Modular operating theatres: scope, air and pressure standards

By ZY Cleanroom · Updated 2026-11-01 · Sources at the end of the page

What is in scope

A typical package covers the panel envelope, floor finish, hermetic or sliding doors, a ceiling air diffuser with terminal filters, return grilles, a control panel and a pass-through hatch.

Agree in writing who supplies the air-handling unit, ducting, medical gases, surgical lights, pendants, isolated power and the link to the building management system. These items are often outside the panel contractor's scope.

Modular construction is a choice, not a rule. NABH's 2018 guidance says a modular operation theatre is not a mandatory requirement under any NABH programme, so the owner decides.

Air and pressure values by region

These are design values for the operating room itself. Check the current edition for your project.

Worked example: airflow for one theatre

HTM 03-01 standard layout 1 uses a 165 m³ theatre at 22 or more air changes per hour. The total supply is 1.01 m³/s, about 3,640 m³/h, made up of 0.73 m³/s primary air and 0.28 m³/s from the lay-up room. Size the AHU for your own room volume, not this example.

Other national classes

Germany's DIN 1946-4:2018 sorts rooms into room class I, with Ia and Ib, and room class II. China's GB 50333-2013 defines clean classes 5, 6, 7, 8 and 8.5 by particles of 0.5 µm and larger. Class 5 is above 350 and up to 3,500 particles per cubic metre.

Pressure and door design

UK guidance sets pressure room by room: theatre 25 Pa, scrub 25 Pa and lay-up preparation room 35 Pa (HTM 03-01 Part A, standard layout 1). A convertible suite can run the theatre at the same pressure as its corridor for infectious cases, with no air cascading out (para 8.125).

ASHRAE 170 Addendum y, approved 22 September 2026, requires a documented risk assessment before operational adjustments to space ventilation.

Put these in the room data sheet

State the filter grade. HTM 03-01 lists EPA E10, 85% at the most penetrating particle size, to E11, 95%, as typical for ultra-clean theatre terminals (Table 10). NABH asks for HEPA at 99.97% down to 0.3 µm and supply air at ISO 5 at rest.

State the airflow tolerance. HTM 03-01 gives the design airflow +10% and −0% as the normal commissioning tolerance and expects independent validation on the client's behalf (paras 11.29 and 11.16).

ASHRAE 170 lists MERV 16 as the minimum filter efficiency for operating rooms and does not allow air recirculation by room units. NABH asks for the filtered area to extend one foot beyond the table on all sides, and for 18 ± 2 °C in joint replacement theatres.

Who approves the room

Your health regulator or accreditation body judges the facility, not the contractor. The contractor builds to your room data sheet and supplies test results. The owner keeps the responsibility. To have a room list reviewed, send it to ZY Cleanroom, a cleanroom design-and-build contractor with its own panel factory in Tianjin, China.

Related guides

• Cleanroom wall and ceiling finishes: coving, sealants, joints and stainless steel
• Hardwall vs softwall cleanroom: how to choose
• Cleanroom airlock design: bubble, cascade and sink
• Paper Honeycomb Cleanroom Panels for Walls and Ceilings
• Turnkey cleanroom contractor
• Room list builder

Sources

• NHS England, Health Technical Memorandum 03-01, Specialised ventilation for healthcare premises, Part A (published 22 June 2021; checked 31 October 2026)
• ANSI/ASHRAE/ASHE Addendum y to Standard 170-2025, Ventilation of Health Care Facilities, Table 7-1 (approved 22 September 2026; checked 31 October 2026)
• NABH, Revised Guidelines for Air Conditioning in Operation Theatres (issue 4, November 2018; checked 31 October 2026)
• DIN 1946-4:2018-09, Ventilation and air conditioning, Part 4: Ventilation in buildings and rooms of health care, contents list (checked 31 October 2026)
• GB 50333-2013, Architectural technical code for hospital clean operating department, terms 2.0.7 to 2.0.11 (English preview; checked 31 October 2026)