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Local Exhaust: Household Hazardous Waste Drop-off Sorting Table

Local Exhaust: Household Hazardous Waste Drop-off Sorting Table

Local Exhaust: Household Hazardous Waste Drop-off Sorting Table

I am trying to determine what kind of flow rate is reasonable for locally exhausting (likely with slotted hood at the perimeter) a table used for sorting household hazardous wastes at a public 'eco station'.  The only value I have come across is from the ACGIH design manual at 50-100 CFM/sq.ft of table area but this yields an extremely high exhuast volume for a large table.  Does anyone have any experience with something like or similar to this?  Any advice would be appreciated.  

RE: Local Exhaust: Household Hazardous Waste Drop-off Sorting Table

Can you change the size of your table, making it narrower? Also you may want to consider different hood configurations, depending on how the operation works. Could the hazardous materials be inside a booth for example and still be sorted adequately? Does the exhaust hood need to be working 24/7. Perhaps a 2-speed fan could reduce the amount of air exhausted during off-shift hours.

How large is your table and what type of hood were you considering?

Is this an air conditioned space? Is that why you don't want to exhaust as much air?

Peter Ott

RE: Local Exhaust: Household Hazardous Waste Drop-off Sorting Table

It may be possible that the table can be narrower.  Currently it is a whopping 170 sq. ft.   The type of exhaust I was considering is an exhaust duct running underneath the table with slot exhaust 'hugging' the table from below, exhausting from the perimeter of the table  on both sides (50-100 CFM/sq. ft of table, @2000 fpm).  I can direct you to an ACGIH detail later (if you wish) but I am currently at home

Unfortunately the table needs to be accesible from both sides - the public comes up on one side to drop off the waste and the employees stand on the other side and sort.  This is why I thought the perimeter slot exhaust would be the most suitable as it allows for unobstructed usage of the table.  I had not considered having a temporary 'holding' spot where a fume hood may be practical - that may be a good solution.

What type of hood configurations do you think might be practical?

The reason I want to minimize exhaust air is because I will need to replace the exhasuted air with outside air.  I am writing from Edmonton, Alberta, Canada and high make-up air volume = high energy consumption in winter time.  As well, it seems silly that the local exhaust for a sorting table would be comparable to that of the entire warehouse @ 20,000  CFM (20,000 sq. ft. @ 1 CFM/sq. ft) - but I am a junior engineer so my experience is limited; perhaps it is reasonable.

No cooling is provided to the space; however design winter outside air temperature is about -32 deg. F (not a mistake).

The fans will only be operated during business hours.

I guess my main question remains:

Is 50-100 CFM/sq. ft. of table excessive or reasonable?  Could I go less?

Do you ahve any suggestions for hood types / exhaust strategies?

Your further input would be greatly appreciated.

Mikhael Horvath

RE: Local Exhaust: Household Hazardous Waste Drop-off Sorting Table

Given the type of hood you are envisioning, and I am familiar with the sketch you are referring to in the Ventilation Manual, 50-100 CFM/sq.ft. is not excessive.

However, is a hood necessary at all? Are fumes noticeable?

Have you considered using an enclosed belt conveyor where the public feeds their waste onto the end of the belt and the enclosed belt travels down to openings for sort stations of various waste products? This arrangement could use considerably less exhaust air.

Peter Ott

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