Britomart Tunnel
Structural Steel Intumescent Coating

Deep beneath Auckland’s CBD, the structural steel supporting KiwiRail’s Britomart tunnel needed its passive fire protection renewed, a job that could not simply be scheduled around normal working hours because the corridor remains a live rail environment. Any loss of fire protection on structural steel is a serious risk below ground, and reinstating it meant the coating system had to be rebuilt correctly the first time, with dust and debris fully contained so nothing escaped into the tunnel or affected rail operations.

BlastOff sandblasted the steel members to the cleanliness required before recoating, clearing away existing contamination and leaving a surface the intumescent system could bond to properly. Intumescent paint was then applied to each member to the specified loading, with dry film thickness measured and recorded at every stage to build an accurate asset record for KiwiRail. This kind of intumescent fire-proofing work depends on getting the preparation right, since any residual rust or contamination beneath the coating can compromise how it performs if it is ever called on.

Facility owners managing steel in confined or operational environments, whether a tunnel, plant room or basement car park, should expect any passive fire scope to be planned around access windows and containment as carefully as the coating itself. A proper scoping conversation should cover the extent of steel requiring protection, the current condition of any existing coating, and how access and containment will be managed while the space stays in use. Working hours and the sequencing of access windows need to be agreed upfront, since below-ground and infrastructure environments rarely allow the same freedom of movement as an open commercial site.

For structural steel that also needs surface preparation or a wider protective system, pairing sandblasting with the fire protection scope keeps preparation and coating consistent across the whole steel network being treated, with thickness records tied to each stage giving the asset owner a clear reference for future inspections.