A ductless fume hood, also known as a filtering fume hood or self-cleaning fume hood, is an innovative laboratory equipment that directly purifies harmful gases inside the cabinet through an internal filtering system without the need for external pipelines. It not only effectively protects laboratory personnel from harmful substances, but also significantly reduces laboratory energy consumption, making it an important equipment in modern laboratories.

01 Technical Principles and Design Features

The core working principle of ductless fume hood is based on the combination of built-in fan system and high-efficiency filtration technology. When the device is started, the top fan will create a stable negative pressure environment inside the cabinet, and the laboratory air will be sucked into the cabinet through the operating port, forming an invisible air barrier that effectively prevents pollutants from leaking out of the cabinet.

The airflow inside the equipment follows a scientific airflow path design. After entering the cabinet, the air will pass through the primary filter, HEPA high-efficiency filter, and specially designed activated carbon filter in sequence. The primary filter is mainly responsible for intercepting larger particles; HEPA high-efficiency filters can intercept particles with a diameter of ≥ 0.3 microns, with an efficiency of up to 99.995%; Activated carbon filters are specifically designed to adsorb volatile organic chemicals and harmful gases.

This multi-layer filtration system ensures the cleanliness of the discharged air, and the purified air is directly returned to the interior of the laboratory, forming a complete internal circulation system. This design eliminates the complex piping engineering required for traditional fume hoods, making equipment installation and position adjustment exceptionally easy.

02 Main Types and Classification Standards

According to the different protected objects and airflow modes, ductless fume hoods can be divided into three categories. The operator protective equipment adopts negative pressure design to prevent harmful gases from leaking out of the cabinet and protect the safety of experimental personnel. This type of equipment can be further divided into vertical laminar flow, horizontal laminar flow, and non laminar flow series, which are suitable for different experimental scenarios.

The sample process protection type fume hood mainly focuses on preventing contamination of experimental samples, maintaining a positive pressure environment inside the cabinet, and preventing external air from entering. This type of equipment can provide ISO5 level (Class 100) clean operating space for the experimental area, suitable for experimental operations that require high cleanliness.

The dual protection equipment for operators and samples combines the advantages of the former two, ensuring both personnel safety and sample purity through a dual filtration system. Its typical representative is the ultra clean safety cabinet, which can be operated without gloves and can accurately control the humidity environment.

According to international standards, ductless fume hoods can also be classified into DH II and DH III equipment. DH III level equipment is equipped with filter groups on both sides of the exhaust fan, which has higher filtering performance and safety.

03 Performance Advantages and Technical Features

Due to the absence of the need to exhaust indoor air conditioning air to the outside, it can save over 90% of air conditioning energy consumption, with an energy-saving efficiency of over 70% compared to traditional full exhaust fume hoods. The power requirement for the equipment fan is relatively low, further reducing operating costs.

Flexibility and convenience are another major highlight. The tubeless design allows the equipment to work with just one power outlet, and can be deployed in any location in the laboratory, even equipped with a roller cart for easy movement. This feature is particularly suitable for laboratory environments with limited space or frequent layout adjustments.

In terms of intelligent control and safety monitoring, modern equipment is equipped with intelligent sensors and control systems, which can monitor surface wind speed, filter saturation status, and air quality parameters in real time. When the filter needs to be replaced, the system will automatically sound an alarm to ensure safe and reliable operation. Some devices also support remote monitoring function, which facilitates real-time monitoring of device operation status.

Environmental friendliness is also an important advantage of ductless fume hoods. The equipment uses environmentally friendly materials such as activated carbon to adsorb chemical substances, and the adsorbed filter will not pollute the environment after professional treatment. At the same time, as it does not exhaust to the outside, it also avoids secondary pollution to the atmosphere.

04 Application Scenarios and Scope of Application

Tubeless fume hoods have been widely used in multiple fields. In the fields of pharmaceuticals and life sciences, it is used for routine operations such as weighing, packaging, and dissolution to protect personnel from exposure to harmful substances. Educational research institutions utilize its flexibility to conduct teaching demonstrations and basic research, without the need for complex installations to obtain security protection.

In the field of chemical analysis, it is suitable for sample pretreatment, titration, trace sample reaction and other operations. For industrial quality inspection and environmental monitoring, it can provide a safe operating environment for instrument analysis, such as high-performance liquid chromatography, COD experiments, etc.

It should be noted that for experiments with mild to moderate chemical loads, the number of chemicals involved in each application should not exceed 10, and the volume is usually less than 500 milliliters. For experiments involving a large amount of highly corrosive and toxic substances or requiring heating treatment of a large amount of chemicals, traditional ducted fume hoods may be more suitable.

05 Selection and Maintenance Points

Choosing the right one requires consideration of multiple factors. The selection of filters is crucial, and specialized filters should be chosen based on commonly used chemical types - universal filters have strong adsorption capacity for acidic gases, while organic filters are optimized for organic gases.

Technical parameters cannot be ignored either. It should be able to provide a stable surface wind speed of 0.4-0.6 meters per second, with noise control below 54 decibels, and equipped with a VAV (Variable Air Volume) control system that can automatically adjust the air volume according to operational requirements.

Daily maintenance is the guarantee for ensuring the long-term stable operation of equipment. Regularly check the saturation status of the filter and replace the failed filter material in a timely manner. At the same time, keep the airflow around the equipment unobstructed and avoid placing it at the entrance or in high traffic areas to avoid affecting the ventilation effect.

Modern equipment is usually equipped with intelligent monitoring systems that can display laboratory pollution status in real-time in PPM units. Users can set their own alarm points to further improve laboratory safety levels. These features make device maintenance more convenient and precise.

With the deepening of the green laboratory concept, the application prospects of ductless fume hoods are very broad. Its modular and intelligent development will further reduce operating costs and improve safety performance. In the future, intelligent ductless fume hoods combined with IoT technology will become standard equipment in laboratories, providing more comprehensive and reliable safety protection for laboratory personnel through remote monitoring of equipment operation status and big data analysis.