Most operation theatre problems are decided long before the first wall panel goes up. They’re decided on a drawing, in a meeting where someone says, “Let’s keep it a little smaller,” or “We can sort out the air handling later.” Then a NABH assessor walks in, or your first orthopaedic surgeon asks why the room feels cramped, and the fix costs far more than the original decision would have.
If you’re planning a new hospital or upgrading an OT in Delhi, Delhi NCR or anywhere else in India, this guide takes you through the design in the order we’d actually do it. It’s written for owners, directors and administrators, so you don’t need an engineering background. You’ll finish with a clear brief to hand to your architect and your modular operation theatre manufacturer.
The short version: design a NABH-ready modular OT in this order.
- Decide your OT type (Type A or Type B).
- Fix the size and number of OTs.
- Plan zones and movement.
- Lock the air system.
- Choose seamless finishes and doors.
- Plan the services inside the room.
- Build validation and maintenance in from day one.
- Review the layout against a checklist before you sign off.
What NABH actually requires (and what it doesn’t)
Before you design anything, know the rulebook. The National Accreditation Board for Hospitals & Healthcare Providers (NABH) publishes Revised Guidelines for Air Conditioning in Operation Theatres, and these drive most OT design decisions. Hospital standards are in the NABH Accreditation Standards for Hospitals, 6th Edition, effective 1 January 2025.
Two things surprise most hospital owners.
A modular OT is not mandatory. NABH states that a modular operation theatre is not a mandatory requirement under any programme, and it’s left to the hospital whether to install one. So why do most hospitals building new OTs choose modular anyway? Because the parameters NABH asks for, such as pressure, particle count, air changes and temperature, are much easier to achieve and keep with a sealed, factory-built system than with brick-and-plaster construction.
Not all OTs have the same requirements. NABH splits them into two types:
| Type A OT | Type B OT | |
| Used for | Neurosciences, joint replacement, cardiothoracic, transplant | Ophthalmology, day-care surgery, all other basic surgical disciplines |
| Air quality at supply grille | Class 100 / ISO Class 5 | Class 1000 / ISO Class 6 |
| Total air changes per hour | Minimum 20 | Minimum 20 |
| Fresh air component | Minimum 4 air changes | Minimum 4 air changes |
| Positive pressure | Minimum 2.5 Pa | Minimum 2.5 Pa |
| Temperature | 21°C ± 3°C (18°C ± 2°C for joint replacement) | 21°C ± 3°C |
| Relative humidity | 20–60% (ideal 55%) | 20–60% |
| HEPA filter (99.97% at 0.3 micron) | To be provided | May be provided |
Source: NABH Revised Guidelines for Air Conditioning in Operation Theatres (2018).
Also check which NABH programme you’re applying under. The air conditioning guidelines are described as desirable under all programmes, but not mandatory for small healthcare organisations or those on pre-entry certification. Confirm this with your NABH consultant before you set your specification.
Decide your OT type and surgical mix:
Start with a list, not a drawing. Write down:
- Which specialties will operate here in year one and in year five
- How many surgeries per day you expect
- Whether any of your cases fall under Type A (joint replacement, neuro, cardiac, transplant)
This one decision changes your air system, your cost and your room size. A hospital that starts with general surgery and plans to add joint replacement in two years should design for Type A now. Upgrading the air system later means opening ceilings and shutting the OT.
NABH tip: Joint replacement has its own temperature target (18°C ± 2°C). If ortho is on your roadmap, say so to your vendor before the HVAC is sized.
Fix the OT size and the number of theatres:
A commonly cited standard size for a general OT is about 20 ft x 20 ft with a 10 ft ceiling height, which appears in infection control training material from the Delhi Government’s CNBC hospital. Treat that as a starting point, not a rule. Cardiac, neuro and orthopaedic cases with large equipment (C-arm, microscope, navigation systems) usually need more room.
Three questions to settle size:
- What is the biggest piece of equipment that will ever come into this room?
- How many people will be in the room at once, including residents and observers?
- Will you ever want a hybrid or image-guided setup here?
For the number of OTs, think about throughput and emergencies: elective list, emergency cases, and a buffer for when one OT is down for maintenance or validation. Many hospitals in Delhi NCR forget that last point and end up cancelling lists during routine servicing.
Design tip: Leave ceiling height and structural allowance for pendants and laminar panels. Check the available floor-to-slab height before you finalise the OT location, especially in older buildings.
Plan zones and traffic flow:
An OT suite is more than the operating room. It’s a sequence of spaces, and people, patients, instruments and waste should move through it in one direction. Typical zones are:
- Outer zone: reception, patient transfer, staff change rooms
- Clean zone: pre-op, scrub area, sterile store
- Aseptic zone: the operating room itself
- Disposal zone: soiled utility and waste exit
What to get right:
- Staff and patients enter from the clean side, and soiled material leaves by a separate route
- The scrub station sits where the team passes before entering the OT. See our guide to sizing your OT scrub station (1-bay, 2-bay or 3-bay)
- Sterile storage is close to the OT, so staff aren’t walking long distances with open trays
- Doors are few and well-sized, because every door opening disturbs pressure
[Image suggestion: simple OT suite floor plan with the four zones colour-coded. Alt text: “Modular operation theatre layout showing clean, aseptic and disposal zones”.]
Lock the air system, the heart of NABH compliance:
If you remember only one step, make it this one. Air handling is where most NABH findings and most OT infections trace back to. From the NABH guidelines:
- Dedicated AHU per OT. Each OT should have its own air handling unit. A shared AHU for multiple OTs is allowed only with a backup plan, redundant fans and UPS and DG power.
- Unidirectional airflow over the table at a face velocity of 25–35 feet per minute.
- HEPA filtration with a filter area extending at least one foot beyond all sides of the OT table.
- Positive pressure of at least 2.5 Pa at all times, including non-operating hours.
- No window or split ACs in any OT. NABH specifically excludes them because they only recirculate air and have spots where microbes can grow.
- Outdoor air intake away from DG exhausts, lab exhaust vents and parking areas.
- Blower running 24x7, with air changes reducible to 25% at night through a variable frequency drive, as long as pressure is maintained.
To understand why airflow class matters, read our explainer on the importance of Class 100 airflow in a NABH-compliant OT. The global benchmark is similar. The CDC’s guidelines for environmental infection control in healthcare facilities call for positive pressure and at least 15 air changes per hour in operating rooms, and NABH sets a higher bar of 20.
Delhi NCR note: Winter smog and summer dust put heavy loads on pre-filters. Specify easy-access filter panels and plan the 30-day pre-filter cleaning that NABH recommends. A design that’s hard to service will get serviced late.
Choose seamless finishes and sealed doors:
Infection control is as much about surfaces as air. Look for:
- Smooth, non-porous wall and ceiling panels with no open joints where dust can settle
- Coved corners and flush fittings that wipe clean easily
- Flooring that is seamless and chemical-resistant
- Hermetically sealed doors that hold pressure. Read more on advanced OT doors for surgical cleanrooms
Ask every vendor for panel material specifications, joint details and door sealing methods in writing. This is where a cheap proposal usually cuts corners.
Plan the services inside the room:
Once the shell and air are fixed, decide what goes in the OT. Mark these on the layout early, because ceiling and wall positions are hard to change later:
- Medical gas outlets from your medical gas pipeline system (MGPS) for oxygen, nitrous oxide, air and vacuum
- Pendants: know the difference between a surgeon pendant and an anesthesia pendant, and place each where the team works
- OT lights: see OT lights explained: specs, pricing and how to choose
- OT table: choose by specialty. Here’s how surgeons choose the right OT table
- LED X-ray viewers for ortho and trauma lists. See why surgeons prefer LED X-ray viewers
- Power and backup: UPS and DG support for the AHU and critical equipment
- Nurse call and communication: a nurse call system for pre-op and recovery
Build validation and maintenance into the design:
NABH expects the OT air system to be validated every 6 months. That includes:
- Temperature and humidity check
- Air particle count
- Air change rate calculation
- Air velocity at the filter outlet
- Pressure differential against adjoining areas
- HEPA filter integrity testing
Design with this in mind. Leave test ports, service access and space for the instruments. And plan an AMC/CMC at the time of purchase, not after the first breakdown. A beautiful OT that isn’t maintained will not stay NABH-ready.
Review the final layout with this checklist:
Before you sign off, make sure you can answer yes to each of these:
- Have we confirmed Type A or Type B for every OT?
- Is the room size right for our largest equipment and team?
- Is there one-way movement from clean to disposal?
- Does each OT have its own AHU, or a documented backup plan?
- Are HEPA coverage, 20 total air changes, 4 fresh air changes and 2.5 Pa positive pressure all in the written specification?
- Is the outdoor air intake away from DG exhaust and parking?
- Are all surfaces seamless and the doors hermetically sealed?
- Are gas outlets, pendants, lights and power points marked on the plan?
- Is there a 6-monthly validation plan and an AMC?
- Do we have a written handover and documentation list for the NABH assessor?
Designing for Delhi NCR and across India:
NABH standards are national, so a compliant OT in Gurugram is built to the same parameters as one in Jaipur, Lucknow or Bengaluru. But local conditions change how you apply them:
- Delhi, Gurugram, Noida, Ghaziabad, Faridabad: Plan for severe pollution months and extreme summer heat. Specify generous pre-filtration, accessible filters and reliable backup power. Many sites here are retrofits in existing buildings, where NABH permits options such as a ceiling-suspended AHU or a DX unit with AHU, as long as the same air parameters are met.
- Approvals: Check your state and local requirements early, such as nursing home or hospital registration, fire safety clearance and radiation safety approvals if you’ll use C-arms or X-ray. Your consultant should confirm what applies in your location.
- Tier-2 and tier-3 cities: Service access matters more. Choose a vendor who can commission, validate and support the OT after handover, not only supply it.
MedGenz designs, manufactures and installs modular operation theatres for hospitals across Delhi NCR, Haryana, Punjab, Rajasthan and Uttar Pradesh, and delivers pan-India. See where we’ve worked on our projects page.
5 design mistakes to avoid
- Designing for today’s surgeries only. Specialties get added. Plan for them.
- Treating the air system as an add-on. It’s the core of the OT.
- Sharing one AHU across OTs with no backup. NABH allows it only with redundancy and validation evidence.
- Ignoring service access. If filters are hard to reach, they won’t be cleaned on time.
- Picking a vendor on price alone. Compare specifications and handover documents, not just the total. Our modular OT cost guide for India explains what actually drives price.
Get your OT layout reviewed before you build:
Already have a drawing, or still at the idea stage? Our team can review your layout against NABH requirements and give you a written specification you can use to compare any vendor.
Book a free OT layout review | Call +91 97164 12630 | WhatsApp us
