What Is a Fume Hood and When Must You Use One? Guide for Thai Research Labs

If you work with chemicals that generate vapours, gases, or airborne particles, a fume hood is one of the most important pieces of protective equipment in your laboratory. This guide explains what a fume hood actually does, when to use one, how to use it correctly, and what to check to make sure it keeps working as it should.

What a Laboratory Fume Hood Is (and What It Is Not)

A laboratory fume hood is a form of local exhaust ventilation. Its job is to capture and remove airborne contaminants, including vapours, gases, aerosols, fumes, dusts, and powders, before they reach the breathing zone of the person working at it. The extracted air is either discharged to a safe location outside the building or treated and filtered before release.

The protection a fume hood offers is not unconditional. It depends directly on maintaining adequate airflow through the open face, keeping the sash at the correct working height, and avoiding anything that disrupts the air currents inside or around the hood. When those conditions are not met, containment is not guaranteed, regardless of how the hood looks from the outside.

One thing a fume hood should never become

Fume hoods are frequently used as convenient storage shelves for bottles, reagents, and equipment that have no immediate purpose. This is a misuse that degrades performance by obstructing airflow paths and reducing the usable working area. Chemicals stored inside a hood that is not running continue to off-gas into the laboratory. For guidance on proper chemical storage practices, see our hazardous substance storage guide.

A fume hood is not a biological safety cabinet

This is a distinction worth stating clearly, because the two devices look similar from the outside. A biological safety cabinet (BSC) is designed specifically to protect workers from infectious aerosols. It uses controlled directional airflow and HEPA filtration to contain biological materials, and some classes also protect the work product itself from contamination.

Thai laboratory safety guidance from the National Research Council of Thailand's ESPReL programme makes an explicit point of warning that a biosafety cabinet, and a laminar flow cabinet, must not be used as a substitute for a laboratory fume hood. The two devices serve different purposes, and substituting one for the other creates a protection gap. If your work involves both chemical and biological hazards, your facility procedure should address which equipment is appropriate for each task.

When You Must Use a Fume Hood in Thai Research Labs

The clearest starting point for deciding when a fume hood is needed is the SDS for the chemical you are using. Under the Ministry of Industry Notification on Hazard Classification and Communication (B.E. 2555), safety data sheets for hazardous substances are required to include a section covering exposure controls and personal protection, which includes appropriate engineering controls. That section tells you, chemical by chemical, what controls the manufacturer or supplier considers necessary during use.

This means the SDS is not just an information document to keep in a filing cabinet. It is the chemical-specific starting point for deciding whether your planned procedure requires a fume hood, additional ventilation, respiratory protection, or some combination of controls.

Risk assessment as the practical trigger

Beyond checking the SDS, a practical risk assessment of the procedure itself should guide your decision. Procedures that are likely to generate aerosols, such as sonication, homogenisation, and certain centrifugation steps, increase both the likelihood and the quantity of airborne material released. When a procedure creates airborne contaminants, the risk of inhalation exposure rises significantly compared to working with the same material under closed or low-disturbance conditions.

Other factors that should push you toward stronger engineering controls include the inherent hazard level of the material, your confidence that personnel are trained and following the correct procedure, and whether your equipment and facility have any known weaknesses that could increase the chance of a release. If more than one of these factors points in the same direction, the case for working inside a fume hood rather than on an open bench becomes stronger.

International occupational safety guidance describes employer control measures for chemical hazards as including partial enclosure with local exhaust ventilation and general ventilation sufficient to keep worker exposure within acceptable limits. The fume hood sits within a hierarchy of controls: it is an engineering control that reduces reliance on personal protective equipment alone, but it does not necessarily replace other controls. Where the SDS or your risk assessment identifies that additional protection is needed alongside the hood, follow that guidance.

When working with solvents or acids, alkalis, and bases that can generate hazardous vapours, checking the SDS for engineering control requirements before starting work is particularly important. For high-purity analytical work, trace-level contamination from open-bench handling can also affect results, making containment doubly worthwhile.

How to Use a Fume Hood Safely in Daily Work

Getting the benefit of a fume hood depends almost entirely on how it is used. The device can be in perfect mechanical condition and still fail to protect you if common usage errors are present.

Before you start

Check that the hood is working before you begin any procedure. Look at the airflow indicator or alarm, and confirm that the fan is running and that airflow is within the expected range. Many hoods have visual indicators or audible alarms; do not begin work if an alarm is active or if the indicator suggests the hood is not performing correctly.

Run the fan for the manufacturer-recommended period before starting work with any material that generates airborne contaminants. Your facility's SOP and the hood's documentation should specify this. Follow manufacturer instructions on how long to run the fan before and after work.

During work

Keep the sash at the correct working position. The sash serves a dual purpose: it defines the opening through which air is drawn into the hood, and it provides a physical barrier between you and the work. Closing the sash too far may interfere with access; raising it too high reduces airflow velocity at the face opening and compromises containment.

Work in the middle or rear of the work surface rather than right at the front edge. This keeps the work further inside the containment zone and reduces the chance that airborne material will escape through the open face. Minimise the number of times you move your arms in and out during a procedure, as repeated arm movements disrupt the airflow pattern at the face of the hood.

Keep the interior of the hood uncluttered. Bulky equipment, excess materials, and paperwork placed inside can all obstruct the front or rear airflow grilles and create turbulence that degrades containment. Only materials actively needed for the current procedure should be inside the hood during work.

Room conditions that can undermine the hood

The hood does not work in isolation. Room air movements from air conditioners, open doors and windows, nearby cooling fans, and people walking past can all create turbulence at the hood face that disrupts the inward airflow. Position your work so that these sources of disturbance are minimised during critical steps, and be aware of busy traffic routes near the hood.

Make-up air supply to the laboratory also matters. If the room cannot supply sufficient replacement air, the hood cannot draw in the airflow it needs. If your hood has been recently installed or relocated, or if the laboratory's ventilation layout has changed, confirm with your facility manager that the make-up air supply is adequate for the hood's requirements.

For research involving high-purity reagents where open-bench exposure would also risk contaminating analytical results, working inside a properly functioning fume hood protects both the worker and the integrity of the analysis. If you use Suprapur high-purity acids and bases for trace analysis, consistent hood use during preparation is part of maintaining the analytical standard those reagents are intended to support.

Verification, Inspection, and Maintenance: What to Check and How Often

A fume hood that looked good during installation does not stay in that condition indefinitely. Airflow can change as the building ventilation system ages, as other equipment is added or removed from the laboratory, or as filters and mechanical components wear. Periodic verification is how you confirm that the hood is still providing the protection you are relying on.

Performance checks that confirm the hood is working

Visual and qualitative checks are a practical first line of confirmation. A smoke test, in which a small visible smoke source is used near the face and inside the hood, shows whether the airflow pattern is drawing material inward and whether any leakage or eddying is occurring near the breathing zone. A dust-lamp test can reveal escape of fine dust or mist that would not otherwise be visible. These checks are straightforward to perform and can quickly reveal problems that airflow numbers alone might not catch.

Quantitative measurements go further. Measuring airflow velocity at the face and volume flow rates through the ductwork, and comparing those values to the hood's design specification or the benchmarks established when the system was first commissioned, tells you whether performance has drifted. Static pressure measurements at defined test points across the system, including across filters and at the fan, help identify where any degradation is occurring. Fan speed and power consumption can indicate whether mechanical components are ageing or under load.

Where the risk associated with the work is high, air sampling to confirm that actual worker exposure is being controlled to an acceptable level may be appropriate. This gives real-world confirmation that the engineering control is doing its job under actual working conditions, rather than just under test conditions.

Alarm systems should also be tested periodically by simulating the failure condition the alarm is designed to detect. An alarm that has never been tested may not function when it is needed.

What Thai requirements address

The Ministerial Regulation on Hazardous Chemicals (B.E. 2556), issued by the Department of Labour Protection and Welfare, requires employers to inspect and maintain hazardous chemical containers and packaging so that they remain safe to use. Where hazardous chemicals have leaked or are at risk of leaking, the regulation requires prompt cleanup, segregation, and repair or replacement to restore a safe condition. This requirement addresses chemical containers directly, not ventilation equipment.

For specific legal obligations regarding inspection or testing of fume hoods and local exhaust ventilation systems, confirm the requirements that apply to your facility type with your legal or EHS advisor. The scope of applicable regulations can vary depending on whether your facility is classified as an industrial workplace, a research institution, or another category under Thai law.

Regardless of specific legal requirements, regular verification is sound practice for any laboratory that relies on a fume hood as a control measure. A hood that is not verified periodically may have degraded without anyone being aware of it. If performance checks reveal a problem, the hood should not be used for hazardous work until it has been repaired and re-verified. Your facility's maintenance procedure and the hood manufacturer's documentation should guide the specific intervals and methods appropriate for your equipment. For laboratories that also need guidance on storing chemicals safely between uses, our comprehensive chemicals storage guide covers key principles for keeping stored materials under safe conditions.

Frequently Asked Questions