A utility tunnel is one confined space with two work patterns. Routine inspection means many access points, short stays and a rotating cast of people. Maintenance — hot work, desilting, cable pulling — keeps a crew inside for hours. Equipment sized for one pattern fits the other badly: drag the full kit and the full permit process through every walk-through and the routine gets skipped within a week; run maintenance on an inspection-grade setup and the protections the standard requires are simply not there.
What inspection needs: know who went in, and whether anything changed
For walk-through rounds, two capabilities carry the load. Entry control at access points, where an authorised tag is recognised and the passage is logged automatically — the record builds itself instead of depending on discipline. And fixed gas monitoring at the sections that earn it: sump wells, low points, poorly ventilated runs, watched continuously and escalated when a reading goes abnormal. Neither capability needs a crew-sized deployment; both need to be always on.
What maintenance needs: the full sequence, point by point
Maintenance follows the sequence ventilate, then test, then enter. Gas monitoring is laid out to the sampling-point rules of GB 46768-2025: at least three detection points vertically, no more than 8 m apart, near and far points horizontally. Long sections extend coverage by cascading units along a cabled bus — 1,000 m in total, 20 m between nodes as standard, up to 100 m where the geometry allows — because radio does not propagate through hundreds of metres of reinforced concrete. Entrants wear smart wristbands watching heart rate and blood oxygen, and gas alarms, wearer abnormality and the camera view all return to the monitoring station at the entrance, which carries a backup battery rated for 6–8 hours through a power cut.
One platform, two records
Fixed monitoring, entry control, the mobile monitoring station and the wristbands can be procured in stages as the tunnel program allows; what matters is that all of them report into one management platform. Inspection logs and maintenance files stay separate as records but retrieve from one place — which is how the audit question “show me what happened in that chamber” gets answered without archaeology.
When one kit is enough
Small tunnels with a handful of chambers do not automatically need two tiers of equipment. If the same crew does both the walking and the working, one mobile set can serve inspection rounds and maintenance jobs alike — but entry logging and work permits stay mandatory in both cases. The tier that cannot be merged is the paperwork, not the hardware.
List the program before the purchase order. Inspection frequency, the maintenance plan, the number of chambers and the access points — that list decides how many of each front-end to buy. Our LSM3000-series linear monitoring system supports the cascaded layout and unified platform behind this arrangement, in municipal and power tunnels alike.