Mercury safety hazards

Mercury Thermometers. In the past, mercury thermometers were by far the most common type of laboratory thermometer. Concerns about health hazards associated with mercury have now reduced their role. However, when high precision is required (calorimetry and freezing-point depressions, for example), oil-in-glass thermometers are not suitable since the use of fine capillaries is not feasible with oil. Furthermore, the safety hazards involved in the laboratory use of mercury thermometers are quite low, as discussed at the end of this section. For these reasons, a description of the use of mercury thermometers is still pertinent. 

Two very different kinds of pump fluids have been employed in diffusion pumps. For many years, mercuiy diffusion pumps, were used in small laboratory-bench glass vacuum systems. Mercury pumps are now seldom used owing to the health hazards associated with mercury and the high probability of contamination of the vacuum system with mercury unless a cold trap is used (the vapor pressure of mercury at room temperature is —1.5 mTorr). The oil diffusion pump eliminates the safety hazard and can serve for both small glass and larger metal vacuum systems. 

Mercury Manometers. A U-tube manometer filled with mercury is simple to construct, requires no calibration, and operates over a wide pressure range. It is now less frequently used due to concerns about safety hazards associated with mercury (see Appendix C) and its slow visual readout. However, it is a historically important device and it is directly related to barometers, which are discussed in Chapter XIX. 

Steere, N.V. 1971. Mercury vapor hazards and control measures. In Handbook of Laboratory Safety, second edition. N.V. Steere, ed., pp. 334-341. Boca Raton. FL CRC Press. 

To clean a metal diffusion pump, it must be removed from the rest of the system. Pour the used oil (or mercury) into a proper receptacle. Do not throw the mercury away because it is a toxic waste (a heavy metal). Fortunately, mercury may be reclaimed and reused. As far as diffusion pump oils, check with the health and safety and/or environmental officer in your institution and/or the waste disposal management of your city. Be sure to mention any hazardous materials that may have been absorbed by the pump oil during its operation to the proper authorities. 

Hazards Place the test tube behind a blast shield during the reaction for safety. Use proper ventilation when handling ammonia, and avoid inhalation of the fumes. Be aware of potential formation of mercury vapor, and use great care. As with any chemical reaction, pay attention and stay focused on what is going on, and what you are doing. 

In recent years, there has been considerable stress on the potential health hazards of oral mercury thermometers used for medical purposes. In fact, the risk of mercury poisoning from a broken mercury thermometer in a physical chemistry experiment is extremely low. The key safety rule if such a thermometer were to break is the prompt and efficient cleanup of any spilled mercury see Appendix C for further details. Note that essentially no mercury will be spilled if the stem rather than the bulb is broken. In conclusion, mercury thermometers should be handled with reasonable care, but they are useful and precise scientific instruments of considerable value for research applications. 

SAFETY PROFILE Poison by intraperitoneal route. Moderately toxic by ingestion. Mutation data reported. A very dangerous fire hazard when exposed to heat, flame, or by chemical reaction with oxidizers. A severe explosion hazard when shocked or exposed to heat or flame. It is about as powerful as TNT. It is normally mixed with coUoided nitrocellulose or ammonium nitrate and paraffin wax. Can react vigorously with oxidizing materials and the derivatives can be explosive. The mercury and silver salts and other derivatives are much more impact-sensitive. When heated to decomposition it emits highly toxic fumes of NOx. See also NITRO COMPOUNDS. 

In 1982, the European Union s Council Directive 82/501/EEC on the major-accident hazards of certain industrial activities, also known as the Seveso Directive, was adopted. The Directive was mostly designed to promote information flow and created the requirement that each Member State (i.e., each country belonging to the European Union) appoint a Competent Authority to oversee safety issues. The Seveso Directive was amended twice, following major accidents at the Union Carbide chemical factory in Bhopal, India in 1984 (a leak of methyl isocyanate caused thousands of deaths), and at the Sandoz chemical warehouse in Basel, Switzerland in 1986 (fire-fighting water contaminated with mercury, organophosphate pesticides and other chemicals caused massive pollution of the Rhine River and the death of hundreds of thousands of fish). Both amendments, broadened the scope of the Directive, in particular to include the storage of dangerous substances. 

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