The number of confined space monitors a site needs is decided by sampling geometry, not by the number of spaces. GB 46768-2025 — the safety technical code for confined space operations, in force from 1 May 2026 — sets out the layout, and once it is laid point by point, the equipment count follows arithmetically.
The vertical rule: three points, 8 metres apart
Vertical spaces take at least three detection points. The upper and lower points sit within 1 m of the top and the bottom respectively, intermediate points distribute evenly with no more than 8 m between them. Where the vertical run is under 2 m, two points — top and bottom — are sufficient. In practice, the deep cases are the ones that bite: a degassing tower or a deep wet well sampled at one point will miss the stratification the standard is written for.
The horizontal rule: near and far
Horizontal spaces — cable trenches, culverts, long galleries — take at least two points: one near, one far. The near point sits no less than 0.5 m from the entrance, the far point at least 2 m in. The two points answer different questions: the near point sees what the entrant meets first, the far point sees whether the far end is worth walking to.
From points to units
Unit count follows from the point count. Spaces with many points need online monitoring equipment that accepts several sensor heads simultaneously — and the code expects a spot reading every 15 minutes while work is under way, which is precisely what manual logging misses on a busy job. Our LSM3000-series monitoring station connects multiple gas-detection units inside and outside the space at once, so a vertical-plus-horizontal layout goes up in one deployment. Entry monitoring is a separate count: one set per access point, whatever the space count is.
The ordering mistake to avoid
The configuration lists we issue follow a fixed order: sensor heads from the sampling points first, entry-control equipment from the number of entrances second. Buying complete units by space count skips the middle step, and the way it usually surfaces is an audit finding: a layout that looks plausible until someone counts the points the standard actually requires.
Send us the spaces, not the budget. List each space with its depth or run length and its access points, and we will return the sampling-point layout, the sensor head count and the entry-control count — a configuration that survives the audit rather than a quote that survives until delivery.