Operation theater Design Guidlines for HVAC

 

GUIDELINES FOR AIR CONDITIONING

IN OPERATION THEATERS

 

Air Conditioning in OT

 

A.        The air conditioning requirements for Operation Theater in a HCO have been deliberated at length with manufacturers, engineers, technical committee members and other stake holders and the following guidelines have been finalized.

 

B.        For this purpose operation theaters have been divided into groups:

 

1.         Super specialty OT: Super specialty OT means operation theatres for Neurosciences, Orthopedics (Joint Replacement), Cardio thoracic and Transplant Surgery (Renal, Liver etc.).

 

2.         General OT: This includes operation theatres for Ophthalmology, District hospital OTs, FRU OT and all other basic surgical disciplines.

 

Day care centre: Day surgery is the admission of selected patients to hospital for a planned surgical procedure, returning home on the same day, would fall under the category of general OT.

 

C.        The following basic assumptions have been kept in view:

 

·                Occupancy: Standard occupancy of 5-8 persons at any given point of time inside the OT is considered.

·                Equipment Load: Standard equipment load of 5-7 kW and lighting load of 1 kW to be considered per OT. For super speciality OT the equipment load can be taken as 7 – 9KW.

·                Ambient temperature & humidity at each location to be considered while designing the system.

 

REQUIREMENTS – Super Specialty OT

 

1.         Air Changes Per Hour:

 

·         Minimum total air changes should be 20 based on international guidelines although the same will vary with biological load and the location.

·         The fresh air component of the air change is required to be minimum 4 air changes out of total minimum 20 air changes.

·         100 % outdoor ventilation air systems are not mandatory. If HCO chooses to have 100% fresh air system than appropriate energy saving devices like heat recovery wheel, run around pipes etc. should be installed.

·         The supply & return air ducts must be of non-corrosive material.

·         No internal insulation or acoustic lining must be done on ducts as they can become breeding grounds.

 

 

2.         Air Velocity: The vertical down flow of air coming out of the diffusers should be able to carry bacteria carrying particle load away from the operating table. The airflow needs to be unidirectional and downwards on the OT table. The air face velocity of 25-35 FPM
(feet per minute) from non-aspirating unidirectional laminar flow diffuser/ceiling array is recommended.

 

Positive Pressure: There is a requirement to maintain positive pressure differential between OT and adjoining areas to prevent outside air entry into OT. Positive pressure will be maintained in OT at all times (operational & non-operational hours)

 

·         Laminar flow boxes/diffusers should be installed in the OT for supplying majority air and also majority return air should be picked up 75-150 mm above floor level.

 

3.         The minimum positive pressure recommended is 2.5 Pascal (0.01 inches of water)

 

4.         Outdoor Air intakes: The location of outdoor air intake for an AHU must not be located near potential contaminated sources like DG exhaust hoods, lab exhaust vents, vehicle parking area.

 

5.         Air handling in the OT including air Quality: Air is supplied through Terminal HEPA (High-efficiency particulate arrestance) filters in the ceiling .The HEPA can be at AHU level if it not feasible at terminal level inside OT. The minimum size of the filtration area should extend one feet (i.e. 304.8 millimetres) on each side of the OT table to cover the entire OT table and surgical team. The minimum supply air volume to the OT (in cubic feet per minutes CFM) should be compliant with the desired minimum air change.

 

6.         Air Filtration: The AHU (i.e. air handling unit) must be an air purification unit and air filtration unit. There must be two sets of washable flange type filters of efficiency 90% down to 10 microns and 99% down to 5 microns with aluminium/ SS 304 frame within the AHU. The necessary service panels to be provided for servicing the filters, motors & blowers. HEPA filters of efficiency 99.97% down to 0.3 microns or higher efficiency are to be provided .

 

7.         Temp & RH for Super-specialty OT:  It should be maintained 21 C +/- 3 C (except for Ortho for Joints replacement as 18 C +/-2 C) with corresponding relative humidity between 20 to 60% though the ideal RH is considered to be 55%. Appropriate devices to monitor and display these conditions inside the OT may be installed.

 

REQUIREMENTS – General OT

 

1.         Air Change Per Hour:

·                Minimum total air changes should be 20 based on international guidelines although the same will vary with biological load and the location.

·                The fresh air component of the air change is required to be minimum 4 air changes out of total minimum 20 air changes.

 

2.         Air Velocity: should be same as per previous guide.

 

3.         Positive Pressure: There is a requirement to maintain positive pressure differential between OT and adjoining areas to prevent outside air entry into OT. The minimum positive pressure recommended is 2.5   Pascal (0.01 inches of water).

 

4.         Air handling/Filtration: It should be same as previous.   When not possible, the OT's should be well ventilated with 2 levels of filtration with efficiencies as specified previously (pre and micro vee filters should be in position at the AHU).

 

5.         Temperature and Humidity: The temperature should be maintained at 21C +/- 3 Deg C inside the OT all the time with corresponding relative humidity between 20 to 60%.  Appropriate devices to monitor and display these conditions inside the OT may be installed.

 

 

 

 

Design considerations for Planning New Operation Theatres

 

OT Construction:

 

a)    The AHU of each OT should be dedicated one and should not be linked to air conditioning of any other area for all OT constructed.

b)    Window & split A/c should not be used in any type of OT because they are pure re circulating units and have convenient pockets for microbial growth which cannot be sealed.

c)         Paint- antibacterial, anti-fungal

d)         OT door – automatic/ Hermitically Sealed/Touch free (preferable)

e)         General Lights – Clean room lights

f)          Provision of safety against static charge.

g)         Separate power circuit for equipment like Laser.

h)         The anti-static flooring, walls and ceiling should be non-porous, smooth, seamless without corners (coving) and should be easily cleanable repeatedly. The material should be chosen accordingly. Anti-static Flooring – seamless, including  skirting, should not be of porous stone as it absorbs moisture and could be a source of bio-burden.

 

Maintenance of the system

·                During the non-functional hours AHU blower will be operational round the clock (may be without temperature control). Variable frequency devices (VFD) may be used to conserve energy. Air changes can be reduced to 25% during non-operating hours thru VFD provided positive pressure relationship is not disturbed during such period.

·                Validation of system` to be done as per ISO 14664 standards and should include:

ü   Temperature and Humidity check

ü   Air particulate count

ü   Air Change Rate Calculation

ü    Air velocity at outlet of terminal filtration unit /filters

ü    Pressure Differential levels of the OT wrto  ambient / adjoining areas

ü   Validation of HEPA Filters by appropriate tests like DOP (Dispersed Oil Particulate) /POA (Poly Alpha Olefin) etc.; repeat after 6 month in case HEPA found healthy.

·                Preventive Maintenance of the system: It is recommended that periodic preventive maintenance be carried out in terms of cleaning of pre filters, micro vee at the interval of 15 days. Preventive maintenance of all the parts of AHU is carried out as per manufacturer recommendations.

 

 

References

1.    American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) Standards. Ventilation for Indoor Air Quality. 2013

2.    FGI 2014

3.    CDC 2003 and 2005