Sash Arrangements

The position of the Clean Air fume hood sash is crucial for safety and effectiveness in a laboratory setting.

Sash as a Safety Barrier: The sash, essentially the front window of a fume cupboard, is typically made of 6mm toughened glass. It slides open and closed, usually vertically, to access the internal chamber. This barrier is essential for containing hazardous gases, fumes, and aerosols generated within the chamber and protecting the operator. When closed, it also shields the experiments from external air flows and turbulence while allowing light into the chamber.

Operation Mechanism: The sash operates smoothly on a weighted counterbalance system. Its movement can be adjusted for ease of use by turning spring-loaded adjustment screws in the sash guide track.

Varieties of Sash Arrangements:

• Plain Vertical Sliding Sash: Commonly used by Clean Air, this sash slides upwards for chamber access.
• Plain Horizontal Sash: Sliding sideways, these are more common in robotics and ventilated enclosures but less so in fume cupboards.
• Combination Sash: These feature horizontal sliding panes within a vertical rising frame, offering straightforward and safe access.
• Bespoke Sash Arrangements: Clean Air can design custom solutions for unique requirements, such as double sash systems. These are especially useful in specific applications like life sciences R&D.

Walk-In Fume Cupboards: These larger units may have vertical sliding or combination sashes. A linked pulley system ensures smooth and synchronised opening in taller cupboards with multiple sashes.

Sash Materials:

• Toughened Glass Sash: Standard sashes are made of strong, safety-toughened glass. If broken, they shatter into blunt pieces rather than sharp shards.
• Polycarbonate Plastic Sash: Recommended for use with hydrofluoric acid (HF), as HF fumes can etch glass. Polycarbonate resists corrosion and withstands acid fumes.

The Sash Stop: Most fume cupboards have a sash stop to maintain the sash at a safe working height during experiments. This stop can be overridden for loading/unloading but should be returned to the safe level after these activities. The positioning of the sash stop is determined based on the fume cupboard’s dimensions and the desired face velocity at the working aperture. Lowering the sash improves the clearing rate of the fume cupboard.

The different sash arrangements for fume cupboards cater to various laboratory needs and safety requirements. Here are the primary types:

1. Plain Vertical Sliding Sash: This is the most common type of sash arrangement provided by companies like Clean Air. In this design, the sash slides vertically upwards to allow access to the internal chamber of the fume cupboard.
2. Plain Horizontal Sash: The sash slides horizontally along a track in this arrangement. This type of sash is often used in robotics and ventilated enclosures but is less common in standard fume cupboards.
3. Combination Sash: This design features horizontal sliding panes within a vertical rising frame. The combination sash system offers easy and safe access for the operator.
4. Bespoke Sash Arrangements: Bespoke sash arrangements can be designed for specific needs. For instance, Clean Air’s design team can create double sash systems for certain applications, like life sciences research and development.
5. Sashes for Walk-In Fume Cupboards: Larger walk-in fume cupboards may feature vertical sliding sashes, combination sashes, or other customised arrangements. In taller units with multiple sashes, a linked pulley system can be used for smooth and simultaneous operation of the sashes.

The Sash in a fume cupboard is critical in ensuring the operator’s safety. Here’s how;
1. Containment of Hazardous Substances: The primary function of a fume cupboard is to contain and exhaust hazardous fumes, vapours, and particulate matter. When closed or in the lowered position, the Sash acts as a physical barrier between the operator and the hazardous substances inside the fume cupboard, ensuring that these harmful agents do not escape into the laboratory environment.
2. Protection from Spills and Splashes: In the event of a chemical spill or splash inside the fume cupboard, the Sash helps protect the operator from direct contact with the chemicals, reducing the risk of chemical burns or injuries.
3. Protection from Fires and Explosions: In the event of a fire or minor explosion within the fume cupboard, the Sash can help contain the flames and minimise the spread of fire, protecting the operator from potential harm.
4. Shielding from Flying Debris: If a reaction becomes volatile or an apparatus breaks, the Sash can protect the operator from flying debris or shattered glass.
5. Regulation of Airflow: The Sash’s position can affect the airflow and face velocity of the fume cupboard. A properly positioned sash ensures that the fume cupboard maintains the right face velocity, crucial for efficiently removing hazardous substances and preventing their escape into the lab environment.
6. Visibility and Lighting: The transparent nature of most sashes (often made from toughened glass or polycarbonate) allows operators to see their experiments. This transparency, combined with the lighting in many fume cupboards, ensures that operators can safely and effectively observe and manipulate their work without needing to open the Sash frequently.
7. Emergency Shutdown: Some advanced fume cupboards have sensors that detect when the Sash is left open for extended periods. If the Sash remains open beyond a set time, these systems can trigger alarms or even close the sash to ensure safety.
8. Energy Efficiency and Cost Savings: While not directly a safety feature, the ability to lower the Sash can lead to energy savings if VAV controls are fitted. Lowering the Sash reduces the volume of air that needs to be exhausted, which can lead to energy savings and reduced costs. Labs can promote safety and efficiency by educating operators on the importance of lowering the Sash when not occupying the fume cupboard.

Multiple sash arrangements are available for fume cupboards because different applications and laboratory setups have varying requirements. Safety, usability, specific experiments, and ergonomic considerations can influence the choice of sash arrangement. 
 
Why Multiple Sash Arrangements Exist;
1. User Requirements: Different laboratory processes or experiments might require unique fume cupboard access patterns. For instance, some processes may require broad horizontal access, while others may need more vertical space.
2. Safety: Certain sash designs offer better containment or protection depending on the chemicals and procedures used.
3. Space Constraints: In some laboratory setups, there might be limited space in front or at the sides of the fume cupboard. This could influence whether a vertical or horizontal sliding sash is more appropriate.
4. Ergonomics: For ease of use, the type of Sash can be selected based on the height of the users, the tasks they are performing, and the equipment they are using.
5. Aesthetics and Visibility: Some sash designs, like those with a larger glass area, provide better visibility and might be preferred in teaching labs or demonstrations.
6. Specialised Applications: Certain applications, like robotics enclosures, might have specific sash requirements that standard designs can’t fulfil.

1. Evaluate the Application: Determine the primary purpose of the fume cupboard. For instance, for a specific procedure or to handle certain equipment, the Sash should accommodate easy access for those needs.
2. Consider Safety: If you work with particularly volatile or hazardous substances, you might prioritise sash designs with the best containment and protection.
3. Assess Space and Layout: Measure the available space and consider how users move around the fume cupboard. A horizontal sash might be more appropriate if there’s limited space in front of the fume cupboard.
4. User Comfort: Think about the height and reach of the primary users. A combination sash might be beneficial if users vary significantly in height, ensuring everyone can access the fume cupboard comfortably.
5. Maintenance and Durability: Some sash designs might be easier to maintain, clean, or repair. Additionally, consider the durability of the sash material, especially if it will beexposed to corrosive chemicals.
6. Cost: While safety and usability should never be compromised, budget constraints might influence the choice of sash arrangement.
7. Consult with Manufacturers: Discuss your specific needs with fume cupboard manufacturers. They can provide insights into the best sash arrangement for your laboratory and offer custom solutions if necessary.