CLASSIFICATION OF CLEAN ROOMS

The classification of cleanrooms can vary depending on the standard, country and terms used in its definition. If we look at the Spanish reference standard, the already advanced UNE 14644, a classification of rooms is established according to the level of demand in terms of the size and number of maximum particles present in the design area. In this way, and according to the first section (ISO 14644-1), 9 categories are established, from ISO Class 1 to ISO Class 9, the first being the most restrictive. By way of example, ISO Class 1 allows up to two particles of 0.2 micrometres or less per cubic metre of air, while ISO Class 9 allows up to 293 000 particles in that volume of air.

As stated above, classification by ISO standards is not the only existing standard. In the pharmaceutical industry, for example, it is mandatory to comply with the guidelines of the advanced GMP standards in the opening section. These standards classify rooms from the most restrictive class A (equivalent to an ISO Class 4) to D (equivalent to an ISO Class 8).

There is also a tendency in the industry to "talk" about classification under the American standard FED STD 209E. Although this standard was officially

this standard was officially withdrawn by the US Administration in 2001, its nomenclature and classification is still widely used.

For clarification purposes, the equivalence between the above-mentioned standards for the pharmaceutical industry together with the recommended design constraints is given below: 

CONSTRAINTS AND RECOMMENDATIONS FOR CLEAN ROOM DESIGN

As can be seen in the table above, there are critical design constraints and others that are not so clearly critical in the design and others that are not so clearly formulated in the aforementioned standards. Let us reflect on them:

• Temperature and humidity: The chosen point and the limits can be very specific and can be very specific and variable depending on the process to be process to be carried out in the cleanroom. It is necessary to Each case needs to be studied in depth, as there are no normative guidelines for some processes. A typical range for humidity is 30 to 65 % and 20-24 ºC for temperature. 

• Flow variability in non-operating bands For reasons of maintaining aseptic conditions and minimising contamination in the room, as well as to conserve energy in the working energy conservation in the working area, a minimum recirculation in non-operating bands is necessary. Although this can can be highly variable depending on the process, it is usual to keep it not to go below 25 to 50 % of the nominal flow rate.

  The standard determines the type of flow, laminar or turbulent, depending on the intended classification. It is also worth reflecting on this condition based on the selected system because it is a key factor in determining the required result.

• Filtration levels: Although specific standards should be used for the selection of the filtration specific standards should be used for the selection of the filtration system it is advisable to highlight some points indicated in the UNE 14644 as a recommendation:

   o  A pre-filtration of the outside air is recommended in order to quality in the air treatment unit is recommended. air treatment unit. In line with RITE, a combination of G4 with F7 filters can be used in the air handling unit. 

  o  A second filtering is recommended in the air handling unit to protect the filters. unit is recommended to protect the terminal filters. An F9 is usually the norm. 

  o  Terminal filtering. Very dependent on the category of the filter category depending on the process and classification to be obtained.  In some cases HEPA filtration must give way to ULPA filtration.

   

• Temperature monitoring:  The required temperature monitoring must be control must be indicated, as stated in standard UNE 14644 in order to take it into account not only in the process itself, but also depending on the equipment and materials of the the room, but also for the stability of conditions for the clothing of the for the clothing of the users of the room personnel to allow for the specified cleaning class. At this point, the following must be taken into account the following has to be taken into account here:

   o Lighting loads are high but stable over time. 

  o Process loads are usually highly variable and generally high. 

  o Occupancy loads are variable and can be high depending on the process.

In rooms with turbulent or multidirectional flow, the following guidelines are recommended:

o Design the conventional air distribution system by ceiling (zenithal).

o It is advisable to use a swirl type diffuser with high induction. The surface area covered by diffusers should be between 10 and 50% depending on the target class, aiming at an isothermal room air movement.

o It is advisable to return through vertical planes from the lower area or through false floors.

In unidirectional flow cleanrooms (commonly called in the standard and laminar sector) the following guidelines are recommended:

o The air must enter uniformly from almost all of one surface of the control volume.

o It must flow at a constant velocity and pass through the opposite surface on return.

IMPLICATIONS FOR THE DESIGN AND CONFIGURATION OF THE AIR HANDLING UNIT

Based on the above, a number of implications arise for the design and configuration of the air handling units to be selected:  

• To stabilise the humidity and temperature control loop, two main air handling units are desirable

o A larger one designed for recirculation of the air marked in the standard. It should be remembered that below ISO 5 more than 60 renewals per hour of the room to be classified are required. These values make it totally unfeasible to work with 100% outside air systems and therefore the process and filtering of the air flow required for recirculation of the room air must be controlled. The quality of the particulate level is given by the number of renewals and their high efficiency filtering, not the amount of outside air.

o A specific air handling unit for outdoor air treatment. The amount of outside air

is defined by the number of operators expected in the room and the required overpressure conditions in the area. If the process requires a specific humidity control (process humidity below 35 %), the selected drying system can be included in series, but bypassed.

• If the cleanroom has specific processes with high heat or humidity emission or adjacent spaces that require a certain pressure gradient to be maintained, it is necessary to include specific extraction units for this purpose