Cleanrooms are highly controlled environments that use scientific principles of physics, chemistry, biology and mathematics to minimize contamination and ensure air quality. From particulate filtration to ultraviolet light disinfection, every process in a cleanroom is based on sound science.
In this article, we explore just some of the key principles that enable these facilities to function properly, explaining their scientific basis and how they are applied in practice.
1. Air Filtration and Brownian Motion
Principle
Brownian motion is the random behavior of microscopic particles. suspended in a fluid. This phenomenon is crucial to understanding how filters HEPA capture ultrafine particles.
Scientific Basis
Brownian motion was observed by Robert Brown in 1827 and explained by Albert Einstein in 1905. It occurs when small particles are constantly hit by moving molecules, causing them to follow erratic trajectories.
Clean room application
HEPA (High-Efficiency Particulate Air) filters use this principle to trap particles smaller than 0.3 micrometers. Due to their erratic movement, these particles end up colliding with the filter fibers and are trapped, ensuring clean air in high-demand rooms, such as sterile drug production.
Laminar Flow: The Elegance of Unidirectionality
Principle
Laminar flow refers to a pattern of air movement in which air flows in parallel layers without mixing or turbulence.
Scientific Basis
This concept was described by Osborne Reynolds in the 19th century and is based on the difference between laminar and turbulent flow. In a laminar flow, air moves in an orderly manner, while in a turbulent flow, swirls and mixing of particles occur.
Clean room application
In ISO 5 environments, such as sterile filling areas, HEPA diffusers are used which generate a laminar flow with velocities of approximately 0.45 m/s. This type of flow allows particles to be carried out of the work area without recirculation, which is essential to ensure sterility.
3. Pressure Differentials: Controlling the Air Direction
Principle
Cleanrooms often use pressure differentials to generate air currents to prevent contaminants from reaching critical areas.
Scientific Basis
This principle is based on Bernoulli’s equation, which explains how changes in air pressure can induce movement. In a clean room, the pressure remains higher in the most critical areas, forcing air out into less clean areas rather than in.
Clean room application
For example, in an ISO 7 environment adjacent to an ISO 8, the air pressure in the cleaner room is kept approximately 10-15 Pascals higher to ensure that air flows in the correct direction, protecting sensitive products from outside contamination.
4. Triboelectric Effect: When Friction Charges the Environment
Principle
When walking, moving or handling certain materials, friction is generated. This friction causes an exchange of electrons, giving rise to electrostatic charges on surfaces.
Scientific Basis
This phenomenon, known as the triboelectric effect, was already observed by Thales of Miletus around 600 BC. The charges generated can attract particles in suspension or even discharge on sensitive equipment, compromising the integrity of delicate products.
Clean room application
In environments such as microelectronics, where electrostatic discharge is a critical risk, conductive soles, antistatic materials and ionizers are used to neutralize the charges generated by friction. This maintains a safe environment in the face of an invisible but very real enemy.
5. Biocontamination and Biodecontamination Methods
Principle
Bacteria, fungi and viruses can attach to airborne particles and spread in closed environments. Effective removal of microorganisms is critical in cleanrooms.
Scientific Basis
Airborne microorganisms range in size from 0.2 to 10 micrometers, which makes them susceptible to the same principles that govern particulate filtration but, in addition, they can be removed by chemical oxidation processes or exposure to UV radiation.
Clean room application
Ultraviolet Light (UV-C)
- UV-C radiation (wavelength of 254 nm) destroys the DNA of microorganisms, preventing their replication.
- It is used in air conditioning systems, disinfection of critical surfaces and containment and protection equipment such as SAS Pass-boxes.
Vaporized Hydrogen Peroxide (VH₂O₂)
- It is a chemical biocide that oxidizes cell membranes and genetic material of microorganisms.
- It is used in equipment such as Isolators and RABS as well as in terminal decontaminations of clean rooms through nebulization cycles that achieve a reduction of up to 6-log, eliminating 99.9999% of bacteria and viruses.
These methods complement HEPA filtration to ensure environments free of biological contamination.
6. Algorithms and Adaptive Control: Intelligence in Air Regulation
Principle
Mathematical algorithms make it possible to optimize the air renewal rate, adjusting flows according to demand in real time to improve energy efficiency without compromising air quality.
Scientific Basis
Adaptive control systems use mathematical models to monitor variables such as particle concentration, pressure and humidity, and adjust the HVAC system as needed.
Clean room application
Advanced systems employ controllers and algorithms to modify fan speed and renewal rate based on ambient particulate load. Reducing energy consumption by reducing ventilation when the room is not in use, without compromising cleanliness when higher air renewal is required.
Clean rooms are a demonstration of how the principles of physics, chemistry, biology and mathematics can be applied in an integrated manner to create controlled and highly efficient environments.
From particle capture by Brownian motion, to pressure regulation using Bernoulli’s equation, to the use of UV-C and VH₂O₂ to kill microorganisms, every aspect of their operation is backed by decades of scientific advances.
