Pass though boxes

Material transfer during the manufacturing operation is necessary, and care is taken not to disturb the area and environmental parameters. However, since humans are involved in material transfer, it often becomes challenging to maintain these parameters.

The pharma industry uses various process and equipment to enable humans transfer material without disturbing environmental conditions, and pass through is one of many.

What are Pass Throughs?

Pass-through boxes are mechanical enclosures that facilitate materials & Items transfer in and out of two areas without affecting the area inside. They prevent disturbance in the area parameters such as airflow and purity during material transfer.

The main reason for their usage in the pharma industry is because, during manufacturing, it is not recommended and allowed to use doors or regular entry points for transferring material in and out of the area. Instead, a dedicated opening and pass-through equipment are used to transfer them. They are designed and manufactured according to the equipment, items, and accessories to be moved.

The transferring area can be of the same class, purity level, or different. However, it is also case different class areas require material transfer

Pass through consist of two doors are two sides. They are installed at that side of the wall location where material transfer is required. One opening is on the critical side, while others are on the non-critical side. The doors at both openings cannot be opened simultaneously, thereby preventing exposure of the dirty side to the clean side. 

They are sealed at every point to prevent cross-leakage & contamination and provide separation between two areas. 

Another purpose of pass-through is to act as a barrier between critical and less necessary areas, effectively preventing damage to the crucial area's environmental parameters. 

Types of pass-throughs

 Two common types of pass-throughs are used in the pharmaceutical industry - static and dynamic. Let's discuss briefly each of these.

Static Pass-throughs

Static pass-throughs transfer items between areas of the same classification or purity level. Their design and construction are less complex, with no filters and interlocking, since they do not require strict control.

Dynamic Pass-throughs

Dynamic pass-throughs transfer items between different classification area, such as clean areas and corridor. They are built to prevent disturbance in the environmental parameters since the other side of the pass-through is of lower air quality. 

An important feature of dynamic pass-through is door interlocking, which helps prevent the opening of both side doors. The interlocking can be mechanical or automated.

• In mechanical interlock, the door is mechanically designed in a way that allows only one door to be opened.

• In automated interlocks, electromagnetic locks do not allow a door to be opened if the opposite side of the door is opened.  The door opening and closing are sensed using various sensors that can sense if a door is closed or open, and a corresponding lock is controlled through electronics means

• Door interlocking prevents accidentally opening both doors simultaneously, contaminating the clean side with less classified area.

The design and construction of dynamic pass-throughs are more complex than static pass-throughs. Some additional components present in the dynamic include, but are not limited to 

• Filters are installed at supply and suction to filter the air into the pass-throughs. Because, air is used to shower the material inside before the discharge side door is opened for off-loading,  to remove any impurities from them. HEPA filters can also be used depending on the process and area requirement.

• UV Light - UV light can also be added to disinfect the items inside before being transferred from one side to another

• Blower Fan - A small blower to blow filtered air into the chamber 

The dynamic pass-throughs are also equipped with a power supply unit to power the electronics in the pass-through.

Construction

As mentioned, a pass-through box is a mechanical structure of appropriate dimensions to fit on one side of a wall. Their dimensions are carefully selected to suit the physical area dimensions and the process requirement.

Enclosure - Pass-through is a rectangular or square-shaped mechanical structure made of pharma-grade material—the mechanical enclosure houses all necessary components, such as doors and internal components. The size of the enclosure depends on many design factors, such as application, available area, and items used in the process.

Material of construction. The construction material of pass-through boxes, including hinges, grills, and doors, comprises stainless steel 304. Because pass-through does not come in direct contact with the product, SS304 can be safely used. 

Doors - Each pass-through has two doors to facilitate movement between two areas, with appropriate support components such as handles and hinges. In static pass-through, the door is manually operated. While in, the dynamic pass-through door is interlocked with an appropriate electromagnetic or mechanical locking mechanism. In some pass-through models, the door is also provided with sensors to detect the open or closed state of the door.

Doors are also provided with glass windows to view inside the pass-through chamber.

Grills - grills are installed inside the pass-through chamber at the sides or upper portion. They facilitate filtered air entry and exit from the pass-through.

Air Supply System – A dynamic pass-through air supply system is installed to purify the items inside before opening the date and transferring items to another side. It consists of 

• An air blower is used to blow air inside the chamber. The motor is controlled through a centralized controller that takes input from the door sensor. When the controller senses the door close position, it runs the blower motor for a pre-set duration. The filtered air through different filters flows into the chamber. After time has elapsed, the blower motor stops and the door can be opened. 

• Filters to clean the air flowing into the chamber: some manufacturers also use HEPA filters, the selection of which depends on the area of application and process requirements.

Electrical & Electronics – as with other pharma equipment, pass-throughs are also provided with electrical & electronics control to operate the equipment. Some standard components include but are not limited to 

• UV light - some pass-throughs might include UV in their design for disinfecting purposes.

• Motor - to operate the blower as discussed earlier in this article

• Light indicators for doors - indicators for doors indicate whether the door is open or closed. Its purpose is to give a visual indication for operators, as the noise and process working can distract operators from pass-through working.

• Differential Pressure - it is used to indicate Pressure inside the chamber. Some pass-throughs could also include manual pressure gauges.

• Controller - it is used to control the operation of a pass-through, such as a door closing, opening, and blower start/stop

Application and advantages of pass-through in the Pharma industry

The main application of pass-through in the pharma industry is in clean rooms. They are used to 

• Transferring material, accessories, tools, and equipment into the area for processing during the production process

• Transferring material such as used media, product samples, used instruments, accessories & items from the clean room

Advantages

• The main advantage of pass-through is that they limit human movement inside and outside the critical area, significantly reducing the contamination in the area.

• Pass-through also enables transferring sensitive pharma products that are vulnerable to contamination by using the dynamic pass-through environmental control feature.

• Pass through remain clean and durable, proving a trusted option for pharma customers for their critical applications. Additionally, they can be custom-manufactured and designed for your pharma requirements.

Working principle 

Dynamic pass-through

• Items are placed into the dynamic pass-through, by opening the door, which is open by pressing the open button on that side. If the other side door is closed, the door can be opened. On the contrary, if the other side door is opened, the operator must wait until the other door is closed.

• The operator places items to be transferred inside the pass-through and closes the door.

• When the door is closed, the pass-through showers filtered air inside pass-through on the items for a pre-set period. The time setting can be done through the main panel, or it can also be fixed when designing and manufacturing the pass-through. The selection of which depends on the buyer's requirements

• After showering time has elapsed, the blower stops, and items are ready to be discharged. 

• The operator at other side opens the door and collects the items from pass through. 

• The exact process is repeated to transfer material from the other side. 

Static pass-through

The working principle of static pass-through is simple, as no complex parts or operation is required. 

• The operator places items to be transferred into the pass-through and closes the door. Since static pass-throughs are used in the same level of cleanliness, they are commonly not provided with door interlocking. If such is the case, the door can be opened, even if other side door is opened. 

• After placing items in the pass-through, the operator on the other side can open the door and take the items out.

• The exact process can be repeated when transferring items from the other side.

About the Author:

Muhammad Asim Niazi

Muhammad Asim Niazi has a vast experience of about 11 years in a Pharmaceutical company. During his tenure he worked in their different departments and had been part of many initiatives within the company. He now uses his experience and skill to write interested content for audiences at PharmaSources.com.