From sci.chem Tue Nov 19 13:56:21 1996 Newsgroups: sci.chem From: B.Hamilton@irl.cri.nz (Bruce Hamilton) Subject: Re: Lab Accidents....... Message-ID: Date: Sun, 17 Nov 1996 11:36:47 LOCAL Thanks to both of you. Alas, most of my experiences have been in the world of commercial laboratories and pilot plants - the following spring to mind. At school we moved into brand new teaching labs, and one experiment involved sulfur and a deflagrating spoon ( something I've never seen since ). The teacher demonstrated the experiment, and told us to immediately quench the hot spoons in the sink. We did, and over half the sinks then had nice round holes through them - he forgot that the new lab had plastic sinks in place of the old metal ones. Whilst overseas, I worked for a small company, and one of my jobs was helping the Formulations Chemist, who happened to be working on Animal Feed mixtures - thick brown sludge that was dried impressively in the new larger Fluidised Bed drier. You probably know the type, just like a large hand-drying hot-air blower pointing upwards, where you load the sludge into a bag somewhat similar to a horse's feeding bag, and clip that around the nozzle. You turn up the fan and the bag ballons up and then vibrates as the drying material bounces off it. It was the pride of the lab. Well, I carefully prepared the formulation and was spooning it in when the company General Manager arrived with some important potential clients. The Formulation Chemist quickly arrived and took over, so I duly retired to the back of the lab. He finished filling it, connected it and turned on the drier, all the while talking to the manager and guests about how wonderful the new drier was for development work. He wound up the air speed and the bag danced even more impressively. Suddenly the room was filled with a huge, high- velocity brown sandstorm as the bag slid off the clip. Almost everyone and everything was instantly covered with 2 kilos of thick brown dry sludge. There, but for the grace of God, go I... One of my bosses taught me never to assume that the details of a chemical synthesis in peer-reviewed literature were sufficient. He had an article with a detailed description and drawing of the complex equipment required for a large scale synthesis. He made it exactly as specified, looked at the completed work, and discovered there was no vent. He and other senior experts came to the conclusion that gases produced were condensed or absorbed into one of the several solutions present. To be on the safe side, he took off a clip on one of thermometer wells - if the pressure built up too much, the well should lift and vent. He started the reaction, when it finally exploded, it annihilated all glassware on that side of the lab. Ground glass joints condense liquid in them, and the surface tension then holds the joint against relatively high pressures - they don't make good pressure relief devices. The author of the paper subsequently reported that the vent had inadvertly been omitted from the illustration. One of my colleages was known for his parsimoniousness. Whenever he went to the cold, concrete solvents store, he would fill the winchesters to the brim, and still mark down 2 litres. One day he brought the two acetone winchesters back and put them on the bench, and went off to morning tea. The bottom was pushed out of them by hydraulic expansion as they warmed up to laboratory tempertures, and 5 litres of acetone surged across the bench looking for a source of ignition. When he came back, he wasn't even concerned about the potential fire hazard, he was beside himself that he had lost 5 litres of acetone that he had signed against his project. One of my jobs was to make trial batches of rigid polyurethane foam. This was achieved by using a hand-held high-speed electric drill with a paint-mixer paddle. The two components were poured together, mixed for about 10 seconds less than the cream time ( usually about 15sec ), and quickly poured into a plastic bag in a heavy wooden jig and the jig quickly sealed. The foam would expand for about 30 seconds to fill the jig, and then go hard. The equipment had to be rinsed with trichloroethylene within 30 secs, otherwise the foam would harden, and the only other way to quickly clean it was to burn it off. Somehow, I got the formulation very wrong, the cream time was only a few seconds and there was no way I was going to get it anywhere near the jig, and the free-rise density was very low, meaning I was soon going to have a large volume rapidly enveloping me. The small beaker of cleaning trichloroethylene made minimal impact on the rapidly-growing blob, I quickly grabbed the pail, rushed outside ( whilst spreading growing brown foam flecks all around me, and dumped the whole lot into a large, fortunately near-empty, rubbish skip, where it proceeded to grow to occupy a large volume. I quickly cleaned up all traces of my flight, and burnt the equipment clean. It was entertaining watching the rubbish truck driver trying to shake the rubbish into his compactor later in the week. My strangest case was when I was making carbonyl-free acetonitrile for formaldehyde determinations. I was distilling five litres of the acetonitrile/perchloric acid/2,4-dinitrophenylhydrazine, and had finished the distillation, removed the collecting winchester, used a small conical flask to catch any residual condensate, and turned the heating mantle off. I was standing in an adjacent laboratory when I heard an unusual "woosh". I rushed in to find flames throughout the fume cupboard. I used an extinguisher to put the fire out, and there was a strange burn pattern down the flue to the cupboard, and in the cupboard were the partially burnt and shredded remains of a party balloon. The centrifugal fan for the cupboard was on the roof, and the drain plug had never been removed. Some solvent vapours could have accumulated and condensed in water the drain. Not really a problem ( they probably would have evaporated on a hot day ), except for the balloon. The helium line in the laboratory had been used to fill some balloons for some celebration, and one had escaped. It eventually was sucked into the fumehood, and may have been sucked into the fan, which stalled, overheated, and ignited the liquid - which then flowed down the flue and ignited the acetonitrile. Needless to say, the safety officer decided otherwise, and concluded that the balloon was not involved, and that I had left the experiment unattended and operating, the fire started in the heating mantle ( which had no fire damage ), and the flames ignited some solvent in the fan, and that caused the motor to burn out. Just to be on the safe side he took the drain plugs out of the other fans - and some pretty evil stuff came out of them. Naturally, I prefer my version, but you can choose.... Bruce Hamilton