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Britain and Ireland’s unique perspective on the fire safety design of internal flat arrangements 

By: Luke Lister, Charlie Hopkin & Jun Heng Low, Ashton Fire, Manchester, UK

Introduction

This article summarises a short review of the differences in current international fire safety guidance on the internal planning of residential flats. In this article, ‘flat’ refers to an apartment which is a separate and self-contained residential premises forming part of a building, having all its rooms on one level [1]. The UK appears to have a unique position on this matter with restrictions placed on open plan living, the provision of protected entrance halls, internal travel distance limits, and ongoing discussions and changes to guidance over the acceptable location of cooking facilities.

In a review of flat design in England, Hopkin et al. [2] indicate that the origins of fire safety design approaches largely stem back to the British Standard Institution publication ‘Code of Practice CP 3 Chapter IV – precautions against fire’ (CP 3) [3]. In this standard, it was recommended that any flat with a single exit should be designed with an internal protected escape route, e.g., an entrance hall, with ‘no appreciable fire risk’ located in this area. CP 3 suggests the need for these protected escape routes is that should fires occur in kitchens or living rooms (particularly when unoccupied), these present a ‘major threat’ to occupant safety while they are asleep in the bedrooms.

The recommendations stated in CP 3 regarding protected escape routes in flats were subsequently adopted into Approved Document B (ADB) in 1992 [4], and these recommendations have been broadly maintained in the latest revision of ADB vol. 1 (2019 edition with amendments) [5]. These limitations led to further work carried out by the Building Research Establishment (BRE) [6] and others [7], which resulted in alternative recommendations being introduced in the residential fire safety design guidance of British Standards BS 9991:2011 [8], BS 9991:2015 [9] and its draft revision [10]. For brevity, the historical development of these guidance documents has not been reproduced in detail in this article, but further information can be found in the work of Hopkin et al. [2] and Spearpoint et al. [1].

Review Methodology

For the review of international fire safety guidance on internal flat design, standards have primarily been selected if they are written in English (or have an English translation available), if they are readily accessible online, and / or if they are familiar and known to the authors. As such, the review is not intended to be exhaustive and there are many international standards which would not have been captured. The 16 different standards reviewed in this article are displayed later in Table 1, but the review covers the UK, Ireland, New Zealand, Canada, USA, Australia, Finland, Sweden, Denmark, Malaysia, Singapore, and Hong Kong, where the term ‘standard’ is used hereafter to refer to a range of mandatory and non-mandatory technical publications adopted in these jurisdictions.

The review only considers single storey flats entered on the same level, with limited consideration of the impact of the building height or overall building floor area. This approach is taken for comparative purposes of the internal flat design only, as certain guidance documents recommend different fire safety provisions and limitations with increasing building height or overall floor area.

From an initial review of standards, there are three common categories of restrictions placed on internal flat design, which form the basis of the comparison. The following recurring restrictions within the standards are: compartment size limits; limitations on internal travel distances within the flat; and the location of the kitchen / cooking facilities.

Design Guidance from Britain and Ireland

This section provides a summary of guidance from Britain and Ireland which has been covered in the review, namely ADB [5], BS 9991:2015 [9], its 2021 draft revision [10], Building Regulations Technical Guidance Document B (TGDB) [11], and the Building Standards Technical Handbook: Domestic (BSTH) [12].

Compartment size

Compartmentation is a common means of limiting the spread of fire and smoke and thus a way to reduce the risk associated with a fire hazard [13]. As such, limiting the area of a flat is a common approach for reducing the severity of the hazard by minimising the extent of fire spread.

ADB places no explicit restriction on compartment sizes but does effectively preclude open plan designs where travel distances are in excess of 9 m and / or where inner rooms are not a kitchen, laundry or utility room, dressing room, or bathroom. In contrast, BS 9991:2015 facilitates open plan design with inner rooms, but this is limited to flats not exceeding 16 m by 12 m (192 m²). This maximum compartment area broadly aligns with BSTH in Scotland, which suggests its guidance is only applicable to dwellings with an individual storey less than 200 m². TGDB places no restrictions on the compartment size for the flat.

Travel distances

A common approach to internal flat arrangements is to restrict the distance occupants may have to travel in the flat before reaching a separate compartment or place of relative safety [2]. The main purpose of limiting the travel distance is to minimise the distance occupants may need to travel in a fire or smoke affected environment, therefore minimising the time that they may be subject to untenable / toxic conditions [14].

In ADB, where a protected entrance hall is provided, the flat should have a single direction of travel restricted to 9 m from the flat entrance to the furthest door of a habitable room. Where a protected entrance hall is not provided and there are no inner rooms outside of those mentioned previously, the total travel distance should not exceed 9 m. BS 9991:2015 applies similar restrictions, but the travel distance can be extended to 20 m with the provision of an automatic suppression system and an automatic fire detection and alarm system. The recommendations of TGDB are largely consistent with BS 9991:2015, while BSTH does not appear to place restrictions on travel distances within a flat.

Location of cooking facilities

It has been suggested that fires from cooking facilities (stovetops, kitchen hobs, ovens, etc.) may pose a threat to dwelling occupants when the facilities are in proximity to an escape path [15]. This is owing to the increased likelihood of fires starting in the kitchen of a dwelling compared to other rooms [16]. As a result, guidance in Britain and Ireland typically recommends that cooking facilities should be located such that they do not prevent escape when involved in a fire. A common approach to this is to enclose the kitchen in smoke-retarding construction and / or provide a protected entrance hall (discussed previously).

However, in the case of open plan arrangements where the kitchen is not enclosed in smoke-retarding construction, ADB, BS 9991:2015, and BSTH do not provide an explicit and quantitative recommendation of how this should be achieved. To address this, the draft BS 9991 has introduced a recommended positioning of the cooking facilities relative to the means of escape (Figure 1) with a distance of 1.8 m to the egress route and 2.1 m from the flat door. TGDB in Ireland introduced a similar recommendation in 2016, albeit it does not differentiate between the distance to the escape route and the distance to the door, i.e., it applies a distance of 1.8 m universally. Spearpoint et al. [1] have estimated that the 1.8 m separation distance is equivalent to approximately a 99^th percentile tolerable heat flux.

Figure 1 – Draft BS 9991 [10] recommended distances of cooking facilities from open plan flat escape routes.

Summary of International Standards

Table 1 provides a summary of the standards reviewed for the three factors of: limitations of compartment size; maximum internal travel distance in a single direction (noting that a value for multiple directions has not been presented herein); and the location of the cooking facilities.

The review presents a heavily condensed version of the recommendations of these standards, where guidance on flat design can be distributed across several pages of a standard. The information presented in Table 1 should therefore not be interpreted as a comprehensive representation of fire safety recommendations / requirements for flat design.

Table 1 – Comparison of all standards assessed.

Discussion and Conclusions

Fire safety standards and guidance in Britain and Ireland place significant emphasis on how flats are internally arranged, with further restrictions placed on open plan arrangements, i.e., where protected entrance halls are not provided or arrangements where kitchens are not enclosed in smoke-retarding construction. In particular, consideration is given to compartment size, travel distances, and location of cooking facilities, all of which have defined restrictions.

In the professional experience of the authors, these restrictions can impose challenging spatial constraints on designers when addressing flat internal layouts. This requires fire engineers to regularly carry out analyses to support arrangements which deviate from guidance recommendations [29]. These analyses can be subject to a great degree of debate and scrutiny with authorities having jurisdiction and fire engineers carrying out third-party reviews, often without a clear understanding of the benefit the analyses provide with respect to life safety.

In contrast, it appears that fire safety standards and guidance outside of Britain and Ireland place much less emphasis on the internal planning of flats, with the main recurring restriction being internal travel distances (typically around 20 to 40 m for a single direction), where the internal travel distance recommendations can be greater in international standards when compared to the guidance in Britain and Ireland. Most international standards reviewed in this article either place no restrictions on flat compartment sizes or allow for large enclosures (500 m²+), while only one standard outside of Britain and Ireland reviewed in this article comments on kitchen enclosures and the location of cooking facilities.

It could be postulated that there are several reasons for why standards outside of Britain and Ireland provide fewer restrictions on internal flat design:

·         To afford greater spatial flexibility for designers, and to assist in capturing day-to-day wants or needs of the end user beyond considerations of just fire safety.

·         Depending on the local laws, regulations, and freehold / leasehold agreements, the internal layout of a flat could be subject to the discretion of the occupier, allowing for modifications to the arrangement over the lifetime of a building. With this in mind, standards could omit restriction on internal planning to accommodate for this possibility.

·         In the absence of a more thorough review of the literature, there may be limited evidence to suggest that placing limitations on flat designs significantly improves the level of safety a building / flat achieves in comparison to the lack of flexibility in which it provides the designer or occupier.

With respect to the final point mentioned above, it has been discussed elsewhere [30] that the number of fatalities in the UK resulting from accidental dwelling fires by cooking appliances is relatively low compared to other sources of ignition. West Midlands Fire Service (WMFS) fire incident data [31] between 2009 and 2021 indicates that while 44% of accidental dwelling fires in this geographic area were caused by cooking appliances, they contributed a lower 13% of fire-related fatalities. For kitchen fires more broadly, 53% of total incidents in the West Midlands have resulted in 18% of fatalities. A recent Home Office review of fire-related fatalities and casualties across England from 2010 to 2019 indicates that the most common source of ignition for fatal fires is smokers’ materials followed by cigarette lighters, with cooking appliances sitting third and contributing a similar number of fatalities as space heating appliances [32]. The rate of fatal fires is estimated to be 1.2 for cooking appliances with other electrical appliances, candles, heating appliances, matches, and smokers’ materials all produce a higher rate (from 1.3 up to 18.3). However, it is worth noting that the majority (66%) of ‘severe casualty’ fires in England (where an individual goes to hospital and has at least an overnight stay) occur within the kitchen, with the most common source of ignition (22%) in these incidents being the cooking appliance.

One hypothesis for the above observations is that UK fire safety guidance for kitchens and cooking appliances is largely working as intended to reduce the consequence of the hazard. An alternative hypothesis is that the severity of the hazard associated with cooking appliance fires is less likely to result in fatality than other dwelling fire hazards. However, the observation of kitchen fires producing fewer fatalities appears to be consistent around the world, where design limitations on cooking facilities are less strict. Hutchison and Hostikka [33] indicate that “while kitchen or cooking area fires continue to be a leading area of origin in home fires around the world, these fires are less likely to result in fatalities than those in living rooms and bedrooms”. In this context, the latter hypothesis appears to hold strong even in jurisdictions where restrictions on internal dwelling design are minimal, although it is acknowledged that this is a very broad assessment of the data.

Ultimately, from the review of international standards and the brief summary of fire incident data above, it may be argued that fire safety design guidance in Britain and Ireland places too great a priority on how flats are internally arranged, particularly in situations where suppression and automatic fire alarm and detection systems are provided. Questions therefore arise as to whether a review or amendment to UK guidance is warranted to better accommodate other factors in the design of residential buildings.

References

[1]          M. Spearpoint, C. Hopkin, and D. Hopkin, ‘A probabilistic thermal radiation analysis of cooking hob separation distance in open plan kitchens’, Fire Mater., 2022, doi: 10.1002/fam.3101.

[2]          C. Hopkin, M. Spearpoint, D. Hopkin, and Y. Wang, ‘Fire safety design of open plan apartments in England’, Archit. Eng. Des. Manag., pp. 1–20, 2020, doi: 10.1080/17452007.2020.1719812.

[3]          BSI, ‘British Standard Code of Practice CP3: Chapter IV: Part I: 1971, Code of Basic Data for the Design of Buildings, Chapter IV Precautions Against Fire, Part 1. Flats and maisonettes (in blocks over two storeys)’, The Council for Codes of Practice, British Standards Institution, 1971.

[4]          Department of the Environment and the Welsh Office, ‘The Building Regulations 1991, Approved Document B (1992 edition)’, 1992.

[5]          HM Government, ‘The Building Regulations 2010, Approved Document B (Fire Safety) Volume 1 (2019 edition incorporating 2020 and 2022 amendments)’, 2022.

[6]          J. Fraser-Mitchell and C. Williams, Open plan flats: assessing life safety in the event of fire. IHS BRE Press on behalf of the NHBC Foundation, 2009. Accessed: Sep. 17, 2019. [Online]. Available: https://www.nhbcfoundation.org/publication/open-plan-flats/

[7]          C. Davis, S. Murphy, and D. Hopkin, ‘Open plan apartments - revisiting risks in light of contemporary demands’, International Fire Professional Journal, vol. 18, pp. 33–35, 2016.

[8]          BSI, ‘BS 9991:2011 Fire safety in the design, management and use of residential buildings. Code of practice’, BSI, London, 2011.

[9]          BSI, ‘BS 9991:2015 Fire safety in the design, management and use of residential buildings. Code of practice’, BSI, London, 2015.

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