Posted By Ken Price Deal all, I have just been made aware that some of the analysts in the labs are switching off the fume hood before they weigh some particularly toxic compounds. They have to weigh out just a few milligrams at a time and are finding that the balances fluctuate too much when the fume hood is switched on. I'm obviously not happy with the possible exposure to these powders. Has anyone else seen a similar situation? Do you have any suggestions on how they can weigh in a safer way? Do they need to wear special dust masks? Thanks, Ken.

Posted By Stephen D. Clarke Assuming you have an approximate idea of what the required few mgs looks like in terms of volume, spatula this amount into a small pre-weighed/dried etc sealable glass vessel with the fume hood on. Then seal the vessel, fume hood off, weigh precisely what you have. If too much or too little fume hood on, open the vessel, and remove or add a smigen. Time consuming at first but with practice quite effective.

Posted By timwright A few years a go I worked in a lab weighing out very toxic pesticide samples. We also needed to weigh very small amounts and were forever having problems with the fume extraction. To overcome this issue you can do a couple of things. 1. Buy a balance that can cope with flow as was previously suggested. I suspect that with the volumes you are weighing out and the accuracy you need that theses will be very expensive. However you need to balance out the Cost v Risk. 2. Purchase a glove box which you place the balance into, the dusts / fumes are then contained during the weighing operation, and then once you have carried out your weighing and making up of your solutions you then switched on the glove box to extract the fumes etc. Sometimes the glove box was situated inside a fume cupboard, this was switched onwhilst working in the glove box, it did not then effect the sensitivity of the balance whilst you weighed out the substances. Regards Tim Wright

Posted By garyh I echo the last comment. In a previous life I was a "Bench Chemist" (this was before I discovered that Chemists don't get great salaries - so I ended up a Safety Manager? What was I thinking??) We used balances in fume cupboards but they sat within a little glass case with a hinged door and lid........ On the other hand I am not sure it is a big deal about handling toxic powders with the extraction turned off temporarily - unlike gases which escape and diffuse the chemist won't be exposed to the powder unless it is spilt?? Got it! Do a risk assessment!! That always solves all known safety problems!