User safety in oven operation
When using a laboratory oven, it is best to avoid burning yourself. It’s obvious, but needs to be said. Think about your busy morning; when you pull up to the fast food drive-thru, flustered and eager at 7 am for coffee and a breakfast sandwich, what do you do? Chances are, you drive away one-handed, gripping change in your fist while the coffee cup goes between your legs. You don’t even think about it; you’ve got too many other distractions and somewhere else to be. Science is like that, too. You’ve got four experiments running simultaneously, and the oven timer says your glassware is done drying. While a coffee might be 70 or 80 degrees Celsius, a laboratory oven can be as hot as 300 degrees Celsius. As such, it is imperative to wear appropriate personal protective equipment when using the oven (including thermoprotective gloves and a lab coat), and to stand to the side when you open the door.
It is equally important to avoid exposure to toxic vapors and fumes. If you forget about residual organic solvents coating your glassware, or use the oven mistakenly to dry volatile or toxic samples, all the fumes will remain in the heated chamber. After all, it’s not a fume hood, and unless it’s customized to connect to a ventilation source, guess where it will vent? In your face, all at once, when you open the door (wait a second—you stood to the side, right?). Alternatively, it may ignite and burst into flames. Therefore, it is important to always understand the chemical properties of the samples you put in an oven, to rinse glassware several times with distilled water, and to double-check that what you thought was clean before you bake it is, in fact, clean.
Convection ovens—safety standards and options
Laboratory ovens occupy two categories: convection ovens and vacuum ovens, and the former can be further subdivided into 1) gravity or natural, and 2) mechanical or forced convection ovens. Vacuum ovens usually serve specialized functions, such as outgassing solvents during procedures that require a high degree of environmental control. For the comparatively mundane functions of drying and heating samples, or preparing glassware for sterile use, convection ovens are standard. A gravity oven allows heated air to naturally expand, rise, and equilibrate an internal space to a desired temperature. It is a cheaper, albeit less versatile option than most mechanical ovens, which employ a blower fan to distribute heated air around the chamber.
Both types of convection oven should adhere to approved engineering and safety standards. These include the 2007 updated DIN 12880 international standards for temperature stability and homogeneity, and the UL 61010-1 certification mark for safety in electrical equipment pertaining to control, measurement, and laboratory use. Additionally, ovens should have automatic shutoff, door lock, and alarm systems for over- and under-temperature situations. Just like with any laboratory equipment purchase, there are a variety of options ranging in features in price. The Thermo Heratherm top-of-the-line series is the Advanced Protocol Security Model, which comes replete with safety features and is available in sizes up to 750 liters, which requires a 400-volt electrical connection.
Keep in mind, however, that even the best mechanical convection oven is optimized to protect the sample before it protects you, a potentially vexing hierarchy. The best thing you can do to protect yourself is read the user’s manual, which contains numerous key safety warnings, and acts as the best guide to train all laboratory members and inform them of potential risks.