Description

This document describes a method for determining safe separation distances for adjacent buildings. A fire in one building carriers the risk of spreading to an adjacent building.

Current methods for determining separation distances in New Zealand are based on Acceptable Solution C4/AS1 Appendix C, in the New Zealand Building Code. It is assumed in C4/AS1 that the neighbouring building is the same distance from the boundary as the building under consideration. In many cases, therefore, it yields non-conservative results, and lacks flexibility.

The method proposed in this document allows an alternative means of determining safe separation distances. It allows the critical incident radtion to be varied for various faade materials, and different radiation source intensities to be specified. The effects of changes to existing buildings resulting from renovations can also be evaluated.

This method of determining safe building separation distances is particularly useful for limiting fire spread in isolated locations and where there are limited fire-fighting resources.

Scope

The procedures described in this document can be applied in the following situations:

1. Dertermining a minimum separation distance between two buildings to prevent fire spread;
2. Determining a minimum distance to boundaries where a neighbouring building does not yet exist;
3. Determining the incident radiation received on a neighbours building;
4. Determining the maximum size of openings permitted on the owners buiilding if the separation distance is fix;
5. Checking the safety of existing building situations, which can be improved by:

• fitting fire windows to either building;
• reducing the number of and/or size of openings;
• raising the level of critical radiant flux for ignition of existing claddings, recladding or overcladding; and
• installing external drenches.

In all the above cases it is important to check the level of radiation in both directions.