lev....beyond the basics

LEV....BEYOND THE BASICS

ADRIAN SIMS BSc. (Hons) CoC (Control) MFOH(S) MILEVE

DIRECTOR of VENT-TECH LTD

LEV....BEYOND THE BASICS

• Adrian Sims

• Director of Vent-Tech Ltd

• Member of Institute of LEV Engineers

• CoC in Control

• Specialist Member of Faculty of Occupational Hygiene

Focusing more on

• real-world, • retrofitted, • non-ideal systems

“that we occupational

hygienists come across on site”

“were a bit confusing on how to assess appropriately” “not covered

in the P601 or W505

courses”

EXAMPLE 1Canopy hood above waste drip reception

tray to capture vapours and mists arising

• Where would the Capture Velocity reading be taken?

• Is there a need to take a Face Velocity across the canopy hood face?

• Is there a Face Velocity recommended minimum level for a canopy hood?

• What are further control recommendations? i.e. extend hood, side shields, etc.

EXAMPLE 2Extraction hood to band saw for wood

cutting• Where would the Capture Velocity reading

be taken? At the blade?

• As per HSG 258, “Contaminant cloud release into turbulent air with high energy*- Capture Velocity range is 2.5 to10 m/s” If a reading of 6m/s was taken from the blade, should the system be deemed unsatisfactory?

• Where between 2.5 &10 m/s would the Capture Velocity recommendation lie? Would a tyndall beam be a more indicative test than a Capture Velocity reading in this case?

EXAMPLE 2Extraction hood to band saw for wood

cutting• *These types of clouds are difficult to

control using capturing hoods. Would a receptor hood be more suitable? How would this be designed for this process?

• What are further control recommendations?

EXAMPLE 3Full enclosure shot

blaster

• Would a Capture Velocity / Face Velocity reading apply? If so, where?

• Would it be more conclusive to do a smoke test along the seals to show pull inwards into enclosure and prove negative internal pressure?

• Should there be ports across the filter at the back of the unit present, what static pressure readings would be considered satisfactory?

• What are further control recommendations? i.e. suitable clearance period?

EXAMPLE 4Dual hood extraction

to printing stamp

• Can two hoods be better than one?

Would the two systems only work best if directly side by side and not across from or opposing each other?

• In this case, a Capture Velocity was taken at the stamp in the middle (source of vapour hazard) and showed a reading much lower than the two hoods’ Face Velocities.

EXAMPLE 4Dual hood extraction

to printing stamp

• Smoke test showed contradicting pull to the right or left of the stamp.

Would the best recommendation be to rid the system of the second hood and just use one on one side? Or to position both hoods closer together to the stamp?


EXAMPLE 5Extraction of MWF mist

from metal turning machine

• Plastic sheets have been fitted to the system to create a partial barrier to aid in control.

Due to the size and need for accessibility to the machinery (loading, unloading parts), it may not be practical to add further barriers.

Velocities at the centre of the turning mechanism (source of mist hazard) are low, 0.3 m/s.

The turning point is too far from the extraction inlet (outside of it’s capture range). Should the system be deemed unsatisfactory due to poor design?

EXAMPLE 5Extraction of MWF mist

from metal turning machine

• What system would be best suited for this process? A full enclosure may not be practical.


HOW ABOUT…

RECURRING THEME• Prove control using smoke and dust lamp

• Check face and transport velocities together with pressures

• Compare with commissioning data / previous readings (if possible) to look for deterioration

• Recommend containment as much as possible

HSG258

• G??

lev....beyond the basics

Engineering