5.27 A chemistry student accidentally drops a large mercury thermometer and it b
ID: 568619 • Letter: 5
Question
5.27 A chemistry student accidentally drops a large mercury thermometer and it breaks. The thermometer contained 2 g mercury (Hg), a potent neurotoxin. The Hg leaks out and pools a dro Occupational Safety and Health Administration (OSHA) sets the permissible exposure limit (PEL) for mercury vapor in air at 12 ppb, by volume. At no time should anyone be exposed to mercury vapor above this threshold. The molar mass of Hg is 201 g/mol. The temperature and pressure in the lab are 14.7 psia and 70°F respectively ls together into a droplet on the floor of the laboratory. The 212 a. Convert the Hg vapor PEL into mg/m3 b. A professor immediately evacuates the room and seals it off so that no air can flow in or out. The drop begins to evaporate from the drop into the air at a rate of 0.4 g/min. The laboratory (air) measures 100 m, within 45 min, a cleanup crew arrives. Has the mercury vapor concentration exceeded the PEL by this time? (We even distribution of the evaporated mercury throughout the lab.) assume an The cleanup crew has a cantilever mass sensor. The cantilever is coated in gold, which binds to mercury vapor. The cantilever is 655 m long, 10um wide, with a modulus of elasticity EM-100 GPa and density = 2330 kg/m3 and the minimum detectable frequency change Afmin0.1 Hz. What is the minimum detectable mass of this sensor? c. d. What is the minimum number of Hg molecules that must collect on the sensor to equal the minimum detectable mass? (Assume that only Hg collects on the sensor.) e. The sensor system is coupled to a pump that pulls in a 10-m sample of the contaminated air (after the 45 min of Hg evaporation). What is the minimum percentage of the mass of mercury in this sample that must be collected on the cantilever sensor to detect the mercury?
Explanation / Answer
It is HMC policy that when a spill occurs, the responsibility for having the spill cleaned up rests with the person causing the spill. If the individual responsible is or unable to clean up the spill for any reason, then responsibility for assessing the spill rests with the Department. Contact the Chemical Hygiene Officer for assistance.
If the spill is large, complicated, toxic, or fumy, and occurs outside of the fume hood, a hazardous materials team may be called in for assistance. Custodians are not permitted to clean up spills of hazardous materials.
Experiments should always be designed so as to minimize the possibility of an accidental release of hazardous substances. Plan your experiments to use the minimal amounts of hazardous compounds practical and alwaystransport such materials properly using break-resistant bottles or secondary containers.
As discussed further below, develop a contingency plan to handle spills when working with hazardous substances. In the event a spill does occur, the following General Guidelinesfor Handling Spills should be followed in the indicated order of priority. Tend to any injured or contaminated personnel and if necessary request help (Campus Safety x.72000).
Notify other personnel of the accident and if necessary evacuate the area. Use the buddy system when attending to a spill. Take steps to confine and limit the spill if this can be done without risk of injury or contamination. Prevent spill from entering sinks or drains. Clean up the spill using adsorbent and/or neutralizing materials.
Dispose of contaminated material properly as hazardous waste. Clean spill area with detergent and water. The following section outlines specific procedures for handling the accidental release of hazardous substances.
Mercury
The element mercury is a liquid metal with a vapor pressure of 0.00185 mm at 25oC. This corresponds to a saturation concentration of 20 mg of mercury per cubic meter of air or 2.4 ppm of air. The ACGIH has established a TLV for mercury vapor of 0.05 mg/m3 for continuous 40- hour per week exposure.
Long-term chronic exposure to mercury vapor in excess of 0.05 mg/m3 may result in cumulative poisoning. The use of mercury in laboratory amounts in well-ventilated areas is fairly safe; however special precautions must be followed when working with large quantities of mercury. Mercury poisoning from exposure by chronic inhalation produces a variety of symptoms. The characteristic effects are emotional disturbances, unsteadiness, inflammation of the mouth and gums, general fatigue, memory loss, and headaches. Kidney damage may result from poisoning by mercury salts.
In most cases of exposure by chronic inhalation, the symptoms of poisoning gradually disappear when the source of exposure is removed. However, improvement may be slow and complete recovery may take years. Skin contact with mercury produces irritation and various degrees of corrosion. Soluble mercury salts can be absorbed through the intact skin and produce poisoning.
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