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CROSS Safety Report

Horizontal mains used as a solution to meet vehicle access requirements

Report ID: 1268 Published: 21 May 2024 Region: CROSS-UK


Clients are proposing horizontal mains as a solution to meet the firefighting vehicle B5 access requirements of Approved Document B (ADB). Building control bodies are increasingly accepting these proposals.

Key Learning Outcomes

For designers, planning authorities and building control bodies:

  • The use of horizontal mains as a compensation feature for the lack of fire engine access should not be routinely used
  • Guidance regarding fire brigade access is not only to limit hose distances. It also enables a range of factors including quick deployment of firefighting personnel and essential equipment

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This section contains the Full Report submitted to CROSS and describes the reporter’s concerns or experiences. However, the text has been edited for clarity, and identifiable details have been removed to ensure anonymity and confidentiality. If you would like to know more about our secure reporting process, or submit a report yourself, please visit the reporting to CROSS-UK page.


A fire and rescue service has reported the increasing use of horizontal mains by developers and designers to meet fire engine access requirements, as stated in Approved Document B, B5, Section 15, Volume 2 - Buildings other than dwellings.

Fundamentally, a fire vehicle should be able to access a defined percentage of the building perimeter, or it should be able to park within a 45-metre hose laying distance of every point in the building.

The reporter gives examples of incidents where Approved Inspectors (AI) have adopted a horizontal main to satisfy the guidance within ADB, but in reality, attending firefighters would be unlikely to use it.

ADB Volume 2, Clause 16.3 allows fire mains to be used where the access requirements detailed above cannot be met.

What constitutes a fire main is not defined in ADB, however the guidance is clearly written with vertical risers in mind. Clause 16.3 directs the reader to Clause 16.4 which says that the outlet should be in a protected stairway or protected lobby. Additionally, Clause 15.4 (a) says that inlets should be on the face of the building.

Furthermore, Clause 16.5 states that guidance on the design and construction of fire mains is given in BS9990. Clause 4.2.1 states that, 'Any proposed use of horizontal fire mains should be discussed and agreed with the local fire and rescue service. Horizontal dry fire mains (no vertical pipework) are typically not a practical design solution'.

Any proposed use of horizontal fire mains should be discussed and agreed with the local fire and rescue service

The reporter describes how these designs are increasingly being accepted by planning authorities and building control bodies, against fire authority advice during consultation stages.

The acceptance appears to be based upon the view that the horizontal main mitigates the extended hose laying distances. This position takes no account of whether the main would actually be used by attending firefighters, nor any other aspects of firefighting that underlie the reasons for adequate vehicular access to a building, such as:

  • Preventing delays due to increased travel distances for firefighters, particularly carrying breathing apparatus
  • Preventing delays due to having to carry rescue equipment such as breaking in gear, hose lines, and ladders
  • Preventing the restriction of the full use of facilities provided by a pumping appliance, for example hose reels. Horizontal mains tend to be designed for connection to lay flat (70-millimetre hose) which is more cumbersome to work with and may delay firefighting

Once signed off by building control, there is little a fire service can do to address the issue, without utilising the Regulatory Reform (Fire Safety) Order 2005.

Furthermore, once the horizontal main is installed it needs to be regularly maintained and tested by the building owner and kept well drained to reduce legionella risks. This can be difficult for long sections of horizontal main.

The reporter suggests that building control bodies be made aware of the issues for fire services in using horizontal mains to address vehicle access requirements. They also suggest that ADB should be updated to address this issue.

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This is, unfortunately, a regularly encountered issue by fire and rescue services (FRSs) when conducting statutory consultations with building control bodies (BCBs), and the reporter identifies some key points. 

The provision of horizontal mains is often seen as a solution to compliance; however, it is only as far as considering the provision of water. This completely misses other factors, as the reporter identifies.

It is worth highlighting functional requirement B5 of the Building Regulations 2010 (as amended) and what is actually said:

'Access and facilities for the fire service B5. (1) The building shall be designed and constructed so as to provide reasonable facilities to assist fire fighters in the protection of life. (2) Reasonable provision shall be made within the site of the building to enable fire appliances to gain access to the building.'

It is clear this is more than just the provision of water. Of additional note, is the Secretary of State's view on the intention of B5 (from ADB):

'Provisions covering access and facilities for the fire service are to safeguard the health and safety of people in and around the building. Their extent depends on the size and use of the building. Most firefighting is carried out within the building. In the Secretary of State’s view, requirement B5 is met by achieving all of the following.

a. External access enabling fire appliances to be used near the building. b. Access into and within the building for firefighting personnel to both: i. search for and rescue people ii. fight fire. c. Provision for internal fire facilities for firefighters to complete their tasks. d. Ventilation of heat and smoke from a fire in a basement.

If an alternative approach is taken to providing the means of escape, outside the scope of this approved document, additional provisions for firefighting access may be required. Where deviating from the general guidance, it is advisable to seek advice from the fire and rescue service as early as possible (even if there is no statutory duty to consult).'

This provides further clarity that access and facilities for the FRS are there to fight the fire and conduct search and rescue activity. It also clarifies that they need to be ‘near the building’. 
Where a horizontal main is provided for water, this does not address the need for firefighters to then travel the extended distances from their appliances and having to carry and locate all equipment that may be needed. 

As identified by the reporter, this places additional resource limitations on attending crews, increases the physiological effects on the firefighters, and delays firefighters being able to establish safe systems of work to commence operational activity to those that need it most.

the use of horizontal mains should not be routinely used to compensate for poor vehicular access

Not all buildings have firefighting shafts on their face. There is some inevitable horizontal section to get from the inlet, at the face of the building, to the rising/falling main in the firefighting shaft. However, normal vehicular access (that is, at a maximum of 18 metres to the riser inlet, ADB vol 1 Clause 13.5a) and limiting the internal travel distances to the firefighting shaft at access level (as in BS9999 20.2.2) reduce the distances firefighters and gear have to travel.

It should also be noted that horizontal mains are an acceptable feature included in the design of many healthcare buildings incorporating a hospital street.  Notwithstanding this, the use of horizontal mains should not be routinely used to compensate for poor vehicular access. It is important to have discussions with FRS before the building control sign-off of their use, reviewing areas such as:

  • Exhausting methods of improving vehicular access
  • Signage of inlets so that the area that they serve is immediately obvious to the fire service
  • Other mitigation measures to compensate for delays in firefighting 
  • Maintenance and drainage

if the dry main is buried in the ground, there may be no way to drain it. This creates a corrosion and Legionella risk

The maintenance issue is also of importance where these additional measures are considered, as in the FRS experience, these measures are generally the first to fall foul of a lack of regular testing and maintenance, be it through a lack of understanding of their provision or due to budgetary pressures. In addition, if the dry main is buried in the ground, there may be no way to drain it. This creates a corrosion and Legionella risk.

As the enforcing authority of the Regulatory Reform (Fire Safety) Order 2005 (as amended), the FRS can take action under Article 38, Maintenance of measures provided for protection of firefighters. However, this is not much use when identified at an operational incident. 

Also of note, is that the variation instead of sprinklers was put in for dwelling houses in BS9991 for backland developments. The sprinklers are there to offset the additional time for FRS intervention due to the longer travel. One FRS has held firm on its position regarding the use of extended horizontal mains, but it is concerned about the expansion of permitted development which may result in more schemes with poor FRS access provisions due to commercial to residential change of uses.

Building regulations determination SB-007-001-007 discusses a similar issue. While determinations are specific to their respective circumstances and cannot be applied as if a precedent has been set, the wider issues are identified and discussed.

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