Indoor air quality is of paramount importance for human comfort and health. Air, whether it is from outside or re-circulated within the area, acts as a vehicle for airborne contaminants brought in by the movement of people, material, etc. Since many of these airborne contaminants are harmful either to products or people working in such environments their removal is necessary on medical, legal, social or financial grounds.

Cleanrooms are specially constructed, environmentally controlled enclosed spaces where the concentration of airborne particles (contaminants) is kept within specified limits. In industry, cleanrooms are used in the manufacturing of electronic hardware such as integrated circuits (ICs) and hard drives. In biotechnology and medicine, cleanrooms are used when it is necessary to ensure an environment free of bacteria, viruses, or other pathogens.

Four fundamental rules apply to cleanrooms.

• First, contaminants must not be introduced into the controlled environment from the outside.
• Second, the apparatus or equipment within the controlled environment must not generate or otherwise give rise to contaminants (for example as a result of friction,chemical reactions, or biological processes).
• Third, contaminants must not be allowed to accumulate in the controlled environment.
• Fourth, existing contaminants must be eliminated to the greatest extent possible, and as rapidly as possible.

These requirements are defined in Federal industry standard 209 and ISO 14644-1. Ittakes an incredible amount of technology to achieve and maintain these objectives. The HVAC system for cleanrooms is a specialized field requiring thorough understanding of cleanliness guidelines, airflow streams, room pressurization, temperature, humidity and filtration requirements, knowledge of codes and standards, specialty equipment,instrumentation and control, and many more details. This course will describe some basic requirements of HVAC design for cleanroom applications.

Airborne particles Characteristics

Airborne particles are solids suspended in the air. For our purposes, particles are defined as bodies with:

• Definite physical boundaries in all directions.
• Diameters ranging from 0.001 micron to 100 microns*
• Liquid or solid phase material characteristics.

*The size of contaminants and particles are usually described in microns; one micron is one-millionth of a meter. In English units one micron equals 1/25,400 inch. To give a perspective, a human hair is about 75-100 microns in diameter. A particle of 0.5 micron (200 times smaller than the human hair) can cause major disaster in a cleanroom.

Sources of Contamination

The airborne contamination level of a cleanroom is largely dependent on the particle generating activities in the room, besides the personnel who also contribute to the contamination levels. It has been found that many of these contaminants are generated from five basic sources (1) the facilities, (2) people, (3) tools, (4) fluids and (5) the product being manufactured. Review the list below to gain a better understanding of where the contamination originates.