A world apart?

Performance based requirements for both the United Kingdom and New Zealand are based on similar life safety and property protection objectives. These objectives can be achieved using performance based design or by following the prescriptive guidance. However, the prescriptive guidance that can be used varies greatly between both countries.

Several documents can be used for the design of buildings in both countries, and this article focuses on the differences between the Approved Documents B and C in the UK and New Zealand respectively.

Often regarded as having one of the most innovative and least prescriptive fire engineering approaches in the world, New Zealand was one of the first countries to actively adopt the use of performance based fire engineering designs. The first prescriptive based Approved Documents were published in 1995, with the latest major amendments occurring in June 2001 – Approved Document C: Fire safety and acceptable solutions C/AS1.

The Approved Documents outline the performance requirements of the Building Regulations, including life safety and protection of other property. The acceptable solutions are the prescriptive solutions to achieve the performance requirements. Alternatively, a performance based fire engineered solution can be used to demonstrate that the building will satisfy the performance requirements.

Once one is familiar with the fire safety documents, they are reasonably easily applied. Furthermore, through the iterative update process, the acceptable solutions now incorporate designs that previously would have been considered alternative solutions. To some degree this has reduced the opportunities for fire safety engineers to add value. However the acceptable solutions are still too generic for most buildings and aspects of performance-based design are still required. Recent statistics quoted by the Wellington City Council, (a territorial authority encompassing New Zealand’s capital city and approximately 250 000 people), indicate that approximately 80% of fire safety designs submitted for buildings incorporate some aspect of performance based design or alternative solution. Given this, there remains scope for fire engineers to add some value during the design process of most buildings.

Some amendments to the acceptable solutions have been made based on construction cost or common construction problems rather than life safety risk assessment or actual fire hazard with respect to protection of other property. This is partly due to the acceptable solutions being developed by the Building Industry Authority, which is part of the Ministry of Economic Development. This approach leaves fire safety engineers little scope for alternative design when performance based modelling shows higher requirements than the minimum requirements of the acceptable solution should be provided to properly mitigate risk.

Although performance based design is encouraged in New Zealand, the comparatively less stringent requirements of the prescriptive acceptable solution, leads to reduced opportunities. Due to this, architects and building services engineers may offer fire engineering services as an add-on. This has the effect of lowering the fees of fire engineering services, and can, as a consequence, lower the quality of service provided to the client.

When compared to New Zealand, the UK prescriptive guidance is awkward, ambiguous and complicated to use. There are several documents to consult for the outline of the fire safety design – predominantly Approved Document B and the BS 5588 series are used and these can contradict each other. Designers can choose which document to use – their decision will be based on which gives the best design for the building. There are then additional area regulations to contend with, such as the Section 20 of the London Building Acts and the Hampshire Act. One may also need to consult specialised fire safety documents for discussions not outlined in the above, such as the Health Technical Memorandum documents for hospitals and HMO documents for houses of multiple occupancies.

Much of the design of UK buildings is based on the judgement of the designer and/or the building control inspector. There is little firm guidance in many of the documents regarding, for example, if a fire alarm system is required, or if it is required, to what level – ie L1-L5, ranging from full coverage to escape routes only.

Thankfully, the UK fire documents are currently being revised under the Regulatory Reform Act in an attempt to rationalise and simplify existing fire safety legislation, however it is unknown how successful this will be.

The general cost and scope of design fees in the UK is typically greater than in New Zealand. There is, therefore more opportunity to investigate fire and egress modelling. Fire engineering fees are often sufficient to allow the engineer greater time to design the building in detail. Additionally, the profession is still an emerging discipline in the UK and the number of people working as fire engineers is relatively small.

Specific differences

So what are some of the major differences between the two approaches? In terms of fire resistance rating requirements, there is a move in New Zealand to increase the reliance on fire alarm systems and early warning as compensation for decreased requirements for passive protection. For example, the maximum fire rating required for any building protected with sprinklers and smoke detectors, regardless of use or occupant load, for heights up to 58 m, is 30 minutes.

In the UK, any non-residential building greater than 30 m in height requires sprinklers and a 120-minute compartment fire rating provided. However, the extent of smoke detection, (if any), will depend on the use of the building.

Where a building is greater than 18 m tall, or has a basement deeper than 10 m in the UK, there is a requirement for a fire-fighting shaft to assist fire service access to the building and to carry out fire fighting activities. There is no such requirement within the New Zealand regulations. The fire fighters are required to use the general access stairs for entry to the building, and there is no provision of a fire fighting lift for high-rise buildings, or use of a lift for escape. Additionally, lower fire ratings implemented throughout New Zealand buildings allow predominantly for the escape time for the building’s occupants and therefore provide less protection to the fire fighters after evacuation is complete.

Increases in travel distances are permitted in New Zealand where automatic fire alarm systems are installed in the building. The percentage increase depends upon the alarm installed, (heat or smoke detector or sprinkler), and the use of the building. For example, an office building with sprinklers can have travel distances increased by 100%, allowing 48 m where there are dead ends and 120 m where there is more than one direction of escape. This is significantly greater than the UK limitations of 18 m and 45 m for dead end travel and total travel distance respectively, regardless of the fire safety systems provided in the building. Some increases in travel distances due to alarms, use and management structure are proposed for the revised BS 9999 series, which are yet to be formally released.

New Zealand was one of the first countries to actively adopt the use of performance based fire engineering designs.

Another major difference between the New Zealand and UK Approved Documents is the requirement for flats and maisonettes to have internal protected halls where the travel distances within a flat are greater than 9 m. The UK restrictions on travel distances within the flat and the protected entrance hall are theoretically useful, however in practice, the fire doors are predominantly wedged open and their purpose negated. There are no such restrictions imposed on the internal layout of flats within New Zealand, except that the maximum travel distances of 24 m must not be exceeded. This allows greater architectural scope to designers and property developers on internal apartment design.

When sprinklers are installed within New Zealand buildings, the advantages often outweigh the cost of the installation. Some areas of cost savings and architectural freedom are:

• Decrease of internal fire ratings by half, (to minimum of 15 minutes in some cases).
• Increase of the permitted openings on external walls by 100%.
• Decrease of fire ratings to other property by half.
• Increase of the permitted travel distances by 100% for office, retail and assembly buildings, and by 50% for sleeping purpose groups.
• No requirement to discount the largest exit when assessing escape widths.
• May permit a single stair, where two stairs would be required if not sprinklered, (dependent on building height).

In the UK, the only dispensation allowed for under the regulatory documents when sprinklers are installed is the increase in openings to external walls. Some other allowances may be provided through discussion with local approval authorities. The Office of the Deputy Prime Minister has indicated that further dispensations due to sprinklers will be included in the next amendment of Approved Document B.

Residential case study

A simple residential case study is summarised in the table 1. This outlines the typical requirements for an eight storey residential building, (ground plus seven levels), with building escape height of 21 m, and the requirements that would be imposed by the Approved Documents in both New Zealand and UK. The table also demonstrates the considerable difference in design that installation of a sprinkler system will have on the fire safety requirements of the building.

Strengths and weaknesses

New Zealand fire safety philosophies are based on an active fire alarm system, with less reliance on passive separations. The UK fire safety approach is based on compartmentation and containing the fire to a small area. Their evacuation strategy is such that the number of people affected by a fire alarm is kept to a minimum, where possible.

So which approach is safer? Which is most cost-effective? There have been several revisions of the New Zealand documents since they were first implemented in 1995 and these have been updated to include what are considered the best and most cost-effective solutions. As fires occur or more information is made available, changes in the documents reflect the current thinking in areas of fire safety.

The New Zealand approach allows greater flexibility in design with reduced requirements for internal compartmentation, yet imposes greater requirements on the fire alarm system. In addition, with lower requirements on separation of areas with fire resistant compartments, there are less inherent provisions for property protection.

The UK approach can limit the alternatives permitted in design, especially with respect to residential developments, and construction cost can be higher. However, fire services costs and ongoing maintenance and monitoring cost are subsequently lower.

With most fatal fires in both countries occurring in residential dwellings, where there are limited restrictions imposed on the buildings, it is difficult to ascertain which approach is better. In both countries, the impact on fire engineering is up to the individual design team and the persons involved.

Having now worked both in the UK and New Zealand, I appreciate that neither system is perfect and that each system has different strengths. While the New Zealand prescriptive guidance is easier to use and is more user-friendly to designers and developers, it can be restrictive to the scope of fire engineering that can be applied. Challenging projects do arise, however as every building consent (required for almost any building works in all buildings except residential dwellings) requires a fire report, this can lead to a high turnover of small projects that can lack challenge or variability.

However, in the UK the scope and magnitude of the projects to be involved with far exceeds that of New Zealand. Although this is largely due to the general population and economy of the country, the restrictions of the prescriptive guidance and detail required from Building Control leads to greater involvement in each project, increased level of justification of a fire engineering design and more opportunities to deviate from the prescriptive guidance. 

Kathryn Lewis is a fire engineer with Hoare Lea Fire, Hoare Lea Consulting Engineers. Previous to that she worked for three years as a fire engineer with Holmes Fire and Safety in Wellington, New Zealand.