fire sprinkler systems and the changes to bs 9251

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1Canute LLPFIRE SPRINKLER SYSTEMSBS 9251 : 2014 - AN INTRODUCTION

Hydraulic Calculation Software for the fire protection industry

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2BS 9251 : 2014CHANGES TO THE STANDARD

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http://www.canutesoft.com

Topics covered Major changes to the standard Cautionary notes Preliminary work and consultation

Category of system Design – only the following

Minimum design parameters – table 2 Head spacing Minimum head requirements

http://www.canutesoft.com/tag/5-residential.html

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Introduction The Bsi technical review panel FSH/18/2 – BS 9251 has

taken 18 months of deliberation All major stakeholders have consulted including BRE,

BAFSA, Fire & Rescue Service, RSA, Water Undertakings and Building Control

The committee received and reviewed 328 comments to the proposed standard at DPC stage.

The standard is comprehensively different to the previous and will take some adjustment

BS 9251:2014 standard will be implemented on October 31st 2014 and the 2005 edition will be withdrawn.


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Major changes

The term ‘residential’ and ‘domestic’ have been removed in favour of categories 1, 2 and 3.

The system design is now based on the discharge density and the number of heads operating.

The standard recognises the one size cannot fit all and talks about ‘special circumstances’.

Where the system is used for ‘compensatory features’ additional requirements may be needed.

Standard talks about ‘vulnerable people’.


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Cautionary note BS 9251:2014 is a code of practice not a standard. It offers guidance and recommendations. It should not be quoted as a ‘specification’ document. If you deviate from the standard you are expected to

be able to justify your course of action. The BS is to be used by appropriately qualified and

experienced people.


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Cautionary note

Compliance with the British standard cannot confirm immunity from legal obligations. If you are legally obliged to do something then this is implied

and may not be referred to within the standard An example would be you must always comply with water

regulations and this standard does not detail all the regulations.

The new standard is considerably different and you need to read it all – DON'T CHERRY PICK


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Consultation

Water undertaker Fire authority Licensing authority Building control Insurer(s) of the building &

contents The client The list is not limited!

The standard requires you consult at an early stage (enquiry or design?)

Type of occupancy Compensatory features Vulnerable people Mixed use


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What we need to consider

Is BS 9251:2014 suitable for the risk [4.1] Category of system [4.3] & [Table 1]

If the risk is not listed or the building is more than 45m height then the AHJ(s) should be consulted we may need a BS EN 12845 system?

DO we have ‘compensatory’ features [4.4] DO we have ‘special circumstances’ [4.5] DO we have ‘venerable people’ [3.31] & [4.5] Do we have a ‘fire strategy or risk assessment’ [5.4] &

[Table 1]


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Special circumstances

Extend duration of water supply

More robust water supply Redundancy Fire service infill

Increasing Design Density and/or Increase Area of operation

In some circumstances, enhanced performance, reliability and resiliencearrangements should be provided, if an assessment shows them to be necessary.Where appropriate, the designer should consult the relevant AHJ(s).

High fire loadings Older buildings Atria Fire engineered solutions Mixed use buildings Secure accommodation Vulnerable people


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Vulnerable people

“people who are at greater risk from fire because they are unable to easily evacuate without assistance, or who have a higher than average likelihood ofexperiencing a fire, or a combination of the two”

BS 9251:2014 [3.31]

The BS 9251 tells us in Annex B, in some detail what it considers as vulnerable people and what addition measures may be required.


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Compensatory feature

Older buildings New buildings which cannot meet

the necessary requirements for fire appliances

Loft conversions – adequate means of escape

“There are occasions when a suppression system is used as a means of demonstrating compliance with building regulations or to compensate for, or overcome, circumstances where a building is unable to achieve compliance with guidance issued in support of building regulations.”

BS 9251 : 2014 [4.4]

Consultation with AHJ’s Agree the Category of system &

design density May need a fire risk strategy Consider Special circumstances [4.5] Recorded agreed measures on the

compliance certificate


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Category of system

Type 3

Type 2

We can determine the category form Table 1, if the occupancy is listed and the building is less than 45m

If it not then the AHJ(s) must be consulted to agree which category is applicable (if any), if ‘additional measures’ are required or if a BS EN 12845 system is more appropriate.


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Category of systems – Table 1Category

Description

1 Single family dwellings such as: A)

• Individual dwelling house• Individual flat or maisonette• Transportable home

House of multiple occupation (HMOs) A) B)

Bed and breakfast accommodation A) B)

Boarding housesBlock of flats < 18m in height A) C)

2 Block of flats > 18m in height D)

Small care homes E)

3 Care homesNursing homesResidential rehabilitation accommodationDormitoriesHostels

You need to check the footnotes. They can change the category


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Category of system : Type 1and modifiers

Single family dwelling Type ?Vulnerable

people


Risk assessment

HMOs

Bed & breakfast

Boarding houses

Vulnerablepeople

More than 2 floors or

more thanfive lettable

rooms

Type 2

Type ?

Which ever is the highest


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Type ?

Blocks of flats < 18m

Vulnerablepeople

Communal roomsor corridors

require protection Type 3

Total floor area is less

than 2400m2


Risk assessment

Which ever is the highest


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Type 3Block of flats > 18mCommunal rooms

or corridorsrequire protection

Small residential care homes

More than 10 residents Type 3

Sheltered and extra care housing

Communal roomsor corridors

require protection Type 3

>18m & < 45m in height


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Category of system : Type 3

Dormitories

Residential care homes(more than10 residents)

Hostels

If the risk is outside that listed in Table 1 then you may need to look at an enhanced systems ‘Special Circumstances’ or BS EN 12845 may be more appropriate.


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Minimum design parameters - Table 2

Category of System

Min design density mm/min

No of sprinklers Min duration of supplyminutes

1 2.04 A) 1 or 2 102 2.80 B) 1 or 2 303 2.80 C) 2 or 4 D) 30

Again we have a lot of footnotes to read and understand.

Table 2 gives the minimum design parameters and can by modified if the system is installed for ‘compensatory features’, ‘special circumstance’ or ‘fire strategy / risk assessment’.


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The footnotesA) Where a sprinkler system is installed as a compensatory feature (see 4.4), the minimum design discharge densityshould be increased to either:

a) 2.80 mm/min for a single head operation, or 2.04 mm/min through each sprinkler operating simultaneously

up to a maximum of two sprinklers in a single area of operation; orb) 4 mm/min for single head operation, or 2.80 mm/min through each sprinkler operating

simultaneously up toa maximum of two sprinklers in a single area of operation.

The increased level of discharge density needed [a) or b) above] should be agreed with the AHJ prior toinstallation, based on the risk identified.B) Where a sprinkler system is installed as a compensatory feature (see 4.4), the minimum design discharge densityshould be increased to 4 mm/min for single head operation, or 2.8 mm/min through each sprinkler operatingsimultaneously up to a maximum of two sprinklers in a single area of operation.C) Where a sprinkler system is installed as a compensatory feature (see 4.4), the minimum design discharge densityshould be increased to 4 mm/min for single head operation, or 2.8 mm/min through each sprinkler operatingsimultaneously up to a maximum of four sprinklers in a single area of operation.D) Where communal areas/corridors are managed areas and considered to be sterile within a fire strategy report orwith agreement by the AHJ, the number of design sprinklers may be limited to two in these areas only.


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Footnote A – Type 1 category

A) Where a sprinkler system is installed as a compensatory feature (see 4.4), the minimum design discharge densityshould be increased to either:

a) 2.80 mm/min for a single head operation, or 2.04 mm/min through each sprinkler operating simultaneouslyup to a maximum of two sprinklers in a single area of operation; orb) 4 mm/min for single head operation, or 2.80 mm/min through each sprinkler operating simultaneously up toa maximum of two sprinklers in a single area of operation.

The increased level of discharge density needed [a) or b) above] should be agreed with the AHJ prior toinstallation, based on the risk identified.

Footnote A gives is applicable to Type 1 system when the systems is installed for compensatory features and gives you a choice of a) or b) but it must be agreed with the AHJ.


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Footnote B & C – Type 2 & 3 category

B) Where a sprinkler system is installed as a compensatory feature (see 4.4), the minimum design discharge density should be increased to 4 mm/min for single head operation, or 2.8 mm/min through each sprinkler operating simultaneously up to a maximum of two sprinklers in a single area of operation.C) Where a sprinkler system is installed as a compensatory feature (see 4.4), the minimum design discharge density should be increased to 4 mm/min for single head operation, or 2.8 mm/min through each sprinkler operating simultaneously up to a maximum of four sprinklers in a single area of operation.

Footnote B & C is applicable to Type 2 & 3 system when the systems is installed for compensatory features, it looks complicated but its not. The only difference is that you need a minimum of 4 mm/min from the most remote sprinkler head and 2.8 mm/min from the sprinkler in your area of operation

You will need two sets of calculations to prove this.


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Footnote B & C – Type 2 & 3 categoryFootnote B & C is applicable to Type 2 & 3 system when the systems is installed for compensatory features, it looks complicated but its not. The only difference is that you need a minimum of 4 mm/min from the most remote sprinkler head and 2.8 mm/min from the sprinkler in your area of operation

You will need two sets of calculations to prove this.

MRH

Based on a Type 3 systems we would need to prove what we can get 4 mm/min from the MRH and 2.8 mm/min from all 4 heads.


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Footnote D – Type 3 category

D) Where communal areas/corridors are managed areas and considered to be sterile within a fire strategy report or with agreement by the AHJ, the number of design sprinklers may be limited to two in these areas only.

Footnote D tells us that if areas such as corridors which are consider as sterile in the fire strategy and with agreement with the AHJ can have the number of sprinkler in operation reduced to two.

This could reduce the total water demand for the systems and therefore you may have a smaller water supply.


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Sprinkler head coverage

Maximum sprinkler coverage 25m2

Maximum spacing between heads 5.5m or 1/2 a design spacing from any wall or partition

Minimum distance between sprinkler should be 2.4m Only sprinklers heads in accordance with BS 9252

should be used unless agreed with the AHJ


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Sprinkler heads and flow rate

Minimum head pressure of 0.5 bar Minimum k-factor of 40 lpm/min/bar0.5 (mm/min)

The minimum k-factor will precluded the standard been used for water mist systems


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Extent of sprinkler protection

Bathrooms < 5 m2

Cupboards with floor area < 2 m2

Attach buildings and crawl spaces

Sprinkler protection should be provided in all parts of the premises. However,unless required by a fire strategy or risk assessment, the following may beexcluded:

Uninhabited loft/roof voids


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Compartments5.5 m

3.6

m

A compartment is an area enclosed by walls and a ceiling, where any openings are not more than 2500 mm in width and either:

A. A lintel depth of not less than 200mm or

B. A single opening of not more than 900 mm in width without a lintel

Compartments are important as it will determine the number of heads in operation, the required flow and pressure for the systems and the tank size.


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CompartmentsAs this opening is wider than 2.5 m in width we will need to take the sprinkler is then staircase in to consideration.

So we have the kitchen, dining room and the staircase as one compartment.

But the maximum number of sprinkler s in operation is limited to:

2 for Type 1 & 2 or4 for Type 3


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Compartments

3.0 m

3.6

m

This area is divided by a wall with a opening 2.0 m wide which has a lintel 200 mm in depth.

2.5 m

2.0

m Therefore the two rooms can be considered as separate compartments.

Sprinkler A and B can be considered to be in separate compartments and calculated separately


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Compartments

3.0 m

3.6

m

This area is divided by a wall with a opening 1.5 m wide with no lintel.

2.5 m

1.5

m Therefore the two rooms must be considered as the one compartments.

We will need to calculate sprinkler A and B as both are in the area of operation.


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fire sprinkler systems and the changes to bs 9251

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