EPISODE: 015 - APPROVED DOCUMENT B - FIRE SAFETY - PART 2 OF 4

BYTNAR - TALKS

EPISODE 015 - APPROVED DOCUMENT B - FIRE SAFETY - PART 2 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 means of escape requirements for dwelling houses according to Approved Document B?

• How should escape routes be designed for buildings over 4.5m in height?

• What are the standards for protected stairways in residential buildings for fire safety?

• What accessibility criteria must escape windows and doors meet for effective fire evacuation?

• How is fire containment managed in flats to ensure occupant safety during a fire?

• What regulations exist for emergency access routes in apartment buildings, particularly concerning ventilation and lighting?

• How are evacuation distances regulated in buildings with multiple flats, and what are the provisions for alternative exits?

• What are the requirements for internal fire spread prevention in terms of material linings and flame resistance?

• What restrictions are placed on the use of insulated panels and thermoplastic materials for fire safety purposes?

LET'S TALK ABOUT YOUR PROJECT

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This is Bytnar Talks: The Engineer Takes on Construction, Episode 15.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 cornerstone on which I've built my business, is finding clever solutions for construction projects.

I am a Chartered Structural Engineer and a budding software developer, so you can rest assured that I will strive to talk about 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 — Fire Safety, Part Two [Music]

Hi there, and welcome back to Bytnar Talks, your favorite podcast on all matters of architecture, engineering, and construction. It is Thursday, the 9th of May, 2024, and I'm here back with you with the 15th episode and further information on fire safety.

Fire safety will take several episodes to go through, so buckle up, Dorothy — we’re going down the rabbit hole, and it is a deep one indeed.

Last week in Episode 14, I started talking about the Approved Document B — Fire Safety — and introduced you to Volume 1 and its initial sections: Section 0 and 1. I mentioned that the approach to fire safety will generally follow the risk profile of the particular building, assigning different purpose group levels to different buildings.

In this episode, I'll carry on talking about Volume 1, Purpose Group 1A to 1C — so: flats, houses with floor levels between 4.5 to 18 meters in height, and houses with floors at levels under 4.5 meters in height.

An alternative approach to Approved Document guidance is available, and you can use a fire safety engineering approach using, for example, British Standard 7974 and ancillary published documents. But the approach cannot be less safe than that of the Approved Documents.

Now I'll finish talking about Requirement B1 of the Building Regulations, with concerns addressed in Sections 2 and 3 — means of escape from dwelling houses and flats — and move to Requirement B2 — internal fire spread: linings, addressed in Section 4 of the Approved Documents.

So, without further ado, let's dive into the fire safety requirements B1 and B2 as treated in the Approved Documents.

Now I'm going to talk about Sections 2, 3, and 4 of the Approved Document B, Volume 1 — sections that deal with the means of escape from dwelling houses and flats, as well as the internal fire spread due to linings of walls and ceilings.

In this episode, you will find out what to take into consideration and why. And I will stop to ponder a little bit on the situation when a building changes the group from 1B to 1C due to the vertical extension of the house — either by the creation of a full storey over the existing building or changing the loft space into habitable space, either by simple attic conversion or otherwise.

Let us start with means of escape from dwelling houses.

In the document, you'll note a diagram showing different possibilities, which generally cover the following circumstances:

1. Escape from the ground floor.

2. Escape from upper storeys at a maximum of 4.5 meters above ground level.

3. Escape from storeys over the 4.5-meter limit, which further divides consideration into the situation where there is only one storey over that limit, and where there are two or more storeys over that limit.

The guidance recognizes increasing risk with the height of the building and the reduction of possible escape alternatives for its occupants. It is easy to imagine that you can jump out of a window at the ground floor or even first floor of your building — but going higher, the drop will make it increasingly more difficult to evacuate.

An important matter to consider is the inclusivity of the building. You cannot expect all people — or people with inhibited mobility — to jump out of windows. They can certainly be lowered down through the window at the ground or first floor, but dropping such a person from too high would amount to manslaughter.

The guidance for the ground storey is either to allow habitable rooms to have direct exits through a window or door, or through a hall. For storeys under 4.5 meters in height (measured from ground level), we can allow people to escape through a direct exit — window or door — but if not possible, there should be a protected stair in place.

Interestingly, if you want to connect rooms internally — like in the case of a Jack and Jill bathroom — only one room needs to have the direct exit if there is no provision of a protected stairway or stairwell. Both ground floors and first floors can have inner rooms if the room has a direct evacuation option, like an escape window.

Now, knowing the rules allowed for floors at higher levels — though — and what is an inner room, you ask?

It is the room that has no other way to exit but to go through the doors leading to another room, otherwise called an access room. It could be a basement room, man cave, bedrooms sharing living space — generally, any room — but not a room solely used for circulation, like a vestibule or porch.

Some inner rooms are allowed, like kitchens, laundries or utility rooms, dressing rooms, bathrooms, water closets or showers, or galleries — within reason. And access rooms will need to have smoke alarms and cannot be kitchens. You cannot walk through the kitchen to try to escape from another room, as the kitchen is one of the most likely places where a fire can start.

Now, when we move through the threshold of 4.5 meters at the next storey level, we need to think protected stairwell, or several stairways. If we have several stairways, they need to be separated so that the eventual incapacitation of one way of exit does not affect the other — meaning either fire-resistant construction between them, or a room between them, giving you two different walls, which would, at the end of the day, satisfy the requirement of fire separation.

If there is only one escape stairway, it needs to be protected to REI 30 construction — or RE 30 construction.

What does that mean?

It means that the enclosure will need to hold for 30 minutes in respect to:

• R – Structural consideration (load-bearing capacity of the enclosure),

• E – Integrity (it remains in place to hold flame and smoke out),

• I – Insulation (limits the temperature on the other side of the wall to 140° Centigrade).

Sometimes, you may choose to reduce the radiant heat only, and that falls under the letter W — radiant heat transmission limited to 15 kW per square metre — usable when you want to divide space with glass.

The protected stairway should go straight to the Final Exit, or it could split into two alternative exits, going through other rooms. These rooms need to be separated with fire construction and cannot be inner rooms.

If there is only one storey over the 4.5-meter consideration, we can cut it away from the rule by using REI construction between that storey and the one below, and provide an alternative escape route.

In any case, the protected stairwell needs to ensure that its ceiling, or soffit, is protected to stop any fire spread through it.

For dwelling houses with two or more storeys over the 4.5-meter limit, storeys at levels over 7.5 meters should have an alternative escape route, isolated from the bottom storeys, or a sprinkler system throughout.

For passenger lifts over 4.5 meters above the ground level, the lift shaft should either be:

• within the protected stairwell enclosure, or

• enclosed by fire-resistant construction itself.

So, how about the ventilation?

It’s simple in buildings with floor levels under the 4.5-meter limit — no special considerations are needed. But when that limit is exceeded, the staircase should be isolated from the rest of the house, and any penetrations should be fire-stopped.

Ducts in rigid steel, mechanical ventilation recirculating air into the stairwell must stop upon smoke detection. And warm-air heating systems should be limited to 27°C, measured in the living room at mid-room height.

Now let’s get some definitions, shall we?

What is an escape window or door?Well, it needs to be wide or high enough to allow a man with a belly through — meaning:

• 450 mm in width (minimum),

• 1.1 m in height (maximum sill level), and

• a minimum of 0.33 m² in area.

Going with the minimum width, the opening should be at least 734 mm in the other dimension.

This can prove difficult for obese people and people with mobility problems. I generally recommend a fully openable window whenever possible. Windows can have locks and childproofing, but they need to remain open once opened.

The escapee should be able to reach a safe distance from the house — of at least the building’s height away from the building, or the height of any immediate extension, whichever is greater.

So what is the “within reason” requirement for galleries in rooms?First of all, there is no limit on the area of the gallery — if provided with an alternative exit or escape window. If under 4.5 m level, consideration in relation to the ground level, or it cannot be bigger than 50% of the room, including stairs — stairs within 7.5 m at gallery level and 3 m away from the exit from the room.

If you want to evacuate through the flat roof or the balcony, it needs to be safe to do so — meaning REI construction, and it must be guarded from trips and falls, and lead to a storey exit or external escape route.

Habitable rooms in basements should have an escape window, external door, or access to a protected stairway. External escape routes are possible, with limits imposed by the guidance and extra weatherproofing. If the stairs lead to storeys over 6 m in height, fire-resisting construction should extend:

• 1.1 m vertically up over the top landing (excluding basements to ground floor escape),

• 1.2 m horizontally on either side, and

• 9 m vertically down.

Just imagine a raging fire — how far away from that fire do you think you'll need to be to be able to pass by safely?1.1, 1.2, and 9 m are generally good indicators. Well, I'm not sure about the 1.1 m, but sure — you can crawl when you're at the top!

There are some additional or “otherwise” considerations for works on existing dwellings — notably when the work is to the windows. If replaced, they need to be not worse than previously or not less than the minimum required, and may require the installation of cavity barriers.

When you do a loft conversion, you need to make sure there is a protected stair introduced with:

• REI 30 construction,

• E20 fire doors.

And when the work is on historic doors, measures may be taken to attempt an increase of fire protection to E20.

If the protected stairwell is open at the ground floor, you need to provide sprinkler protection to the open plan. You must also separate the ground floor from the first floor to allow loft occupants to exit through the first floor window, when the sprinkler system does not work, and provide an enclosed kitchen with REI-rated construction.

So basically, it means if you have an open-plan kitchen that connects to your stairwell, you’ll have to close that space — well, at least close the kitchen or provide a sprinkler system if you still want your living space to be open to the stairwell. But then again, you'll need to do a bit of closing up on the first storey to enable all of the loft occupants to go through the first-floor room window.

So — quite, quite involved.And it’s rather more cost-effective to basically provide one unobscured and direct exit from that loft, within the protected stairwell with REI 30 and E20 doors.

[Music]

Off to Section 3: Means of Escape – Flats

Generally, the philosophy of the approach is similar to that for dwelling houses, but the communal circulation areas are treated separately from the space within the flat.

And yes — you can jump out the window if you can — if the floor level is under 4.5 m in height.

The approach follows the following considerations:

• That the fire is contained to the flat,

• But localized fires can happen,

• No external rescue is considered,

• There’s unlikely simultaneous evacuation required.

Stay put strategy is considered here — confining the fire to the flat and allowing relatively little of the heat and smoke through the exit.

In mixed-use buildings, separate escape routes should be provided — except in special circumstances, when habitable space is ancillary to the use of the main building and very small.

The flat arrangement follows that of the dwelling, but with the final exit being the flat entrance.

In flats where no reliance can be made on escape windows, the escape from any room — when the hall is of REI 30 — should not be further than 9 m, or, if there is no protected hallway, 9 m from the furthest point of any room. And there cannot be a kitchen in the way — or at least not within 1.8 m of any escape route.

You see — imagine a raging oil fire on the hob. That 1.8 m distance, if that ever happened to you, seems to be a good guideline for deciding if the kitchen is or is not in the way.

Separation of living and sleeping sections of the house is also possible, with the addition of an alternative exit, when otherwise an inner room scenario occurs within the flat.

When evacuating the flat, a person should be able to change direction of evacuation if encountering a raging fire from some other flat in their way. This provision is generally achieved by excluding sway, either by lobby or corridor separation.

Escape distance from any flat should not exceed:

• 7.5 m for one-way consideration, and

• 30 m for two-way consideration — meaning access to a protected stairwell, either one or more.

The travel distance may be reduced to 4.5 m.Protected access to the stairwell and corridor should be ventilated to remove smoke.

General protection for the protected stairwell goes to REI 60, and all other protected spaces to REI 30, with self-closing doors of E30 category. Head height should be a minimum of 2 m, but this does not include door frames, which may be lower.

Emergency lighting should be provided and emergency routes clearly marked.

Refuge chutes should be isolated from the escape routes and flats.

External staircases can be used, but they are limited:

• to 6 m over ground for the only escape staircase, and

• 6 m over podiums or roofs if the building and that roof is also served by an internal staircase.

Power circuits should be sufficiently protected, and circuits required for firefighting should run through areas of low fire probability.

There are further requirements for the stairs, doors, final exits, and lifts, and they all follow logically and are logically tied to:

• allow people uninterrupted exit when needed, and

• to provide enough fire resistance in the event of fire.

This concludes Requirement B1: Means of Escape – Dwellings and Flats.

Now I'll tell you a little bit about Requirement B2: Internal Fire Spread – Linings.

So, what does the legislation say?

Requirement B2 has two points: 1 and 2.

1 says to inhibit the spread of fire within the building, the internal linings shall:a) adequately resist the spread of flame over their surfaces, andb) if ignited, have either a rate of heat release or a rate of fire growth which is reasonable in the circumstances.

2 says that in this paragraph, "internal lining" means the materials or products used in linings of any partition, wall, ceiling, or other internal structure.

This essentially means: no carpets on the ceilings and walls — well, maybe — but the intention is to minimize the spread of fire through the fabric of the building internally.

The smoke and fume generation, floor and stair coverings, and furnishings are not considered under this section.

In general, all lining materials can:

• produce high-intensity dripping droplets, classified as D2,

• produce high emissions of smoke with high volume and intensity, and

• be combustible.

However, depending on location, linings can be of fire class B to D — meaning:

• B: very limited contribution to fire,

• C: limited contribution,

• D: medium contribution.

So:

• Circulation spaces,

• Rooms in general,

• Garages and small rooms,

and garage sections of walls can be of poorer quality, within certain limits.

Framing of doors and windows generally does not fall within the consideration.

Special consideration should be given when:

• Insulated panels are used, or

• PTFE membranes (or similar) are involved.

The use of thermoplastics is conditioned — plastic that deforms or is consumed with a rise in temperature.

For windows, roof lights, and lighting diffusers, the following are generally fine:

• Class TP(a) Rigid, which extinguishes when the source of fuel is removed (and is thick enough to do that), or

• TP(b) with limited fire-rated applications placed away from circulation areas and within specified limits.

So perhaps, at the end of the day, a carpet could be hung on the wall — after all.

So here you have it: Approved Document B, Sections 2, 3, and 4 — under the belt.

Section 2 of the document outlines means of escape for dwelling houses, emphasizing different scenarios based on building height and layout. Ground floors can utilize direct exits, while upper storeys within 4.5 m of ground level may use direct exits or protected stairwells. Buildings over 4.5 m require protected stairways meeting REI standards. Escape windows and doors must meet specific accessibility criteria.

Section 3, which covers means of escape from flats, focuses on containment within units and controlled evacuation. Separation of living and sleeping areas enhances safety, and emergency access routes must be well-ventilated and illuminated. Evacuation distances are regulated, with provisions for alternative exits.

Section 4, Requirement B2, addresses internal fire spread within buildings. Materials used for linings must resist flame spread and have reasonable heat release rates. Special considerations are given to insulated panels and thermoplastic materials, with restrictions based on fire resistance and application location.

In the next episode, I will cover Requirement B3 and B4 — so:Internal fire spread (structure) and external fire spread, Sections 5 to 12.

I hope you enjoyed this episode and that the consideration of fire safety escape in dwellings, as well as internal fire spread, begins to make more sense to 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 me 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 repair.

Thank you again for listening!Please voice your opinions — I'm waiting for you on LinkedIn and I want to hear from you.

Toodloo! 👋

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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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