Why does HTM 02-01 allow two pipes in separate trenches?

It is the HTM 02-01 (2026) alternative where an underground duct cannot have removable covers: two pipes at least 2 m apart, each sized for 100% of the design flow and isolable individually, with LVAs at each end for individual or dual feeding.

How often should an outdoor oxygen pipeline be inspected?

HTM 02-01 (2026) says external exposed pipeline should be inspected at least annually (Part B), and Part A asks for pipelines in enclosed ducts with steam or water services to be inspected annually.

How is oxygen piped from a plant in a separate building?

Q: How is oxygen piped from a PSA plant or tank in a separate building to the hospital, buried or overhead, and how is the line protected?

Under HTM 02-01 (2026), the NHS England guidance, external pipe runs should be avoided where practicable; buried lines run in drained ducts at least 450 by 450 mm with removable covers, or, failing removable covers, as two full-flow pipes in separate trenches at least 2 m apart, with line valves at building entry and exit.

How is oxygen piped from a PSA plant or tank in a separate building to the hospital, buried or overhead, and how is the line protected?

HTM 02-01 Part A (2026 edition), NHS England's guidance for medical gas pipeline design and installation, gives the rules for the pipe between a supply plant and the building it serves. This page covers the pipeline only, not where the PSA plant or liquid oxygen tank itself should stand.

Underground

In a duct: an appropriately drained duct measuring at least 450 mm by 450 mm, fitted with removable covers.
Where removable covers are not possible: two pipes in separate trenches at least 2 m apart, each able to carry 100% of the design flow and each isolable on its own, with line valve assemblies (LVAs) at each end so the building can be fed by either pipe or both. One or more different gas pipelines can share each trench.
The route should be marked on the surface and shown clearly on the site layout drawings.

On walls and across roofs

On external walls, the pipes should be protected up to the height at which they could be damaged, for example by vehicles, with galvanised steel profile covering the full width of the pipes plus at least 50 mm on each side. The armour stands 50 mm off the surface so the pipes can be inspected by eye, and it should be readily detachable for closer inspection. Similar protection against foot traffic is needed where pipes cross horizontal surfaces and roofs, and fully boxed-in pipework follows the rules for ducts. Against lightning, the pipework should run within a 60-degree cone beneath the lightning conductor; across a roof, a copper lightning conductor runs along the top of the pipework cover and is bonded to it.

Valves, earthing and inspection

LVAs, lockable open or closed, are provided at the connection to any source of supply, at the emergency inlet port, and where the pipeline enters and leaves a building.
All medical gas pipelines should be bonded to the main earth terminal at building entry and exit.
Medical gas pipes should be routed away from natural gas pipelines where flammable gas could accumulate after a leak, and should not run in enclosed ducts with other services where they cannot be inspected; where they share ducts with steam or water services, they are inspected annually because leaks can leave chloride deposits that corrode them.
HTM 02-01 Part B asks for external exposed pipelines to be inspected at least annually, looking for damage such as abrasion, flattening and corrosion caused by chemicals, water leaks or bird droppings.

For the emergency inlet port itself, see what an emergency supply inlet is.