Disclaimer: These guidelines were developed under contract using generally accepted secondary sources. The protocol used by the contractor for surveying these data sources was developed by the National Institute for Occupational Safety and Health (NIOSH), the Occupational Safety and Health Administration (OSHA), and the Department of Energy (DOE). The information contained in these guidelines is intended for reference purposes only. None of the agencies have conducted a comprehensive check of the information and data contained in these sources. It provides a summary of information about chemicals that workers may be exposed to in their workplaces. The secondary sources used for supplements 111 and 1V were published before 1992 and 1993, respectively, and for the remainder of the guidelines the secondary sources used were published before September 1996. This information may be superseded by new developments in the field of industrial hygiene. Therefore readers are advised to determine whether new information is available.

OCCUPATIONAL SAFETY AND HEALTH GUIDELINE FOR MERCURY VAPOR

INTRODUCTION

This guideline summarizes pertinent information about mercury vapor for workers and employers as well as for physicians, industrial hygienists, and other occupational safety and health professionals who may need such information to conduct effective occupational safety and health programs. Recommendations may be superseded by new developments in these fields; readers are therefore advised to regard these recommendations as general guidelines and to determine whether new information is available.

SUBSTANCE IDENTIFICATION

* Formula

Hg

* Structure

(For Structure, see paper copy)

* Synonyms

None reported.

* Identifiers

1. CAS No.: 7439-97-6

2. RTECS No.: OV4550000

3. Specific DOT number: None

4. Specific DOT label: None

* Appearance and odor

Mercury vapor is the vapor generated from elemental liquid mercury or compounds of mercury. No information is available on the appearance or odor of mercury vapor.

CHEMICAL AND PHYSICAL PROPERTIES

* Physical data

1. Atomic weight: 200.59

2. Boiling point: Not applicable.

3. Specific gravity: Not applicable.

4. Vapor density: Data not available.

5. Melting/Freezing point: Not applicable.

6. Vapor pressure: Not applicable.

7. Solubility: Not applicable.

8. Evaporation rate: Not applicable.

* Reactivity

1. Conditions contributing to instability: None reported.

2. Incompatibilities: None reported.

3. Hazardous decomposition products: Not applicable.

4. Special precautions: None reported.

* Flammability

The National Fire Protection Association has not assigned a flammability rating to mercury vapor.

1. Flash point: Not applicable.

2. Autoignition temperature: Not applicable.

3. Flammable limits in air: Not applicable.

4. Extinguishant: Use an extinguishant that is suitable for the materials involved in the surrounding fire.

Fires involving mercury vapor should be fought upwind from the maximum distance possible. Isolate the hazard area and deny access to unnecessary personnel. Firefighters should wear a full set of protective clothing and self-contained breathing apparatus when fighting fires involving mercury vapor.

EXPOSURE LIMITS

* OSHA PEL The current Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) for mercury vapor is 0.1 milligram per cubic meter (mg/m(3)) of air as a ceiling limit. A worker's exposure to mercury vapor shall at no time exceed this ceiling level.

* NIOSH REL

The National Institute for Occupational Safety and Health (NIOSH) has established a recommended exposure limit (REL) for mercury vapor of 0.05 mg/m(3) as a TWA for up to a 10-hour workday and a 40-hour workweek. NIOSH also assigns a "Skin" notation, which indicates that the cutaneous route of exposure, including mucous membranes and eyes, contributes to overall exposure [NIOSH 1992].

* ACGIH TLV

The American Conference of Governmental Industrial Hygienists (ACGIH) has assigned mercury vapor a threshold limit value (TLV) of 0.025 mg/m(3) as a TWA for a normal 8-hour workday and a 40-hour workweek and considers mercury vapor an A4 substance (not classifiable as a human carcinogen). The ACGIH also assigns a "Skin" notation to mercury vapor [ACGIH 1994, p. 25].

* Rationale for Limits

The NIOSH limit is based on the risk of central nervous system damage, eye, skin, and respiratory tract irritation [NIOSH 1992].

The ACGIH has not published documentation for the current TLV for mercury vapor. The 1991 Documentation of Threshold Limit Values (6th edition) discusses the basis for the prior TLV of 0.05 mg/m(3), but does not discuss the current TLV for mercury vapor [ACGIH 1991, p. 881].

HEALTH HAZARD INFORMATION

* Routes of Exposure

Exposure to mercury vapor can occur through inhalation, and eye or skin contact.

* Summary of toxicology

1. Effects on Animals: Mercury vapor can damage the kidneys, liver, brain, heart, lungs and colon in experimental animals. It is also mutagenic and can affect the immune system. Rabbits exposed for a single 4 hour period to mercury vapor at a concentration of 28.8 mg/m(3) developed severe damage to the kidneys, liver, brain, heart, lungs, and colon [Clayton and Clayton 1981]. Rabbits exposed to 0.86 mg/m(3) for 6 weeks had significant brain and kidney damage, which resolved on cessation of exposure. Exposure to 6 mg/m(3) mercury vapor caused severe damage to the kidney, heart, lung, and brain of rabbits; however, dogs exposed to 0.1 mg/m(3) for 83 weeks had no microscopic indication of tissue damage [Clayton and Clayton 1981]. Mercury may injure the kidneys through an autoimmune mechanism [ACGIH 1991]. Mercury was mutagenic in eukaryotic cells [ACGIH 1991].

2. Effects on Humans: Mercury vapor can cause effects in the central and peripheral nervous systems, lungs, kidneys, skin and eyes in humans. It is also mutagenic and affects the immune system [Hathaway et al. 1991; Clayton and Clayton 1981; Rom 1992]. Acute exposure to high concentrations of mercury vapor causes severe respiratory damage, while chronic exposure to lower levels is primarily associated with central nervous system damage [Hathaway et al. 1991]. Chronic exposure to mercury is also associated with behavioral changes and alterations in peripheral nervous system [ACGIH 1991]. Pulmonary effects of mercury vapor inhalation include diffuse interstitial pneumonitis with profuse fibrinous exudation [Gosselin 1984]. Glomerular dysfunction and proteinuria have been observed mercury exposed workers [ACGIH 1991]. Chronic mercury exposure can cause discoloration of the cornea and lens, eyelid tremor and, rarely, disturbances of vision and extraocular muscles [Grant 1986]. Delayed hypersensitivity reactions have been reported in individuals exposed to mercury vapor [Clayton and Clayton 1981]. Mercury vapor is reported to be mutagenic in humans, causing aneuploidy in lymphocytes of exposed workers [Hathaway et al. 1991].

* Signs and symptoms of exposure

1. Acute exposure: Acute inhalation of mercury vapor may result in toxicity similar to metal fume fever including chills, nausea, general malaise, tightness in the chest, chest pains, dyspnea, cough, stomatitis, gingivitis, salivation, and diarrhea [ACGIH 1991; Hathaway et al. 1991].

2. Chronic exposure: Chronic exposure to mercury may result in weakness, fatigue, anorexia, weight loss, and disturbance of gastrointestinal function. A tremor may develop beginning with the fingers, eyelids, and lips which may progress to generalized trembling of the entire body and violent chronic spasms of the extremities. Parallel with development of the tremors, behavioral and personality changes may develop including increased excitability, memory loss, insomnia, and depression. The skin may exhibit abnormal blushing, dermographia, excessive sweating and irregular macular rashes. Severe salivation and gingivitis is also characteristic of chronic toxicity [Hathaway et al. 1991; Gosselin 1984]. Another manifestation of chronic mercury exposure is characterized by apathy, anorexia, flush, fever, a nephrotic syndrome with albuminuria and generalized edema, diaphoresis, photophobia, insomnia and a pruritic and sometimes painful scaling or peeling of the skin of the hands and feet with bullous lesions [Gosselin 1984].

EMERGENCY MEDICAL PROCEDURES

* Emergency medical procedures: [NIOSH to supply]

5. Rescue: Remove an incapacitated worker from further exposure and implement appropriate emergency procedures (e.g., those listed on the Material Safety Data Sheet required by OSHA's Hazard Communication Standard [29 CFR 1910.1200]). All workers should be familiar with emergency procedures, the location and proper use of emergency equipment, and methods of protecting themselves during rescue operations.

EXPOSURE SOURCES AND CONTROL METHODS

The following operations may involve mercury and lead to worker exposures to the vapor of this substance:

* The mining, production, and transportation of mercury

* The mining and refining operations for gold and silver ores

* Use in thermometers, manometers, barometers, gauges, and valves

* Use in amalgams for dentistry, preservatives, heat transfer technology, pigments, catalysts, and in lubricating oils

Methods that are effective in controlling worker exposures to mercury vapor, depending on the feasibility of implementation, are as follows:

* Process enclosure
* Local exhaust ventilation
* General dilution ventilation
* Personal protective equipment

Workers responding to a release or potential release of a hazardous substance must be protected as required by paragraph (q) of OSHA's Hazardous Waste Operations and Emergency Response Standard [29 CFR 1910.120].

Good sources of information about control methods are as follows:

1. ACGIH [1992]. Industrial ventilation--a manual of recommended practice. 21st ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists.

2. Burton DJ [1986]. Industrial ventilation--a self study companion. Cincinnati, OH: American Conference of Governmental Industrial Hygienists.

3. Alden JL, Kane JM [1982]. Design of industrial ventilation systems. New York, NY: Industrial Press, Inc.

4. Wadden RA, Scheff PA [1987]. Engineering design for control of workplace hazards. New York, NY: McGraw-Hill.

5. Plog BA [1988]. Fundamentals of industrial hygiene. Chicago, IL: National Safety Council.

MEDICAL SURVEILLANCE

OSHA is currently developing requirements for medical surveillance. When these requirements are promulgated, readers should refer to them for additional information and to determine whether employers whose employees are exposed to mercury vapor are required to implement medical surveillance procedures.

* Medical Screening

Workers who may be exposed to chemical hazards should be monitored in a systematic program of medical surveillance that is intended to prevent occupational injury and disease. The program should include education of employers and workers about work-related hazards, early detection of adverse health effects, and referral of workers for diagnosis and treatment. The occurrence of disease or other work-related adverse health effects should prompt immediate evaluation of primary preventive measures (e.g., industrial hygiene monitoring, engineering controls, and personal protective equipment). A medical surveillance program is intended to supplement, not replace, such measures. To detect and control work-related health effects, medical evaluations should be performed (1) before job placement, (2) periodically during the term of employment, and (3) at the time of job transfer or termination.

* Preplacement medical evaluation

Before a worker is placed in a job with a potential for exposure to mercury vapor, a licensed health care professional should evaluate and document the worker's baseline health status with thorough medical, environmental, and occupational histories, a physical examination, and physiologic and laboratory tests appropriate for the anticipated occupational risks. These should concentrate on the function and integrity of the eyes, skin, respiratory system, central and peripheral nervous systems, and kidneys. Medical surveillance for respiratory disease should be conducted using the principles and methods recommended by the American Thoracic Society.

A preplacement medical evaluation is recommended to assess medical conditions that may be aggravated or may result in increased risk when a worker is exposed to mercury vapor at or below the prescribed exposure limit. The health care professional should consider the probable frequency, intensity, and duration of exposure as well as the nature and degree of any applicable medical condition. Such conditions (which should not be regarded as absolute contraindications to job placement) include a history and other findings consistent with diseases of the eyes, skin, respiratory system, central and peripheral nervous systems, or kidneys.

* Periodic medical evaluations

Occupational health interviews and physical examinations should be performed at regular intervals during the employment period, as mandated by any applicable Federal, State, or local standard. Where no standard exists and the hazard is minimal, evaluations should be conducted every 3 to 5 years or as frequently as recommended by an experienced occupational health physician. Additional examinations may be necessary if a worker develops symptoms attributable to mercury vapor exposure. The interviews, examinations, and medical screening tests should focus on identifying the adverse effects of mercury vapor on the eyes, skin, respiratory system, central and peripheral nervous systems, or kidneys. Current health status should be compared with the baseline health status of the individual worker or with expected values for a suitable reference population.

* Termination medical evaluations

The medical, environmental, and occupational history interviews, the physical examination, and selected physiologic or laboratory tests that were conducted at the time of placement should be repeated at the time of job transfer or termination to determine the worker's medical status at the end of his or her employment. Any changes in the worker's health status should be compared with those expected for a suitable reference population.

* Biological monitoring

Biological monitoring involves sampling and analyzing body tissues or fluids to provide an index of exposure to a toxic substance or metabolite. No biological monitoring test acceptable for routine use has yet been developed for mercury vapor. However, total inorganic mercury can be measured in the urine by preshift sampling. A mercury level of 35 micrograms per gram of creatinine should be used as the biological exposure index. In addition, total inorganic mercury can also be measured in the blood by sampling at the end of shift at the end of the workweek. A mercury level of 15 micrograms per liter of blood should be used as the biological exposure index.

WORKPLACE MONITORING AND MEASUREMENT

Determination of a worker's exposure to airborne mercury vapor is made using a Hydrar or Hopcalite tube (200 mg section), SKC brand with a prefilter/cassette. Samples are collected at a maximum flow rate of 0.2 liter/minute (TWA) until a minimum collection volume of 3 liters (or a maximum collection volume of 96 liters) is reached. Analysis is conducted by atomic absorption spectroscopy/ cold vapor (AAS/cold vapor). This method (OSHA ID-140) is described in the OSHA Computerized Information System [OSHA 1994] and is fully validated. This method is also described in NIOSH Method No. 6009 of the NIOSH Manual of Analytical Methods [NIOSH 1994b].

SPECIAL REQUIREMENTS

U.S. Environmental Protection Agency (EPA) requirements for emergency planning, reportable quantities of hazardous releases, community right-to-know, and hazardous waste management may change over time. Users are therefore advised to determine periodically whether new information is available. The following section uses information pertaining to elemental mercury because mercury vapor itself is not listed.

* Emergency planning requirements

Mercury is not subject to EPA emergency planning requirements under the Superfund Amendments and Reauthorization Act (SARA) (Title III) in 42 USC 11022.

* Reportable quantity requirements for hazardous releases

A hazardous substance release is defined by EPA as any spilling, leaking, pumping, pouring, emitting, emptying, discharging, injecting, escaping, leaching, dumping, or disposing into the environment (including the abandonment or discarding of contaminated containers) of hazardous substances. In the event of a release that is above the reportable quantity for that chemical, employers are required to notify the proper Federal, State, and local authorities [40 CFR 355.40].

The reportable quantity of mercury is 1 pound. If an amount equal to or greater than this quantity is released within a 24-hour period in a manner that will expose persons outside the facility, employers are required to do the following:

- Notify the National Response Center immediately at (800) 424-8802 or at (202) 426-2675 in Washington, D.C. [40 CFR 302.6].

* Community right-to-know requirements

Employers who own or operate facilities in SIC codes 20 to 39 that employ 10 or more workers and that manufacture 25,000 pounds or more of mercury per calendar year or otherwise use 10,000 pounds or more of mercury per calendar year are required by EPA [40 CFR Part 372.30] to submit a Toxic Chemical Release Inventory form (Form R) to EPA reporting the amount of mercury emitted or released from their facility annually.

* Hazardous waste management requirements

EPA considers a waste to be hazardous if it exhibits any of the following characteristics: ignitability, corrosivity, reactivity, or toxicity as defined in 40 CFR 261.21-261.24. Under the Resource Conservation and Recovery Act (RCRA) [40 USC 6901 et seq.], EPA has specifically listed many chemical wastes as hazardous. Mercury is listed as a hazardous waste under RCRA and has been assigned EPA Hazardous Waste No. U151. This substance has been banned from land disposal until treated by retorting or roasting.

Providing detailed information about the removal and disposal of specific chemicals is beyond the scope of this guideline. The U.S. Department of Transportation, EPA, and State and local regulations should be followed to ensure that removal, transport, and disposal of this substance are conducted in accordance with existing regulations. To be certain that chemical waste disposal meets EPA regulatory requirements, employers should address any questions to the RCRA hotline at (703) 412-9810 (in the Washington, D.C. area) or toll-free at (800) 424-9346 (outside Washington, D.C.). In addition, relevant State and local authorities should be contacted for information on any requirements they may have for the waste removal and disposal of this substance.

RESPIRATORY PROTECTION

* Conditions for respirator use

Good industrial hygiene practice requires that engineering controls be used where feasible to reduce workplace concentrations of hazardous materials to the prescribed exposure limit. However, some situations may require the use of respirators to control exposure. Respirators must be worn if the ambient concentration of mercury vapor exceeds prescribed exposure limits. Respirators may be used (1) before engineering controls have been installed, (2) during work operations such as maintenance or repair activities that involve unknown exposures, (3) during operations that require entry into tanks or closed vessels, and (4) during emergencies. Workers should only use respirators that have been approved by NIOSH and the Mine Safety and Health Administration (MSHA).

* Respiratory protection program

Employers should institute a complete respiratory protection program that, at a minimum, complies with the requirements of OSHA's Respiratory Protection Standard [29 CFR 1910.134]. Such a program must include respirator selection, an evaluation of the worker's ability to perform the work while wearing a respirator, the regular training of personnel, respirator fit testing, periodic workplace monitoring, and regular respirator maintenance, inspection, and cleaning. The implementation of an adequate respiratory protection program (including selection of the correct respirator) requires that a knowledgeable person be in charge of the program and that the program be evaluated regularly. For additional information on the selection and use of respirators and on the medical screening of respirator users, consult the latest edition of the NIOSH Respirator Decision Logic [NIOSH 1987b] and the NIOSH Guide to Industrial Respiratory Protection [NIOSH 1987a].

PERSONAL PROTECTIVE EQUIPMENT

Workers should use appropriate personal protective clothing and equipment that must be carefully selected, used, and maintained to be effective in preventing skin contact with mercury vapor. The selection of the appropriate personal protective equipment (PPE) (e.g., gloves, sleeves, encapsulating suits) should be based on the extent of the worker's potential exposure to mercury vapor. There are no published reports on the resistance of various materials to permeation by mercury vapor.

To evaluate the use of PPE materials with mercury vapor, users should consult the best available performance data and manufacturers' recommendations. Significant differences have been demonstrated in the chemical resistance of generically similar PPE materials (e.g., butyl) produced by different manufacturers. In addition, the chemical resistance of a mixture may be significantly different from that of any of its neat components.

Any chemical-resistant clothing that is used should be periodically evaluated to determine its effectiveness in preventing dermal contact. Safety showers and eye wash stations should be located close to operations that involve mercury vapor.

Splash-proof chemical safety goggles or face shields (20 to 30 cm long, minimum) should be worn during any operation in which a solvent, caustic, or other toxic substance may be splashed into the eyes.

In addition to the possible need for wearing protective outer apparel (e.g., aprons, encapsulating suits), workers should wear work uniforms, coveralls, or similar full-body coverings that are laundered each day. Employers should provide lockers or other closed areas to store work and street clothing separately. Employers should collect work clothing at the end of each work shift and provide for its laundering. Laundry personnel should be informed about the potential hazards of handling contaminated clothing and instructed about measures to minimize their health risk.

Protective clothing should be kept free of oil and grease and should be inspected and maintained regularly to preserve its effectiveness.

Protective clothing may interfere with the body's heat dissipation, especially during hot weather or during work in hot or poorly ventilated work environments.

REFERENCES

ACGIH [1991]. Documentation of the threshold limit values and biological exposure indices. 6th ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists.

ACGIH [1994]. 1994-1995 Threshold limit values for chemical substances and physical agents and biological exposure indices. Cincinnati, OH: American Conference of Governmental Industrial Hygienists.

ATS [1987]. Standardization of spirometry -- 1987 update. American Thoracic Society. Am Rev Respir Dis 136:1285-1296.

CFR. Code of Federal regulations. Washington, DC: U.S. Government Printing Office, Office of the Federal Register.

Clayton G, Clayton F [1981-1982]. Patty's industrial hygiene and toxicology. 3rd rev. ed. New York, NY: John Wiley & Sons.

Gosselin RE, Smith RP, Hodge HC [1984]. Clinical toxicology of commercial products. 5th ed. Baltimore, MD: Williams & Wilkins.

Grant WM [1986]. Toxicology of the eye. 3rd ed. Springfield, IL: Charles C Thomas.

Hathaway GJ, Proctor NH, Hughes JP, and Fischman ML [1991]. Proctor and Hughes' chemical hazards of the workplace. 3rd ed. New York, NY: Van Nostrand Reinhold.

Mickelsen RL, Hall RC [1987]. A breakthrough time comparison of nitrile and neoprene glove materials produced by different glove manufacturers. Am Ind Hyg Assoc J 48(11): 941-947.

Mickelsen RL, Hall RC, Chern RT, Myers JR [1991]. Evaluation of a simple weight-loss method for determining the permeation of organic liquids through rubber films. Am Ind Hyg Assoc J 52(10): 445-447.

NIOSH [1987a]. NIOSH guide to industrial respiratory protection. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 87-116.

NIOSH [1987b]. NIOSH respirator decision logic. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 87-108.

NIOSH [1992]. Recommendations for occupational safety and health: Compendium of policy documents and statements. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 92-100.

NIOSH [1994a]. NIOSH pocket guide to chemical hazards. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 94-116.

NIOSH [1994b]. NIOSH manual of analytical methods. 4th ed. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 94-113.

NIOSH [1995]. Registry of toxic effects of chemical substances: Mercury. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, Division of Standards Development and Technology Transfer, Technical Information Branch.

NLM [1995]. Hazardous substances data bank: Mercury. Bethesda, MD: National Library of Medicine.

OSHA [1994]. Computerized information system. Washington, DC: U.S. Department of Labor, Occupational Safety and Health Administration.

Rom WN [1992]. Environmental and occupational medicine. 2nd ed. Boston, MA: Little, Brown and Company.

USC. United States code. Washington. DC: U.S. Government Printing Office.

Windholz M, ed. [1983]. Merck Index 10th ed. Rahway, NJ: Merck & Company.