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HVAC Fumigation design in pharmaceutical facilities
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HVAC Fumigation design in pharmaceutical facilities

1. Introduction


Proper design and implementation of fumigation systems are essential to meet regulatory requirements and maintain product integrity. In this blog post, we’ll explore the key considerations involved in designing HVAC fumigation systems for pharmaceutical facilities.

Cleanroom disinfection is a process required by Annex 1 of GMP, as stated in the following section:

4.33 The disinfection of cleanrooms is particularly important. They should be cleaned and disinfected thoroughly in accordance with a written programme. For disinfection to be effective, prior cleaning to remove surface contamination should be performed. Cleaning programmes should effectively remove disinfectant residues. More than one type of disinfecting agent should be employed to ensure that where they have different modes of action, their combined usage is effective against bacteria and fungi. Disinfection should include the periodic use of a sporicidal agent. Monitoring should be undertaken regularly in order to assess the effectiveness of the disinfection programme and to detect changes in types of microbial flora (e.g. organisms resistant to the disinfection regime currently in use).

Fumigation of cleanrooms is a common, almost systematic, process in those rooms with A or B classification (ISO 5 and ISO 7), PAL/MAL associated with these. It is also commonly used in bio-pharmaceutical facilities where pathogens are handled. However, it is not uncommon to find this process in lower classified areas, within sterile manufacturing environments.

The fumigation process consists of depositing a disinfectant on all surfaces of the room to be treated (ceilings, walls, corners, air diffusers, etc.) in a way that increases the effectiveness of surface cleaning up to 99.999%. As molecular micro-diffusion produces particles between 0.5 and 2 microns capable of penetrating all spaces.

A dry fog system is used for dispersion, which is responsible for dispersing the disinfectant liquid in the room to be disinfected. This disinfectant is placed in the nebulizer equipment, being a known and validated amount. Then it is dispersed into the environment, reaching all surfaces. It can have one or several atomizers, depending on the size of the room to be disinfected.

Other disinfection methods, that use vapour hydrogen peroxide, deserve specific considerations and we will discuss this in other posts.

2. HVAC Fumigation design in pharmaceutical facilities


When using this type of disinfection, the HVAC system and all its associated control systems must take into account the following:


  • The rooms to be fumigated must be clean. Remember: fumigation by itself is not a cleaning method.


  • The temperature and humidity of the rooms must be within a specific range to proceed with fumigation.


  • When fumigation is carried out, the ventilation system must be turned off to allow the dry fog system to release the disinfection product.


  • When the dry fog system finishes, the HVAC system must proceed to ventilate the room to remove the disinfectant product from the environment, introducing fresh air and sending it outside. If our HVAC system is through recirculation, we must install an additional fan to send this air outside. Likewise, if the supply of fresh air is very limited, we must provide a parallel air supply. All of this is through the appropriate motorized dampers.


  • The control system can be local or managed by the BMS, with the latter being preferable and more common. It is good practice to communicate the HVAC management system with the different elements involved: the nebulizer itself, HMI, particle counters (if they exist), fire detection system, interlocking door management system, and other signalling and warning elements. We will see this in a little more detail later.

3. A typical HVAC fumigation sketch


A fumigation sketch could be as follows:

Other options may be perfectly valid. For example, there may be two extractors, one for ventilation and one for recirculation, each with its corresponding dampers. This is particularly useful if the ventilation and recirculation flow rates are very different and/or if there are filters in the exhaust.

In any case, this system should be able to operate in normal mode and ventilation mode.

The normal mode, as the name suggests, is set to provide the necessary airflow and pressure to maintain the room classification. It should also provide fresh air to ensure the room is at positive pressure.

The ventilation mode should allow for the extraction of disinfectant-containing air from the room.

4. Operation sequence


Let’s take a look at an example of the operating sequence phases. In this example, we will assume that the control system is integrated into the BMS (Building Management System). Remember that you can use the Risk Analysis to determine the scope of the controls system.


4.1. Preparation


At this time, the HVAC system is operating in normal mode, where outside air is treated through the make-up unit (1) to maintain the required pressure differential in the room. Damper (2) is open. The extraction fan (3) is running, dampers (4) and (5) are closed, and (6) is open.

Before starting anything, the proper cleanliness of the room must be checked. Once this is done, the operator will introduce the dry fog system, following the filling procedure with the disinfectant to be used, quantities, time, etc. Then, the operator will leave the room and activate the signal in the BMS indicating that the system is ready to begin. It is common that the BMS is linked to the door interlocking system. In this case, it will give the order to lock the doors to prevent access by people during the fumigation process. It is important to take precautions in this case, to provide an emergency unlocking system from the inside for safety. Likewise, a visual signal will be activated to indicate that the room undergoing fumigation is in progress.

An important aspect to consider is the disabling of fire detectors, as they may trigger alarms.


4.2. Fumigation phase


In this phase, the HVAC system, make-up unit, and recirculation unit are stopped, and all dampers and the extraction/recirculation fan (3) are closed. The use of air-tight dampers is necessary for this type of application.

This phase is completely controlled by the dry fog system, which will release the disinfectant in the room during the programmed time. This system can be manual, and in this case, the BMS will only control the programmed time, or it can be connected to the BMS, indicating all phases of the process.

Below are two examples of dry fog fumigation systems from two different manufacturers:

4.3. Aeration phase


In this phase, the make-up unit (1) remains stopped, and dampers (2) and (6) remain closed. Then, dampers (4) and (5) are opened. Once the confirmation of the opening is received, the recirculation unit fan and the extractor (3) are started. It will remain in this state until the programmed aeration time is completed. This time has been studied and verified during the commissioning and qualification phases.


4.4 End of Cycle

Whether by time or by communication with the dry fog system, which sends a signal indicating the end of the cycle, the HVAC system must return to normal operation, with dampers (4) and (5) closed and (2) and (6) opened. Once they are opened, the make-up and recirculation units start. The extractor (3) adjusts its flow rate to normal operating conditions.

Once the normal room pressure difference is reached, the cycle can be considered complete, releasing any locked doors and changing the visual signal.

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