Fume hoods 2 min read
The parts of EN 14175, why face velocity matters, the safety features of the sash, and what smoke, tracer gas and face velocity tests show you in practice.
Whether a fume hood protects its user is decided by the airflow across its opening. That is why EN 14175 addresses fume hood airflow through both type tests and tests carried out on site.
The Parts of EN 14175
- EN 14175-1: Vocabulary and dimensions
- EN 14175-2: Safety and performance requirements
- EN 14175-3: Type test methods
- EN 14175-4: On-site test methods
- EN 14175-5: Recommendations for installation and maintenance
Why Airflow Velocity Matters
The fume hood control panel has airflow velocity meters with precision sensors, calibrated to EN 14175-3. The optimum average face velocity is 0.5 m/s at a sash opening of 50 cm. The working opening should not exceed 500 mm and the average face velocity should not exceed 1 m/s; otherwise turbulence can cause toxic gas to escape.
Sash and Safety Features
- The sash moves up and down on a special mechanism without projecting beyond the dimensions of the fume hood.
- It stays at whatever height it is released and is easy to move. It runs in a channel on wheels and guides within an aluminium frame.
- It is made of explosion-resistant 5 mm toughened glass or 6 mm safety glass.
- As EN 14175 requires, it carries “50 cm sash opening” and “keep sash closed” warning labels.
- A stop prevents the sash from opening beyond 50 cm, and a suspension safety system stops it from falling if the cable or mechanism fails.
How Performance Is Tested
Smoke Test
A visible gas is released into the fume hood and the airflow pattern is observed. The air should enter the enclosure smoothly and be carried by the baffles into the exhaust duct; any escape into the room, or dead zones created by turbulence, are unacceptable. Because the human eye can perceive only about a hundred of every million smoke particles, this test is subjective.
Tracer Gas Test
To understand the air distribution in critical zones precisely, quantitative tests that give numerical results by the tracer gas method are needed.
Face Velocity Measurement
The velocity is measured at points on an evenly spaced grid across the fume hood opening and averaged. This measurement gives information on the velocity profile and turbulence and is suitable for quick checks, but it does not show the air distribution in critical zones.
Take the Room Into Account
For a reliable assessment, air movement, temperature and pressure fluctuations in the room, the position of the fume hood and the materials inside it must also be taken into account.
Every fume hood KRCLAB manufactures is airflow-tested to TS EN 14175.
