What are HEPA filters?

HEPA filters are one of the most reliable and dependent filters used in the pharmaceutical industry. They help mitigate problems related to contamination in the air to increases the efficacy ,quality and safety of the pharma process

What is a HEPA filter?

HEPA stands for High-Efficiency Particulate Air and is a mechanical filter designed to filter out much of particles, typically up to 99.7%. These includes pollen, dust, mold, bacteria, and common airborne particles of the size of 0.3 microns (µm). 

They are the main components of filtration in a given pharma process and equipment, widely used in all critical pharma processes, specifically that required high degree of purity. 

To use HEPA filters in any system and if large sized particles are present in the air, initially large-sized particulate filters are placed to remove large sized particles. When the air only contains small sized particles. After that, the air is exposed to the HEPA filter, to eliminate the remaining small particulates. This configuration increases the life and efficiency of the HEPA filters because directly exposing the HEPA filter to large particles will affect the physical structure of the HEPA filtering media.

In the pharmaceutical industry, HEPA filters air in critical areas, such as injectable filling and clean rooms. 

Construction and Working

HEPA filters are mechanical filters made up of randomly arranged fibers of materials such as polypropylene, polyester, or fiberglass in a pleated form. The pleated structure creates a narrow pathway for the air to pass and traps oversized particles. 

The HEPA filter’s working can be divided into any of the three mechanisms: diffusion, interception, and impaction.

Diffusion - This phenomenon occurs for the particles below 0.3µm, when the particles collide with gas molecules. The collision delays the passages of smaller-sized particles from the filter media, and ultimately collides with the filtering material.  The delay and collision increase the probability of the other techniques (interception and impaction) to come into action and stop the particles.

Interception occurs when the particle flowing in the air comes in contact with the filtering material (fiber) and is captured to prevent flowing across the filter. The effectiveness of this phenomenon depends on the filtering material sizing, which increases when the material size is close to the size of the particle.

This phenomenon is effective for mid-sized particles.

Impaction - This phenomenon occurs for large-sized particles because they cannot avoid the material's fiber and end up being caught up by the HEPA filter.

Design considerations

Design considerations for HEPA filters are their attributes, which impacts their effectiveness in air filtering. They can include the following:

Air flow rate

It is the rate of air flowing across the filtering media in a given unit of time. It is critical because HEPA filters consist of dense material that can obstruct airflow. The selected HEPA filter must provide a specified airflow tailored to a specific process or application, which must be considered during equipment or process design. This is important because some pharma process or equipment requires specific airflow for their process to occur. Installing HEPA filter reduces the existing airflow, which is consider when designing a process, and it depends on the design of HEPA.  If the airflow of HEPA filter fluctuates from the its design flow, it will also affects the process airflow, which is not good

Additionally, as the filter becomes clogged with particles, the air pressure reduces, and the resultant airflow is less than the design flow. The HEPA filters must be regularly maintained and replaced if required to prevent this condition.

Particulate Size

Particulate size is the parameter that defines the ability of a HEPA filter to filter out the flowing air through it. Indicated in the percentage, it represents a specific particle size.

The particle size can be 0.1µm, 0.2µm, and 0.3µm, and the efficiency can be 99.97& 95%. Higher efficiencies and smaller particle sizes can also be achieved depending on the HEPA filter material design.

Applications of HEPA filters

The pharmaceutical industry is one of many industries where the HEPA filter application has been widely accepted and implemented. 

Let's discuss some of the many.

Clean Room

A clean room is a specially designed room for pharma applications, where the inside environment, i.e., temperature, humidity, airflow, and contaminants, are controlled to cater to the critical pharma product or process. HEPA is used to capture particulates and filter the incoming air to provide contamination-free air.

The HEPA filters are installed above the clean room ceiling in the way air flows. The blower motor generates the airflow that flows through the HEPA filter. As air flows through it, the particles are filtered out, and the resultant air flowing into the clean room is cleaned up to the efficiency of the HEPA filter.

The selection of HEPA filters for clean room application depends on the clean room class; the higher the class, the higher the efficiency required. 

Isolators

Isolators provide isolation between working humans and the pharma process being carried out. Sufficient accessories and tools are provided to execute the process while in complete isolation. An essential part of isolator is filtration, and depending on the equipment, process, and requirement, HEPA filters are also used.

The HEPA filter is installed at the exhaust, where toxic and dangerous gasses and fumes are exhausted. The HEPA captures these toxic gasses to prevent environmental damage and protect organizations from ecological and compliance issues.

AHU Systems

Air Handling Unit – AHU is a dedicated equipment that provides conditioned air (hot or cool) into the required area. One application of AHU is to provide particle- and contaminate-free air according to the area and process requirement. 

The final filtration stage is the HEPA filter. Other large-sized filters, such as bag filters, remove large particles, before being exposed to the HEPA filter. The main reason for following this sequence is that if large-sized filters are not used and the air is directly exposed to the HEPA filter, large particles will damage the physical structure, making the HEPA filter in-efficient and useless.

The HEPA filter is installed in the supply section of the Air Handling Unit, where air finally flows through the HEPA filter before flowing into the area. The HEPA filter characteristics depend on the process or area to which the air is supplied.

High-temperature HEPA filtration

Another application of HEPA filters in the pharma industry is in high-temperature equipment applications such as Dry Heat Sterilization - DHS. This equipment sterilizes items inside by flowing high-temperature air. Since items inside often come from pharma products, the air must be free from foreign particles and contaminants. This is achieved by using HEPA to filter the incoming air.

The HEPA type used in this equipment is called High temperature or Heat restrain HEPA filters. They can sustain high temperatures (for example, up to 250° C) without damaging the filter's physical structure. They are comprised of a stainless-steel structure. Glass fiber is used as a filtering material that can sustain high temperatures. 

Advantages of HEPA Filters

Let's see how HEPA filters are helping the pharmaceutical industry in achieving their productivity.

• HEPA filters can remove 99.97% of airborne particles, thus providing near-ideal air purity in manufacturing areas. This can help increase product safety and quality, especially in injectables and biotech products.

• Using HEPA filters helps in efficiently achieving regulatory compliance because of its high recognition and acceptability for pharmaceutical applications.

What is HEPA filter testing, and why is it required

As with other pharma equipment, accessories, and tools, HEPA filters also have a definite lifespan, after which they must be replaced. However, deciding when to replace HEPA filters is very important because there is not a specified time. Rather, it depends on the application, frequency, and particle characteristics to decide for HEPA replacement. 

A more practical and realistic approach is to conduct tests to check for its effectiveness in filtering out the contaminants.  

DOP testing is the most common test performed to check the efficiency of HEPA filter filters. Its objective is to check whether the filter is effectively removing the particles for which it is meant for 

The DOP Test

In this test, an aerosol involving the oil particulates is released upstream of the filter. After the downstream, these particulates are measured with a photometer to calculate whether these oil particulates have leaked through the filter by checking traces on the filter's surface for pinhole leaks. 

Through this test, we can measure the HEPA filter integrity and see if there are any leaks in the filter frame and seals. 

How often does the HEPA filter be tested?

Deciding when to test the HEPA filter is critical and careful selection enhances its performance. Some instances where performing HEPA filters is essential include the following.

• When a HEPA filter is initially installed, the test can verify its      effectiveness and integrity.

• When there is significant mechanical maintenance involving HEPA filters, for      example, repairing or altering the frame design of HEPA

• Checking the effectiveness of the older filter before replacement. Similarly,      replacing a new filter and checking ensures its effectiveness.

• At set frequency, i.e., half-yearly or yearly. It is best to follow the manufacturer's recommendation or quality department guidelines. Regulatory guidelines can also be used to set its testing frequency.