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Sash Arrangements

The sash is the front window of a fume cupboard. Fume cupboards typically feature a 6mm toughened glass sash which slides open and closed vertically, allowing access to the internal chamber. However, there are multiple sash arrangements available with both vertical and horizontal operations.

The sash provides containment and protects the fume cupboard operator from any hazardous gases, fumes, aerosols, etc. given off by experiments and chemical reactions within the chamber. The closed sash also protects the experiment from external disturbance from air flows and turbulence. In addition, it allows light into the fume cupboard chamber.

The sash rises and lowers smoothly on a weighted counterbalance system. Generally, spring-loaded adjustment screws in the sash guide track can be turned in or out to vary the tension of the guide on the sash. This allows the sash to travel freely.

The Different Sash Arrangements

The radius profile frontal design of the APEX fume cupboard range provides a smooth curved entrance and the high-level glass panel gives full viewable access to the internal chamber. Both the APEX-2 and APEX-3 operate at low volume flow rates down to 0.3 m/s.

Plain Vertical Sliding Sash

The plain vertical sliding sash is the most common sash arrangement by Clean Air. It slides upwards, allowing access to the fume cupboard chambers.

Plain Horizontal Sash

Horizontal sashes slide sideways on a track. They are commonly used for robotics enclosures and ventilated enclosures, but rarely for fume cupboards.

Combination Sash

Combination sashes feature horizontal sliding panes in a vertical rising frame. This sash system offers simple and safe access to the operator.

Bespoke Sash Arrangements

Double Sash

The experienced Clean Air design team will also design bespoke sash arrangements to suit any application.

For example, these unique double-sash fume cupboards have been designed and built to meet our client’s exact specifications. The double sash arrangement is ideal for this client’s life sciences R&D.

Sashes for Walk-In Fume Cupboards

Walk-in fume cupboards can also have sliding vertical sashes and combination sashes. Because the walk-in units are taller, they will feature at least two sashes. If they have three or more, the Clean Air team will develop a linked pulley system to allow them to rise quickly and smoothly.

For example, with a three sash arrangement the middle sash will be designed to rise twice as fast as the top one, so both arrive at their final position simultaneously. This makes manoeuvring equipment into or out of units simple and safe

Different Sash Materials

Toughened Glass Sash

Sashes are typically constructed from 6mm toughened safety glass. This glass is up to five times stronger than ordinary glass of the same thickness. If it is broken, it shatters into small, blunt chunks, not sharp shards, which are safer to clear up.

Toughened glass is not fire-resistant, but it can withstand temperatures of up to 300 degrees centigrade (570 degrees Fahrenheit). It is always recommended that any ovens or Bunsen burners are situated at least 150mm back from the sash in a fume cupboard.

For added safety anti-shatter film can be provided to hold the glass in place in the event of damage.

Polycarbonate Plastic Sash

Polycarbonate plastic sashes are recommended for fume cupboards which are used for applications using hydrofluoric acid (HF). The hydrofluoric acid fumes can etch glass. Over time this will cause clouding and the need to replace the sash. Polycarbonate is corrosive resistant and will withstand the acid fumes.

Please note: For any application using HF the fume cupboard liner must also be fabricated from a material which is compatible with hydrofluoric acid use.

The Sash Stop

Most fume cupboards feature a sash stop to prevent the sash being raised higher than a defined safe working height when the unit is being used to contain experiments, etc.

The sash stop can generally be overridden to provide extra room for the loading and unloading of equipment and apparatus into and out of the chamber. Fume cupboards should never be operated with the sash in the fully opened position. The sash should always be returned to the safe working level once this operation is completed.

Because fume cupboards dimensions vary, the sash stop will be configured where the face velocity at the working aperture is specified. The clearing rate of the fume cupboard is increased when the sash is lowered.

Most fume cupboards feature a sash stop to prevent the sash from being raised higher than a defined safe working height.

Fume Hood Sash FAQs

Please see a selection of questions that relate to our sash arrangements.

Where should the fume hood sash be positioned?


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.

What are the different sash arrangements available for fume cupboards?


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.

How does a sash contribute to the safety of a fume cupboard operator?


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.

Why are there multiple sash arrangements available?


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.

How do I choose the right Sash?


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.

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