4.1 Pipe Sizing, Protection & Permitted Locations

Sizing: The Installer Builds What the Designer Calculated

NFPA 99 requires piping systems to be designed and sized to deliver the required flow rates at the utilization pressures. Sizing belongs to the designer, but the installer is responsible for installing exactly the sizes on the approved drawings and for knowing the code minimums:

Why it matters: the verifier later measures performance at each outlet (Section 7.4). A 50 psi gas outlet must deliver 3.5 SCFM (100 SLPM) with no more than a 5 psi pressure drop. Oxygen and medical air outlets serving Category 1 spaces must also handle a 6 SCFM (170 SLPM) transient for 3 seconds. A vacuum inlet must draw 3 SCFM without pulling an adjacent inlet below 12 in. HgV. An undersized branch or a field substitution shows up as a failed flow test.

Field changes that look harmless but are not

• Replacing a specified 3/4 in. vacuum branch with 1/2 in. to match outlet drops (below the vacuum minimum)
• Adding long offsets that the designer did not account for
• Feeding new outlets from an existing branch without design review

Any of these can cost the outlets their required flow. Changes go back to the designer and the AHJ.

Protection

NFPA 99 requires piping to be protected against freezing, corrosion, and physical damage:

• Exposed piping in corridors and other areas where it could be struck by carts, stretchers, portable equipment, or vehicles must be protected, for example with guards or by routing it out of harm's way.
• Piping underground within buildings or embedded in concrete floors or walls must be installed in a continuous conduit. Copper cast directly into concrete cannot be inspected or replaced, and it is exposed to corrosion and stress.
• Buried piping outside buildings has its own rules for depth, frost, backfill, and marking (Section 4.2).

Where Piping May and May Not Go

Risers may run in pipe shafts if they are protected from physical damage, excessive heat, corrosion, and contact with oil.

Prohibited locations. Piping may not be installed in:

1. Kitchens
2. Stairwells
3. Elevator shafts
4. Elevator machine rooms
5. Areas with open flames
6. Areas with electrical service equipment over 600 volts
7. Areas prohibited by NFPA 70 (the National Electrical Code)

Exceptions: piping may run in rooms that house medical air compressor supply systems and medical-surgical vacuum pump supply systems. It may also run in rooms containing secondary distribution circuit panels and breakers rated 600 volts or less.

Shared trenches and tunnels. Medical gas piping may share a service trench or tunnel with fuel gas, fuel oil, electrical, and steam lines and similar utilities only if:

• the space is ventilated, naturally or mechanically, and
• the ambient temperature around the medical gas piping is limited to 130°F (54°C) maximum.

Oil exposure. Medical gas piping may not be placed where it is subject to contact with oil, including possible flooding areas in the case of a major oil leak. This rules out, for example, the space beneath an emergency generator's day tank, where a spill could reach the pipe.

Zoning and Story Boundaries

Location rules extend to how zones are laid out (Chapter 5). Piping on the patient side of a zone valve may serve outlets only on the same story. All columns, hose reels, ceiling tracks, pendants, booms, and similar special installations must be on the patient side of their zone valve. Do not route a zone's branch through the floor to pick up outlets on the level below, even if that saves pipe.

Hoses and Flexible Connectors

Hoses and flexible connectors, metallic or nonmetallic, must be no longer than necessary. They must never penetrate or be concealed in walls, floors, ceilings, or partitions, because a hidden hose cannot be inspected or replaced. They must also have a minimum burst pressure of 1000 psi gauge. Section 4.2 covers metallic flexible joints used for expansion and seismic movement.

Installation by the Manufacturer's Instructions

Individual components such as valves, outlets, alarms, and manufactured assemblies must be installed according to the manufacturer's instructions. Those instructions must include what is needed for proper operation, testing, and maintenance, and copies are left with the system owner. Following the instructions is part of meeting the code, not an optional extra.