Re: fume hood for balances

From:"Histomail\\" <>

Dear Barbara,
your safety officer may have a valid point. We already know that some dyes
are potentially carcinogenic eg. the Rosanilin derivatives, crystal violet
While the use of a fume cupboard may be very useful for extracting fumes,
they interfere with both the operation and accuracy of the balance, unless
the balance is enclosed such as your Mettler. The risk is in opening and
transferring powdered dyes from the original container to the weighing
vessel- I would make the following points:-
1) Always wear a surgical mask, gloves and apron when carrying out weighing
2) Never use plastic receptacles to transfer or weigh powders, as these may
have significant electrostatic charge, and disperse powder all over the
place even microscopically.
3) If using an extraction device, position so that airflow does not overly
affect performance of balance- the device must not be part of the
construction of the bench. Sealing door slides on a balance are recommended.
4) Ensure all equipment and bench is properly grounded.
5) All used equipment, vessels etc even if disposeable, should be placed
directly into a bucket of cleaning agent (I use Domestos/soap solution) to
wet the vessels etc. to prevent unwanted spread of powder during wash up or
disposal. Also makes washing up easier.

Personal note:- I have used a small perspex box (2x2x2 ft) for weighing
small volumes, the front of which is open , and the rear of which has a
cut-out into which is connected a Phillips Air Purifier for asthmatics
mounted on a foam pad - this is fitted both with and extraction filiter
designed for dust and pollen, and also includes an electrostatic
precipitator. This device is both transportable, and has minimal
interference on the balance performance but is only suitable for masses
2-500g. for masses less than this a balance with closeable slides must be
used.  Your local hanyman can knock one of these up for you in a few moments
for a minimal cost.
I would make a final comment, some will say that only a fume cupboard is
satisfactory, I must empasise that certification of fume cupboards is
carried out when they are empty; and I must say that their performance can
be vastly different with a bulky object placed inside them, and I suspect
offer no advantage over our little home made box!! Besides fume cupboards
are not designed to remove dust!!!
Regards Mike Rentsch (Downunder)

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