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What are the main applications of Automist?

  • Meeting building regulations
  • Elective fire safety upgrade


1) Meeting building regulations

When Automist is used to meet Building Regulations, the purpose and coverage requirement is often defined in a guidance document Approved Document B (as a replacement for a BS 9251 system), BS 9991 or a fire engineering report.

Common reasons a BS 8458 system is required:



Area protected by Automist

Other requirements

Guidance support

Loft conversion 

E.g. A new storey is added through conversion to create a storey above 4.5m 

Any open plan areas connected to the escape route 
  1. Provide a fire resisting partition (minimum REI 30) and door (minimum E 20) to separate the ground storey from the upper storeys. The door should allow occupants of the loft room access to a first storey escape window. 

  1. Separate cooking facilities from the open-plan area with fire resisting construction (minimum REI 30). 

Note. Some AHJs opt for enhanced detection (i.e. in all rooms of the property LD1) over kitchen and first floor separation as they believe the kitchen fire risk is overstated and the door between the first and ground will typically be propped open.   

Approved Document B, Vol 1, 2019 edition, Section 2.23 


BS 9991 Section 6.5 (see 11.2, Table 2) 

New Build Dwelling

Houses with two or more storeys more than 4.5m above ground level 


Either (a) or (b):  

a. Protected stairway – a stair separated by fire resisting construction (minimum REI 30) at all storeys, that complies with one of the following: 

i. Extends to a final exit. 

ii. Gives access to a minimum of two ground level final exits that are separated from each other by fire resisting construction (minimum REI 30) and fire doorsets (minimum E 20). 

Cavity barriers or a fire resisting ceiling minimum EI 30) should be provided above a protected stairway enclosure. 

b. Alternative escape route – a top storey separated from lower storeys by fire resisting construction (minimum REI 30) and with an alternative escape route leading to its own final exit. 

Approved Document B, Vol 1, 2019 edition, Section 2.6 


BS 9991 Section 6.4 (see 11.2, Table 2) 

Open-plan flat 

E.g. A flat with bedrooms off one of the living areas, where the floor is above 4.5m from the ground outside 


Grade D LD1 fire alarm and fire detection system in accordance with BS 5839-6:2013 

  1. The size of the open-plan flat should not exceed 16 m × 12 m. 

  1. Open-plan flats should be situated on a single level only. 

  1. The ceilings within the open-plan flat should have a minimum height of 2.25 m. 

  1. The kitchen should be enclosed in open-plan flats having an area exceeding 8 m × 4 m. Cooking appliances in open-plan flats having an area smaller than 8 m × 4 m should not be adjacent to the entrance of the flat. 

BS 9991 Section 9.7 (see 11.2, Table 2) 

Blocks of flats with a top storey more than 11m above ground level

Should be fitted with a sprinkler system throughout the building in accordance with Appendix E. 


Sprinklers should be provided within the individual flats, they do not need to be provided in the common areas such as stairs, corridors or landings when these areas are fire sterile. 

For buildings over 30m BS 9991:2015 states a watermist system conforming to DD 8458 is ‘Not applicable’ in Table 2. The FIA has produced guidance for ‘Additional Requirements for Watermist Systems Protecting High-rise Buildings’ over this height. Given the contradiction in guidance it is advisable this is brought to the attention of anyone proposing the use of a BS 8458 in buildings over 30m.  Approved Document B, May 2020 Amendments, Section 7.4 


The system may also be used to meet building regulations as a compensatory measure. If, for example, Automist is being used to compensate for a lack of fire doors, this should be supported by a fire engineering report from a chartered engineer.

2) Elective fire safety upgrade

In this case, Automist is being used to improve levels of fire safety. The system is not however a requirement for Building Regulations or general minimum statutory life safety standards. Therefore the design, performance and implementation of Automist is completely at the client's discretion and are not governed by statutory prescriptive requirements. In this case, the performance and/or operation of the suppression systems are not relied upon for adequate minimum standards of safety within the accommodation.

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Disclaimer: This information is not intended to be a comprehensive guide to all of the aspects of the building regulations but rather a useful source of background information. Whilst every care has been taken to ensure that the contents of this document are correct at the time of publication, it should never be used as any form of substitution for the guidance documents. Plumis shall be under no liability whatsoever in respect to the contents of this document. It should be noted that there may be specific additional requirements dependent upon local authority building regulations and/or fire authority.