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Fire Safety of Buildings

The Fire Safety Documents have changed in many ways since the Building Act 1991 with many amendments as the relatively new science of fire engineering develops. Fire safety requirements to new and alterations to existing buildings
 
A Review of the Building Code Requirements

All new buildings must comply with the performance requirements of the Building Code that includes fire safety per Clauses C1 to C4 found in the first Schedule of the Building Regulations.

These clauses are:

C1: Outbreak of fire,
C2: Means of escape,
C3: Spread of fire and
C4: Structural stability during fire.

With regard to alterations to existing buildings, the Building Act 2004: Section 112 Alterations to existing buildings requires that after the alteration, the building will -

a) comply, as nearly as is reasonably practicable with the provisions of the building code that relate to -
 
(i) means of escape from fire
(ii) access and facilities for persons with disabilities

b) continue to comply with the other provisions of the building code to at least the same extent as before the alteration.

Additionally, where there is a ‘change of use’ or subdivision Section 115 and 116 of the Act respectively require that the building will -
 
(i) comply, as nearly as is reasonably practicable with every provision of the Building Code that relates to -

c) means of escape from fire, protection of other property... and fire rating performance and
 
(i) continue to comply with the other provisions of the building code to at least the same extent as before the change of use/ application for subdivision.

The most significant difference with respect to change of use or subdivision is the requirement for buildings to comply with respect to protection of ‘other property’ (land or buildings) from the effects of fire. Fire protection of the affected property or properties may be required irrespective of whether the other property has a building on it or not.

Interpretation of ‘Change of Use’

Change of use is not so much as may be interpreted in layman’s terms but relates more specifically and in particular to fire safety implications. Examples are:
  • a ‘change in the use’ of an industrial building from a low risk occupancy to one with a higher fire risk eg: a change of stored flammable products on racks to over 3m in height, a change resulting in an increase in the occupant numbers (occupant load).
  • an office space use being changed to retail or storage, or a change resulting in an increase in the occupant load eg: office to retail.
  • a residential use being changed eg: to include a home occupation or the addition of a ‘granny flat’ or ‘minor unit’.
Interpretation of Subdivision

Subdivision can include unit or strata titling of a building, boundary redefinitions, or subdivision of land with existing buildings that may result in issues regarding fire separation from relevant boundaries (horizontally and vertically). This can apply to residential situations where the subdivision or unit titling results in an existing or proposed building being located within 1m of a relevant boundary.

Alterations to Existing Buildings

The first schedule of the Act relating to building work not requiring a Building Consent has been amended to allow a lot more work to be done without the need for a Building Consent. The list of items may be found on the dbh website www.dbh.govt.nz.

However work that does require a Building Consent will require the building to be upgraded for fire egress and disabled access. For example adding a new toilet facility to the ground floor of a building will constitute an alteration and will require a Building Consent. This therefore means the whole building would have to be upgraded for fire egress and disabled access.

New or amended fit out of an office would not require a building consent if it can be shown that the fit out did not affect structural and/or fire safety issues. Principally, with respect to fire safety, this relates to safe egress as far as alterations to existing buildings is concerned ie: that the fit out does not compromise safe egress in any way such as increasing escape route lengths beyond what is acceptable, or blocking off existing escape routes etc. Where such spaces in a building are fitted with active warning systems eg: smoke or heat detectors or sprinklers new partitioning may compromise the effectiveness of detectors and if this is the case a Building Consent would be required to cover the relocation or additional of detectors for example.
 
As nearly as is reasonably practicable?

Alterations to existing buildings that trigger a requirement for a Building Consent will require the building to be upgraded for means of escape from fire. This requires a review of the fire safety for the building in relation to the current Building Code requirements (as nearly as is reasonably practicable).

Using the argument that something is not ‘reasonably practicable’ to do to meet compliance can’t be related to cost implications only and an argument against meeting current code provisions must consider a cost/benefit balance.

It is important to appreciate the regulatory/legal regime pertaining to the Building Act and the Building Code. The current regime is pyramidal in hierarchy with the Act at the top under which lies the Building Code and Regulations. All of these are law i.e.: they must be complied with regarding any new building work. Embodied in the Building Code are the Acceptable Solutions eg: C/AS1 the Fire Safety documents, Verification Methods eg: B1/VM1 and Alternative Solutions.  All of these are non-mandatory however one or the other or a combination of these must be adopted to achieve code compliance. Alternative Solutions are often used in fire engineering and require any approach used to be backed up by sound fire engineering principles, risk analyses, sensitivity analyses etc. in order to show the alternative solution adopted meets the performance requirements of the Building Code. This is not always an easy task!!

Specific fire engineering design allows economies in many cases over the Acceptable Solutions as, like other non-specific design methodologies, more accurate and hence economical case specific designs can be adopted. (See C/AS1 : Paragraph 1.1.2)
 
Typical Fire Safety Issues

We cannot stress enough the importance of including the fire safety assessment for a project in the very early stages of the design process as the fire safety requirements can often be onerous and may dictate many of the design considerations (architectural, structural, electrical, mechanical, water supply etc.).

Common fire safety issues include:
  • Mezzanine floors in buildings. Fire safety often requires a Type 4 automatic fire alarm system with smoke detectors and manual call points, fire and smoke separation etc particularly if the floor area of the mezzanine is greater than 20% of the ground floor area. Mezzanine floors and their supporting structure generally require a FRR (fire resistance rating) of no less than 30 minutes (in some cases 15 minutes).
  •  
  • External walls requiring fire rating (and post fire stability) where close to relevant boundaries. In the case of residential building this is generally (but not always) when the external wall is within 1m of a boundary. In the case of industrial buildings the separation distances required for no fire protection may be large ie: greater than 15 or 16m in some cases or alternatively the allowable % of unprotected areas may be small where buildings are close to boundaries ie: most or all of the wall may require fire rating.
  •  
  • The requirement to vent roof for fire in large firecells.  Roof venting primarily helps to reduce the time a fire burns and hence reduces the S rating ie: the FRR of external walls. GRP roof lights and similar are now considered unacceptable and PVC or polycarbonate more appropriate although alternative mechanical venting systems are an option.
  •  
Changes in the Fire Safety Documents
  •  
The Fire Safety Documents have changed in many ways since the Building Act 1991 with many amendments as the relatively new science of fire engineering develops. More changes are due with potentially a whole new design approach with respect to the current documents.

One change that affects most buildings now is the requirement for visibility in escape routes and in particular emergency lighting in the event of a fire. Emergency lighting is required in all exitways, at all changes in level in a building and from the point where the escape route length to the nearest exit exceeds 20m. Exitways are a defined term meaning smoke or fire protected means of escape such as horizontal and vertical protected paths or safe paths.

Once out of the building, occupants must be able to get to a safe place. Access to the safe place must meet the accessibility requirements of the building code. The safe place must be remote from the building so that occupants are not at risk from the effects of a fire eg: smoke, flame and thermal radiation. This would require the safe place to be some distance from any non fire protected external walls of the building.

Over the past year Airey Consultants have completed more than 200 fire safety reports for a vast variety of residential, industrial and commercial clients.
 
2.0 Disabled access requirements:

In addition to fire safety issues, Building Act 2004: Section 112 Alterations to existing buildings, requires alterations to a building to comply with respect to facilities for persons with disabilities. This would also require the building to have the appropriate number of accessible sanitary facilities.
 
Access Routes

NZBC Acceptable Solution D1/AS1 ‘Access Routes’ lists the requirements for accessible routes including stairs, ramps passages etc. At least one access route approaching a building shall have features to enable people with disabilities to have access to the internal space of a building served by the principal access. Generally, these requirements are:

Ramps: gradient no more than 1 in 12; width no less than 1200mm; landings no less than 1200mm long and 750mm maximum rise between landings or;

Stairs: Rise = 150mm min., 180m maximum; tread 310mm min., 400mm maximum; open risers not permitted, clear width 900mm; rise between landings 2.5m.

Doors: Minimum width = 760mm clear opening; passages clear width = 1200mm min.

The Building Regulations 1992: Clause D1 – Access: D1.3.4 (c) requires a building to include a lift where:
 
(i) a building is four or more storeys high,
(ii) a building is 3 storeys high and has a design occupancy of 50 or more persons on the two  upper floors,
 
  • a building is two storeys and has a total design occupancy of 40 or more persons on the upper floor (this equates to a floor area of 400m2 or more based on and occupant density of 0.1 people/m2 which is typical of an office type of occupancy)

Where the building has independent access directly to outside ground level no lift may be required in the building if independent access to each level complies with the accessible requirements of the Building Code.

Disabled access does not necessarily mean wheel chair access and can include people with other disabilities whether temporary or permanent such as sight impairment for example.

With respect to the disabled access door thresholds comply with D1/AS1 ie: the maximum threshold step should not exceed 20mm.

NOTE: Single steps within or giving access to buildings in not permitted in all but SH and SR Purpose Group occupancies ie: Detached dwellings and residential apartments or townhouses.
 
Accessible sanitary facilities

Building Code Acceptable Solution G11/AS1 requires sanitary facilities in occupied buildings. G1/AS1: Paragraph 4.0, People with Disabilities, provides an acceptable means of providing such facilities within a building. Alterations to a building will only require the accessible facilities to be upgraded/ provided.

Accessible facilities need not be in addition to those for other building occupants ie: they can be shared facilities eg: one facility for all but it must meet accessible dimensional and sanitary fixture requirements.

Table 1 of G1/AS1 Personal Hygiene lists the number of sanitary fixtures required for staff with disabilities.  In the case of offices, shops etc.1 x WC and 1 x hand basin is required for staff numbers from 1 to 300. Showers are not required for commercial uses but are for dirty industrial occupations however these need not be accessible if less than 10 people are employed.

Accessible toilet facilities need not be provided in industrial buildings where no more than 10 people are employed (G1.3.4).

Details of the requirements for accessible facilities are covered in G1/AS1 Figures 5 to 8.

 
Roger Twiname
MIPENZ (Civil & Structural),
CPEng


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