April 13, 2011
When it comes to laboratory safety, you should never cut corners to save money.
A few months ago, I had a teflon beaker melt on a yellow hotplate which we had purchased for the lab to replace a hotplate that died. Unfortunately, when inexpensive hotplates “die” they tend to heat up very hot, which can be very dangerous. I’m not sure exactly what happens, but I think that over time acid corrosion affects the thermocouple so that the hotplate can no longer regulate temperature properly.
I use some very strong acids in my chemistry– concentrated nitric acid, hydrofluoric acid, and perchloric acid. I need to use strong acids because I am dissolving rocks. As you can imagine, dissolving rocks is no easy task– those silicate bonds are difficult to break. Because I use such strong, corrosive acids, I think the electronics of an inexpensive hotplate are easily corroded. I wish the hotplate would just switch off or cool down when it becomes corroded. Unfortunately, when this model of hotplate dies because of acid corrosion, it dangerously ramps up in temperature, melting teflon beakers filled with acid and rock powder.
|Good hotplate. Note the lack of melted beakers.|
Most of the hotplates in lab are home-made with heating tape and will not fail in such a catastrophic way. However, these hotplates do not reach high enough temperatures to dry down perchloric acid, which I must use in my dissolutions. I’m not the only one who uses perchloric acid– there are others in the lab who have used this dangerous acid. To dry down perchloric, we use a special venting system (so we don’t inhale the vapors) and use a store-bought hotplate. We’ve been using the Cimarec hotplate made by ThermoScientific. This is a BAD HOTPLATE. I bought a brand-new Cimarec back in October or so, and it has already failed by overheating. The Cimarec we had before that lasted less than a year before it melted a single teflon beaker.
When the beaker melted on the previous Cimarec hotplate, I was very concerned. I was very sad to lose a sample, of course, as my chemistry takes MONTHS so the loss of even a single sample is very unfortunate. The bigger problem, however, is the possible risk of fire by melting a plastic beaker containing very strong acids and rock powder. I looked into what types of hotplates we could purchase that would not fail in such a catastrophic manner. The problem? The “safe” hotplates cost about $3,000 whereas the “unsafe” Cimarec hotplates cost only about $300. My primary advisor had just left for another institution, so there was no way that he was going to buy a $3,000 hotplate to leave behind. The lab technician advised that I buy another Cimarec since “it was unlikely” that it would fail again before the labwork for my thesis was completed. I listened to the lab technician and my one advisor (I’ve got two actually), which was a mistake. I should have insisted that we purchase the expensive hotplate. Or I should have insisted that I be allowed to dry down my perchloric samples in another lab with safe hotplates.
But I bought the new Cimarec hotplate and the technician helped me install it. I did change my behavior– I didn’t leave the hotplate alone during the day, and I switched it off overnight. However, I didn’t watch it every minute– it’s just not practical to do so.
Today the inevitable happened. I put two 120 mL teflon beakers and their lids on the yellow hotplate to dry down. I went to work on something else in the lab, but after about 30 minutes I smelled some smoke. This is what I found:
|Note the lowness of the temperature dial. I had it set to 125 deg C, well below the melting point of teflon plastic.|
|Only a beaker lid rim remains.|
|Bad teflon goo.|
I immediately unplugged the hotplate and called security. No one was hurt, and there was no fire. But someone could have been hurt, and there could have been a fire. I have already filed an extensive safety report and plan to meet with the safety officers in the near future. Although a new, fancy hotplate may not be installed in time for my thesis work, I plan to do everything possible to make sure that an expensive but safe hotplate is installed. There is a new scientist about to take over the lab (a replacement for my advisor), and he agrees with me. He made a fuss about the hotplate as well, and he’s trying to insist that his start-up allow for the purchase of several of the expensive but safe models of hotplate. I hope that the accident today gives him leverage to insist on the money he needs for the safe hotplates.
This time, I think my advisor and the lab technician will take my request for an expensive hotplate seriously. If not, an accident like this may happen again. After all, those who do not learn from history are doomed to repeat it. If any of you use the Cimarec hotplates to dry down acids, please seriously consider abandoning use of this type of hotplate.
As for my chemistry? I’ve already asked the scientist across the hall if he would dry down my samples for me in his expensive dry-down system. He has generously agreed and also offered to help me insist that the lab (which is going to be rebuilt for the new scientist) contain the safe hotplates.
A final note is that I am mourning the loss of the two peridotite samples that melted earlier today. I had been dissolving these samples for several months, so I’ve now lost months of chemistry. Fortunately, I only lost two samples.