Ductless Fume Hood Applications and Filter Selection Guide

A ductless fume hood is a laboratory safety device that does not require external ductwork and purifies hazardous gases and particulates through a built-in filtration system. Compared with traditional ducted fume hoods, ductless fume hoods offer advantages such as flexible installation, energy efficiency, environmental protection, and convenient maintenance.

By properly selecting filters, ductless fume hoods can effectively adsorb toxic and hazardous gases, volatile organic compounds (VOCs), acid and alkaline vapors, as well as airborne particles generated during laboratory operations, providing a safer and cleaner working environment for laboratory personnel.

1. Applications of Ductless Fume Hoods

Applicable Industries

Ductless fume hoods are widely used in:

• Research institutes

• Universities and colleges

• Inspection and quarantine institutions

• Healthcare and medical facilities

• Food industry

• Pharmaceutical industry

• Environmental monitoring institutions

• Chemical industry

• Petroleum industry

• Electronics manufacturing

• Military industry

• Hospital laboratories, etc. 

They are especially suitable for:

• Laboratories without external exhaust systems

• Temporary laboratory areas

• Small laboratories

• Energy-saving laboratory renovation projects

2. Scope of Application

Ductless fume hoods are suitable for approximately 99% of common laboratory chemicals, including:

• Organic solvents

• Acid and alkaline gases

• Volatile organic compounds (VOCs)

• Certain toxic vapors

• Dust and particulate matter

However, the following chemicals and operating conditions are not recommended for use in ductless fume hoods.

3. Chemicals and Applications Not Recommended

LIST OF CHEMICALS NOT RECOMMENDED*

(1) Gaseous Chemicals with Very Low Boiling Points at Normal Temperature and Pressure

These gases are highly volatile and cannot be effectively adsorbed by activated carbon filters, making them unsuitable for ductless fume hoods.

Examples:

• Hydrogen (H₂)

• Helium and noble gases

• Methane

• Methyl iodide

• Methyl bromide

• Thionyl chloride

• Ethane

• Ethylene oxide

• Carbon monoxide

• Carbon dioxide

• Nitrogen monoxide

• Propylene

• Propyne

• Acetylene

(2) Highly Toxic Chemicals

A.Organophosphoric Compounds

Due to their extremely high toxicity, some compounds may even be used in chemical weapons applications and are therefore not recommended for use in ductless fume hoods.

B.Mercury

Mercury vapor is highly toxic and extremely difficult to detect.

The TLV (Threshold Limit Value) is only 0.05 ppm.

C.Hydrogen Cyanide

Hydrogen cyanide is immediately lethal and classified as an extremely hazardous gas.

(3) High-Risk Heating Experiments

The following experiments may generate large quantities of strong oxidizing, toxic, or uncontrollable gases and are therefore not recommended:

• Heating experiments involving hydrogen peroxide

• Heating experiments involving hypochlorous acid

• Strong oxidizing reaction experiments

• Experiments involving violent decomposition reactions

4.Filter Selection for Ductless Fume Hoods

The filtration system is the core component of a ductless fume hood. Different filters should be selected according to the types of contaminants generated during laboratory operations to ensure optimal purification performance and laboratory safety.

5. Common Filter Types and Their Applications

(1) HEPA (High Efficiency Particulate Air) Filter

A.Function

Used for filtering airborne particles, dust, and microorganisms.

B.Filtration Efficiency

Equipped with an H14 HEPA filter capable of removing particles larger than 0.3 μm with an efficiency of over 99.995%.

C.Typical Applications

• Powder handling

• Particle-related experiments

• Biological particle filtration

• Dust-generating environments 

(2)Organic Gas/Vapor Filter

A.Function

Used for adsorbing organic gases and volatile organic solvents.

B.Applicable Chemicals

• Carbon tetrachloride

• Carbon disulfide

• Chloroform

• Chloromethane

• Nitroalkanes

• Benzene

• Acetone

• Alcohols

• Aniline compounds

• Chloropicrin

• Toxic smoke and toxic mist

C.Typical Applications

• Organic chemistry experiments

• VOC handling environments

• Solvent preparation

• Volatile organic compound processing 

(3)Inorganic Gas/Vapor Filter

A.Function

Used for filtering toxic inorganic gases and vapors.

B.Applicable Chemicals

• Hydrogen cyanide

• Hydrogen chloride

• Chlorine

• Arsine

• Phosgene

• Diphosgene

• Bromine

• Dichloromethane

• Lewisite

• Mustard gas

• Phosphine, etc.

C.Typical Applications

• Inorganic chemistry experiments

• Toxic gas handling

• Special chemical processing environments 

(4)Acid Gas/Vapor Filter

A.Function

Used for filtering acidic and corrosive gases.

B.Applicable Chemicals

• Sulfur dioxide

• Chlorine

• Hydrogen sulfide

• Phosgene

• Nitrogen oxides

• Chlorinated organic pesticides, etc.

C.Typical Applications

• Acid-base experiments

• Corrosive gas environments

• Chemical laboratory applications 

(5)Ammonia and Hydrogen Sulfide Filter

A.Function

Specially designed for filtering ammonia and hydrogen sulfide gases.

B.Applicable Chemicals

• Ammonia

• Hydrogen sulfide

• Toxic smoke

• Toxic substances

C.Typical Applications

• Ammonia-related experiments

• Sulfide experiments

• Odor control applications

(6)Universal Carbon Filter

A.Function

Capable of filtering:

• Organic gases

• Inorganic gases

• Acidic gases

• Ammonia

• Hydrogen sulfide and other contaminants

B.Typical Applications

Suitable for laboratories handling multiple chemical categories or where contaminants are not clearly defined.

C.Important Notes

The following gases cannot be effectively adsorbed or catalytically filtered by activated carbon:

• Carbon monoxide

• Nitrogen

• Hydrogen

• Inert gases

D.Typical Filterable Chemicals

Organic Chemicals:

Carbon tetrachloride, carbon disulfide, chloroform, benzene, acetone, alcohols, etc.

Inorganic Chemicals:

Hydrogen cyanide, hydrogen chloride, chlorine, phosgene, phosphine, etc.

Acidic Chemicals:

Sulfur dioxide, chlorine, nitrogen oxides, etc.

Ammonia & Sulfide Chemicals:

Ammonia, hydrogen sulfide, etc.

(7)Formaldehyde Removal Filter

A.Function

Specially designed for efficient adsorption and decomposition of formaldehyde gas.

B.Typical Applications

• Pathology laboratories

• Formalin-related experiments

• Specimen preservation

• Formaldehyde handling environments 

(8)Pre-Filter (Primary Filter)

A.Function

Used for capturing large dust particles to protect the main filter and extend its service life.

B.Filtration Efficiency

Equipped with a G4 primary panel filter capable of removing particles larger than 10 μm with an efficiency of over 95%.

C.Typical Applications

Suitable for front-end air pre-filtration in all ductless fume hoods.

6. How to Properly Select Filters

When selecting filters for a ductless fume hood, the following factors should be considered:

(1) Chemical Type

Different chemicals require different filters:

• Organic solvents → Organic filters

• Acidic gases → Acid gas filters

• Ammonia → Ammonia filters

(2)Chemical Concentration

High concentrations of volatile chemicals may require:

• Higher-grade filters

• Higher airflow systems

• More frequent filter replacement

(3)Experimental Temperature

High temperatures accelerate chemical volatilization and reduce activated carbon adsorption efficiency. High-temperature experiments should therefore be carefully evaluated.

(4)Mixed Chemical Applications

If multiple chemicals are used simultaneously, a universal filter is recommended, or a professional filter configuration assessment should be conducted.

7. Conclusion

With advantages such as no external ductwork requirement, flexible installation, energy efficiency, environmental friendliness, and easy maintenance, ductless fume hoods have become an important part of modern laboratory safety systems.

Proper risk assessment, correct filter selection, and avoiding unsuitable chemicals and high-risk operating conditions are essential to ensuring the safe and efficient operation of ductless fume hoods.