How to Use a Fume Hood: Its Parts and Rules for Safe Work

Even a well-chosen fume hood cannot protect its user if it is used incorrectly. Airborne contaminant particles cause harm when inhaled; with the inhaled air, chemicals can reach the lungs and from there enter the bloodstream and spread through the body. This article first describes the parts of a fume hood and then summarises the rules for using it safely.

Parts of a Fume Hood

• Body: the enclosure that contains hazardous gases and vapours.
• Baffles: movable panels that form slotted openings along the back panel. They keep the airflow even across the opening, eliminate dead spots and improve capture efficiency.
• Sash: adjusts the front opening so that the airflow is set to the point where contaminants are captured best. Every fume hood is marked with its optimum sash position. When the fume hood is not in use, the sash should be kept fully closed.
• Airfoils: profiles along the bottom and side edges that smooth the incoming airflow and prevent turbulence that could carry vapours out of the hood. The gap beneath the bottom airfoil lets room air in even when the sash is fully closed.
• Work surface: the base on which instruments are placed, usually a worktop.
• Exhaust plenum: helps distribute the air evenly across the opening. Materials such as paper towels drawn into it cause turbulence in this part of the hood, leading to weak airflow and uneven performance.

Positioning

• Place the fume hood away from fresh-air inlets, doors and windows, where there is the least traffic.
• Do not install it in very dusty, humid or hot locations.
• It must be connected to an earthed electrical installation.

Before You Start

• Human error is mainly caused by a lack of knowledge about the chemical being handled and by carelessness. Keep a list of the chemicals to be used, with their safety data sheets, close at hand.
• Switch on the extract fan before opening the sash.
• Before starting work with explosive or flammable chemicals, make all the electrical equipment connections that will be needed and switch the equipment on.

While Working

• Keep all materials at least 15–20 cm back from the front edge of the fume hood.
• Work with as few materials inside as possible, and do not place them in front of the heavy-gas panel.
• Keep the sash as low as the work allows. This protects the user from any explosion, flash or splash inside the hood.
• Do not raise the sash above 50 cm while working; otherwise the extraction weakens and the gases released can escape from the enclosure.
• The sash offers protection, but personal protective equipment such as gloves, safety goggles and a face shield is still required.

Emergency Preparedness

When working with sodium hydroxide, potassium hydroxide, calcium hydroxide and similar substances, keep an eye and body shower nearby, together with 1% boric acid and 5% acetic acid solutions, for any burns that may occur.

Which Substances Must Be Handled in a Fume Hood?

A fume hood must always be used when working with corrosive, toxic or carcinogenic substances such as nitric acid, sulphuric acid, hydrochloric acid, sodium hydroxide, potassium hydroxide, mercury, carbon tetrachloride and ammonium dichromate.

KRCLAB fume hoods have a stop that prevents the sash from opening more than 50 cm, together with “50 cm sash opening” and “keep sash closed” warning labels.