24 Aug Difference Between Absolute Humidity and Relative Humidity in Containment System.

Relative humidity and absolute humidity are two different concepts, although they both refer to the amount of water vapor in the air. Let us understand what exactly is Humidity and Relative Humidity.

Absolute humidity:

The whole mass of water vapor in a volume of air is what is referred to as absolute humidity. In other words, absolute humidity is the amount of moisture or water vapor present in the air. It is expressed as grams of water per letter of air (mass/volume). Absolute humidity (AH) is the ratio of the mass of water vapor to the volume of air.

If m is the mass of water vapor and V is the total volume, i.e. the volume of air and water vapor mixture, then Absolute Humidity AH is given by 

AH = m/V

Absolute humidity does not take temperature into account, but it does change with temperature and pressure. Absolute humidity is expressed in grams per square cubic meter gm/m3.

Relative Humidity:

Relative Humidity is the ratio of the partial pressure of water vapor in a volume of air to the saturated vapor pressure of water in the same volume of air at a given temperature. In other words, it is the percentage of moisture in the air compared to the maximum possible level of moisture in the air at the specified temperature. Because cold air holds more water vapors than warm air, relative humidity is higher at lower temperatures. A hygrometer (A hygrometer is a device that measures the amount of water vapor in the air, soil, or confined spaces.) is used to measure relative humidity, which is also known as %RH.

Role of Absolute and Relative Humidity in an Isolator:

Before proceeding to the Condition Phase and the injection of vaporized hydrogen peroxide, the Dehumidification Phase of the VHP Generator must satisfy two independent variables: 

• Programmed time
• Absolute humidity

In the case of a VHP Generator, absolute humidity is measured in the air stream returning from the isolator within the VHP Generator. After the Dehumidification Phase has finished, the control system checks to see if the absolute humidity parameter has been satisfied.

If the absolute humidity is greater than or equal to the programmed absolute humidity, the control system dehumidifies until the absolute humidity parameter is met. If the temperature in the VHP Generator return is higher than normal, it will take the VHP Generator longer to satisfy the absolute humidity parameter. This is because as the temperature rises, so does the amount of dehumidification required to achieve the absolute humidity parameter.

Wrapping up:

The distinction between humidity and relative humidity has long been a source of consternation. Relative humidity is an important factor that influences the quality of pharmaceutical products. Controlling humidity is critical in processes such as granulation and compression.