhere to essential fire safety standards. It emphasizes early warning, safe escape routes, and proper internal linings to inhibit fire spread.
In the next episode, we move on to Requirements B3 to B5 and Regulation 38, covering Sections 7 to 19.
I hope you enjoyed this episode and that the considerations of fire safety in Volume 2—Requirements B1 and B2—are now clearer and more comprehensible for you. 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.
At Bytnar, we deal with planning, designing, and managing your projects, and we are always glad to facilitate a free initial consultation to steer you in the right direction. Visit www.bytnar.co.uk and reach out to us—whether your question is "Can you help with my project?" or "What should I do?", we will be able to give you a piece of non-obligatory advice.
At Bytnar, we help our clients design and execute their dream homes or investments. If your building is falling apart, we can also help investigate the reasons behind it and provide you with an appropriate strategy, design, and specifications for the repair.
Thank you again for listening. Please voice your opinions—I'm waiting for you on LinkedIn and I want to hear from you.See you next week—and remember: Bytnar Designs the World 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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