Medical/Measuring Devices

Barometers and Vacuum Gauges

Use: Barometers are used to measure atmospheric pressure.

Description: Mercury-containing barometers are typically long cylindrical tubes filled with mercury where the atmosperhic pressure displaces the mercury in the tube. They are still commonly used in schools, households and for airport, weather monitoring and farming applications. Gauges containing mercury have been designed for various applications in which the measurement of pressure is required. Historically, mercury has been used because it responds precisely to air pressure. Manometers, U-shaped tubes that can be filled with mercury, measure pressure differences. Mercury barometers, which are straight tubes filled and inverted into a dish of mercury, measure air pressure.

Identification: Mercury containing pressure gauges, which can be found in many settings, can be identified by the presence of a tube containing silver liquid in an instrument used to measure pressure. Weather barometers are used to determine atmospheric pressure. There are various types of mercury barometers available for home, commerical, and laboratory uses. For example, Barometers may contain a large volume of mercury held in a reservoir. Collectable antiques are often mounted on a decorative wooden plaque or on a highly polished metal mounting. Laboratory and commercial barometer units are less decorative and built for functionality.

Mercury Content: Mercury content generally ranges from 300 to 600 grams. Rare old collectable barometers have been found to contain as much as 6 kilograms (P.Collins, Barometer World Ltd, 2003, personal communication).

Alternatives: Aneroid and digital options are usually available. Electronic programmable and digital barometers are also considered to be accurate as the mercury barometer (Galligan et al., 2002).

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Flame Sensors

Use: Mercury flame sensors were used in older gas-fired appliances (e.g. dryers, stoves, and furnances) to open or shut off gas. Another type of flame sensor is used in fire detection systems that are sued to activate sprinkler systems or alarms.

Description: Some older gas-fired appliances may contain mercury flame sensors. A flame sensor consists of a metal bulb and a thin tube attached to a gas-control valve. There is mercury inside the tube and it expands or contracts to open or shut off the gas valve (G&S Mechanical Services, 2003).

Identification: Gas-shut-off flame sensors can usually be identified by a slender, lengthy piece of copper tubing, with one end fitted with a coupling to screw into an appliance and the other end sealed with a slighter larger piece of tubing that contains the mercury (G&S Mechanical Services, 2003).

Mercury content: Sensors contain about 1 gram of mercury.

Alternatives: Due to high cost, retrofitting an appliance with an electric ignition pilot is not recommended unless the appliance is already wired with electricity. However, most new appliances have been manufactured with non-mercury flame sensors (Purdue University, 2003). Old appliances can be replaced with either an appliance with an electric ignition or an electrical appliance.

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Use: Flowmeters measure the rate of flow of gas, water, air and streams.

Description: Flowmeters are used in water and sewage treatment plants, power stations, and many other industrial applications. Mercury-containing flowmeters are generally no longer manufactured and have been replaced by electronic or digital units (Galligan et al., 2002).

Identification: Flowmeters can be described as having manometers attached to an assembly for the measurement of the rate of flow of a liquid or gaseous substance.

Mercury content: Flowmeters can contain up to 5000 grams of mercury (Purdue University, 2003).

Alternatives: Digital and electronic instrumentation may replace most manometers used in flowmeters. The price range varies depending on the application.


Use: Hydrometers measure the specific gravity and density of a liquid.

Description: Hydrometers are most commonly used in laboratories, the petroleum and dairy industries and in the production of alcohol.

Identification: Hydrometers have a long stem of mercury in a glass tube, similar to a laboratory thermometer, except that the bulb at the bottom of the hydrometer is wider and weighted to keep the hydrometer upright when placed in a liquid.

Mercury content: Content can range from 0.002 grams to 1 gram depending on the application and size of instrument.

Alternatives: Alternatives to mercury-containing hydrometers are alcohol-filled, digital, and aneroid hydrometers (NEWMOA, 2003). Alcohol-filled and mercury-filled hydrometers are equally reliable in measuring specific gravity.


Use: Hygrometers measure the moisture content in air. A psychrometer is the most common type of hygrometer.

Description: Psychrometers are best described as dual thermometers, one with a wet base and the other with a dry base. Moisture from the wet base evaporates and absorbs heat causing the thermometer reading to drop. Relative humidity is calculated from he difference between the wet-and dry-base thermometers using a conversion table (Galligan et al., 2002). Although not common in most workplaces, hygrometers/psychrometers are found in workplaces where ambient moisture measurements are used for predicting weather and atmospheric conditions.

Identification: Hygrometers look like industrial thermometers with the distinct attachment of a cotton bulb. Sling psychrometers are designed to be twirled in the air to measure ambient moisture.

Mercury content: Content generally ranges from 3 to 7 grams.

Alternatives: Alternatives include alcohol-filled and digital instruments. Both alternatives are equally reliable to mercury-containing prodcuts. In fact, the digital hygrometers can be more accurate if properly calibrated because human error is eliminated (Galligan et al., 2002).


Use: Manometers are used to measure air, water and gas pressure. Those containing mercury are almost exclusively used to measure gas pressures. They are used also as primary pressure standards in laboratories, meteorology and industry, and to calibrate secondary pressure measuing instruments like electronic and aneroid gauges.

Description: A mercury manometer consists of a vertical tube (usually made of glass) containing liquid mercury. Gas pressure is pushed up the column of mercury in the tube and the height of the mercury column indicates the pressure relative to the reference.

Identification: Laboratory manometers range from bench-and wall-mounted units to larger self-supporting encased apparatuses. Dairy manometers are commonly found in dairy barns hooked to automated milking equipment.

Mercury content: Milking system manometers contain approximately 340 grams of mercury (State of Ohio EPA, 2001). Other manometers may contain from 100 to 500 grams or more (Purdue University, 2003).

Alternatives: Alternatives to manometers include devices that use a non-mercury liquid, needle bourdon gauges, aneroid manometers, and digital manometers. Digital manometers can be more accurate than mercury manometers if properly calibrated.

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Use: Pyrometers are used to measure extremely hot materials in foundry applications and exhaust temperatures for large engines (Galligan et al., 2002).

Description: Mercury is the medium used in the stem of mercurial pyrometers.

Identification: The typical mercurial pyrometer is equipped with a dial gauge and temperature-sensing stem. It is difficult to tell the difference between mercury and non-mercury alternatives. Mercurial pyrometers are becoming obsolete as nitrogen probes or digital instruments are replacing them.

Mercury content: Content ranges from 5 to 10 grams. Verify with manufacturer specifications for actual content.

Alternatives: Alternatives available to mercurial pyrometers include nitrogen containing stem and digital instruments. Costs of alternative products depend on model, stem length, attachments and certificate of calibration.

Thermostat Probes

Description: Thermostat probes or flame sensors found in gas appliances consist of a bulb attached to a gas-control valve by a tube containing mercury. They are generally used to prevent gas from flowing when the pilot light of the appliance is off.

Identification: Gas-fired appliances with pilot lights like stoves, clothes dryers, space heaters, water heaters and furnaces may have mercury-containing thermostat probes.

Mercury Content: Thermostat probes contain approximately 1 gram of mercury.

Alternatives: Electric flame sensors can be used instead of mercury-containing probes.

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Medical Devices

Medical devices are commonly used in the medical field. Some of these medical devices include esophageal dilators, gastrointestinal tubes and sphygmomanometers, which are fully described below. Exposure to mercury is the result of surgery practices, mercury spills when measuring high blood pressure and from extractions of intestinal obstructions. It is important to ensure that mercury-containing medical devices are used safely, effectively and are properly labelled. Of course, the best method of practice is to ensure staff and patients are aware of the hazards of using these medical devices and to avoid using high mercury-containing medical devices as much as possible.

Many medical devices that were commonly used years ago are slowly being phased out due to their potential harm to patients and potential for liabilities. Alternatives for practicioners are becoming standard in the medical field, are dropping in price and many devices are easier to use.

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Esophageal Dilators

Use: Esophageal dilators are used only in the medical field: they are used to dilate the esophagus of a patient during thoracic surgery, otolaryngology, and other medical procedures (University of Michigan, 2003). Mercury-filled dilators are becoming rare.

Description: Mercurial devices take advantage of the weight characteristics of mercury. The device is slipped down a patient's throat into the esophagus past the narrowed section.

Identification: The dilator is two tubes in one. The space between the outer and inner tubes houses the medium, typically mercury.

Mercury content: Esophageal dilators may contain more than 1000 grams of mercury (Sustainable Hospitals Project, 2003).

Alternatives: Mercury-containing dilators should be replaced immediately, because they have been known to rupture during handling causing undue harm to human health and the environment (Galligan et al., 2002). Water- and tungsten-filled dilators are common alternatives to mercury-containing esophageal dilators. The tungsten-filled dilator requires no retraining for medical practitioners (University of Michigan, 2003). Dilators have an expiration date, because the outer rubber casing degrades with time.

Gastrointestinal Tubes

Use: Gastrointestinal, Blakemore, and cantor tubes are used in the extraction of intestinal obstructions. Gastrointestinal tubes are only found in the medical field. Research suggests that these devices are no longer widely used (Galligan et al., 2002).

Description: Mercurial devices use mercury as a weight to guide the tube into place by gravity.

Identification: The gastrointestinal tube consists of an internal tube to allow the passage of air; and a larger outer tube into which mercury or an alternate substance is poured for weight.

Mercury content: These devices may contain approximately 1000 grams when filled to capacity.

Alternatives: An alternative for mercury gastrointestinal tubes is tungsten-weighted tubes.


Use: Sphygmomanometers are manometers used to measure human blood pressure. Mercurial sphygmomanometers have been the standard in the medical field for many years but are being phased out and replaced with aneroid and digital products due to liability associated with mercury spills.

Description: A mercury sphygmomanometer is a mercury manometer connected to a bladder cuff that wraps around a patient's arm. A vertical glass tube containing mercury indicates the cuff pressure while the person taking the pressure listens for arterial sounds in the patient's arm with a stethoscope.

Identification: The device typically uses a bladder cuff that wraps around a patient?s arm. Two hoses come off the cuff: one to a bulb/pump for pumping air pressure, and the other to the mercurial device that measures the actual pressure.

Mercury content: Content can vary from 20 to 60 grams of mercury.

Alternatives: Alternatives to mercurial sphygmomanometers are aneroid and digital products. Both are reliable, accepted as standard, and comparable to mercurial sphygmomanometers. Digital products continue to drop in price and are easiest to use.

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