Where critical deviations are born (or avoided)
In the previous article of this series of three technical publications We address how modern pharmaceutical design should be based on risk analysis and the principles of Quality by Design (QbD). In this second installment we descend to the terrain where these principles materialize in a more visible (and more critical) way: the Plant architecture, operational flows and HVAC systems.
Experience shows that a high percentage of deviations, root cause investigations and regulatory observations do not originate in the process itself, but in layout and environmental control decisions made in early design phases. Correcting them once the plant is in operation is usually complex, expensive and, in some cases, impossible without a profound redesign.
Flow logic as a guiding design principle
Pharmaceutical architecture is governed by a fundamental concept: flow logic. The objective is not only operational efficiency, but also systematic prevention of cross contamination and confusion errors.
Every design must demonstrate clear and consistent control of:
- Personnel flows
- Material flows
- Waste streams
These flows must be unidirectional, segregated and understandable, both for operational personnel and for a regulatory inspector.
A correct layout is one that “explains by itself” how risk is controlled.
Personnel flows: the dominant risk factor
Personnel are the main source of particles and microbiological contamination in a clean room. Therefore, the design must integrate effective transition and control systems.
Personnel Airlocks (PAL – Personnel Airlocks)
Clothing locks are not residual spaces; are critical control zones. Your design must consider:
- Clear separation between street clothing and pharmaceutical clothing,
- Logical sequence of clothing,
- Easy to clean surfaces,
- Adequate pressure control.
Depending on the process, the locks can be designed as:
- “Bubble” type, with higher pressure than adjacent areas, to prevent the entry of contaminants.
- “Sink” type, with lower pressure, to contain contaminants in high-power or toxic processes.
Typical design error
Locks correctly classified but without a clear operational sequence, which generates recurring deviations due to incorrect use of personnel.
Material Flows: Protecting Air Integrity
Materials that access classified areas must do so through systems that preserve air quality and segregation of areas.
Material Airlocks (MAL – Material Airlocks)
Among the most common solutions are:
- Pass-through boxes, equipped with electromechanical interlocks that prevent the simultaneous opening of both doors.
- Sterile transfer systems, such as rapid transfer ports (RTP), especially in processes with isolators or RABS.
The design must consider not only the input of raw materials, but also intermediate materials, tools, cleaning materials and waste output.
Segregation of processes in multi-product facilities
In multi-product plants, the physical and functional segregation It is a key requirement to avoid cross contamination.
A robust design should allow deep cleaning of a room without affecting adjacent rooms, some independent drainage systems and correctly filtered and segregated air returns.
Segregation should not depend solely on procedures; must be incorporated into the architecture itself.
The HVAC system: the invisible heart of the plant
The HVAC system is the more complex critical service of a pharmaceutical facility. Its design must align with ISO 14644 (clean room classification) and GMP Annex 1 (sterile processes). A pharmaceutical HVAC is not limited to air conditioning; controls critical variables with mathematical precision.
Critical control parameters
Among the most relevant parameters are:
| Air changes per hour (ACH) | Typically between 20 and 40 for Grade B and C areas, ensuring effective particle sweeping. |
| Pressure differentials | Normally staggered in steps of 10–15 Pa between areas of different classification, ensuring air flow from cleaner to less clean areas. |
| Relative humidity (RH) | Critical for certain products (effervescent, hard gelatin capsules), usually controlled in ranges of 40–50% ± 5%. |
Absolute Filtration and Unidirectional Flow
The location and type of HEPA (High-Efficiency Particulate Air) filters are decisive.
In aseptic filling areas (Grade A) it is required laminar or unidirectional flow, a typical speed of 0,45 m/s ± 20 % and the product must remain under a “curtain” of sterile air at all times.
The design must demonstrate that the flow pattern protects the critical point of the process, not only that it meets a theoretical value.
Frequent regulatory observation
Correctly designed unidirectional flows but degraded by physical interferences (lighting, machine arms, operator movements).
HVAC, risk and operational sustainability
An oversized HVAC system not only increases OPEX; can become a operational risk if not flexible.
Modern engineering is committed to a variable flow system, controlled sleep modes and maintenance of differential pressures even during periods of inactivity. All this without compromising the classification of the areas or the safety of the product.
Conclusion: the layout and the air are also validated
Architecture and HVAC are not auxiliary disciplines: they are core elements of quality control. A coherent, defensible and risk-aligned design facilitates daily operation, validation and technical defense against inspections.
On the contrary, an error in this phase usually accompanies the installation throughout its useful life.
Accede a los artículos de la serie:
- Design of pharmaceutical facilities under the QbD paradigm
- Closing the cycle: From Risk Analysis (QbD) to Objective Evidence of operation
Are your layout and HVAC designed to operate… or just to comply?
Many facilities work, but few are actually prepared for a demanding inspection.
If you would like an independent technical review of your layout, flows or HVAC design from a GMP and risk management approach, we can help them.