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 This information may be superseded by new developments in the field of industrial hygiene.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 HAFNIUM

INTRODUCTION

This guideline summarizes pertinent information about hafnium 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 Recommendations may be superseded by new developments in these fields; readers are therefore advised to regard these recommendations as general guidelines and to determine whether new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

Hf

* Structure

(For Structure, see paper copy)

* Synonyms

Metallic hafnium, elemental hafnium, celtium

* Identifiers

1. CAS No.: 7440-58-6

2. RTECS No.: MG4600000

3. DOT UN: 1326 32 (wetted); 2545 40 (dry)

4. DOT label: Spontaneously Combustible (dry); Flammable solid (wetted)

* Appearance and odor

Hafnium is an odorless, metallic element with the atomic number 72; it has six stable isotopes. It is a hard, shiny, ductile metal that is available commercially as powder, rods, or single crystals.

CHEMICAL AND PHYSICAL PROPERTIES

* Physical data

1. Molecular weight: 178.5

2. Boiling point (at 760 mm Hg): 4602 degrees C (8315 degrees F)

3. Specific gravity (water = 1): 13.3 at 20 degrees C (68 degrees F)

4. Vapor density: Not applicable.

5. Melting point: 2227 degrees C (4040 degrees F)

6. Vapor pressure: Data not available.

7. Solubility: Insoluble in water, soluble in hydrogen fluoride.

8. Evaporation rate: Not applicable.

* Reactivity

1. Conditions contributing to instability: None reported.

2. Incompatibilities: Contact between powdered hafnium metal and chlorine, nonmetals, hot nitric acid, or strong oxidizers should be avoided. Finely divided hafnium is pyrophoric and can ignite spontaneously.

3. Hazardous decomposition products: Toxic gases and vapors (such as hydrogen chloride and carbon monoxide) may be released in a fire involving hafnium, hafnium tetrachloride, or hafnium oxychloride.

4. Special precautions: None reported.

* Flammability

The National Fire Protection Association has not assigned a flammability rating to hafnium. Other sources rate hafnium's fire hazard as severe when this substance is in dry powdered or wettable powder (less than 25 percent water) form and is exposed to heat or open flame.

1. Flash point: Data not available.

2. Autoignition temperature: 20 degrees C (68 degrees F) for dust cloud of powdered hafnium

3. Flammable limits in air: Data not available.

4. Extinguishant: For small fires use dry chemical, sand, earth, water spray, or regular foam. Use water spray, fog, or regular foam to fight large fires involving hafnium.

Fires involving hafnium should be fought upwind from the maximum distance possible. Keep unnecessary people away; isolate the hazard area and deny entry. For a massive fire in a cargo area, use unmanned hose holders or monitor nozzles; if this is impossible, withdraw from the area and let the fire burn. Emergency personnel should stay out of low areas and ventilate closed spaces before entering. May burn rapidly with a flare-burning effect. Containers of hafnium may explode in the heat of the fire and should be moved from the fire area if it is possible to do so safely. If this is not possible, cool fire exposed containers from the sides with water until well after the fire is out. Stay away from the ends of containers. Firefighters should wear a full set of protective clothing and self-contained breathing apparatus when fighting fires involving hafnium.

EXPOSURE LIMITS

* OSHA PEL

The current Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) for hafnium is 0.5 milligrams per cubic meter (mg/m(3)) of air as an 8-hour time-weighted average (TWA) concentration [29 CFR 1910.1000, Table Z-1].

* NIOSH REL

The National Institute for Occupational Safety and Health (NIOSH) has established a recommended exposure limit (REL) for hafnium of 0.5 mg/m(3) as a TWA for up to a 10-hour workday and a 40-hour workweek [NIOSH 1992].

* ACGIH TLV

The American Conference of Governmental Industrial Hygienists (ACGIH) has assigned hafnium a threshold limit value (TLV) of 0.5 mg/m(3) as a TWA for a normal 8-hour workday and a 40-hour workweek [ACGIH 1994, p. 22].

* Rationale for Limits

The NIOSH limit is based on the risk of liver damage, and eye and skin irritation in animals [NIOSH 1992].

The ACGIH limit is based on effects seen in animals [ACGIH 1991, p. 719].

HEALTH HAZARD INFORMATION

* Routes of Exposure

Exposure to hafnium can occur through inhalation, ingestion, and eye or skin contact [Sittig 1991, p. 864].

* Summary of toxicology

1. Effects on Animals: Data on the toxicity of hafnium metal or its dust are scant. Animal studies indicate that hafnium compounds cause eye, skin, and mucous membrane irritation, and liver damage [Hathaway et al. 1991]. The oral LD(50) for hafnium tetrachloride in rats is 2,362 mg/kg, and the intraperitoneal LD(50) in mice for hafnium oxychloride is 112 mg/kg [Sax and Lewis 1989]. Hafnium oxychloride was moderately to highly toxic when administered intraperitoneally or orally to mice [ACGIH 1991]. In cats, intravenous administration of hafnyl chloride at 10 mg/kg was fatal [ACGIH 1991; Hathaway et al. 1991]. Rats fed hafnium oxychloride or hafnium tetrachloride at the 1 ppm or 0.1 ppm level, respectively, for 90 days displayed perinuclear vacuolization of the parenchymal cells of the liver [Hathaway et al. 1991; ACGIH 1991]. Instillation of 1 mg of hafnium chloride into the eyes of rabbits caused eye blinking and hyperemia but no permanent injury [Grant 1986]. Topical application of hafnium chloride to the abraded skin of rabbits causes ulceration, and application to the unabraded skin causes transient edema and reddening [Hathaway et al. 1991].

2. Effects on Humans: Hafnium and its compounds are mild irritants of the eyes, skin, and mucous membranes [Hathaway et al. 1991]. No industrial poisonings involving hafnium have been reported [Hathaway et al. 1991].

* Signs and symptoms of exposure

1. Acute exposure: Overexposure to hafnium and its compounds may cause mild irritation of the eyes, skin, and mucous membranes.

2. Chronic exposure: No signs and symptoms of chronic exposure to hafnium have been reported in humans.

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 hafnium and lead to worker exposures to this substance:

* The manufacture and transportation of hafnium

* Liberated during the mining and purification of hafnium (separation from zirconium) and during the manufacture and fabrication of high-temperature alloys

* Use in control rods in water-cooled nuclear reactors; in gas-filled tubes and incandescent lamps as a scavenger for oxygen and nitrogen; in the manufacture of photographic flash bulbs, light bulb filaments, and in electronic equipment as cathodes and capacitors

* Use as a substitute for tantalum in cemented carbide tool bits, as a coating on rocket engine parts, and in radio and television tubes, and in X-ray tubes

Methods that are effective in controlling worker exposures to hafnium, 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 hafnium 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 hafnium, 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, and mucous membranes.

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 hafnium 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, and mucous membranes.

* 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 hafnium exposure. The interviews, examinations, and medical screening tests should focus on identifying the adverse effects of hafnium on the eyes, skin, or mucous membranes. 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 hafnium.

WORKPLACE MONITORING AND MEASUREMENT

Determination of a worker's exposure to airborne hafnium is made using a mixed cellulose ester filter (MCEF) 0.8 microns. Samples are collected at a maximum flow rate of 2 liters/minute until a minimum collection volume of 480 liters (maximum volume 960 liters) is reached. Analysis is conducted by atomic absorption spectroscopy (AAS). This method is not validated and is described in the OSHA Computerized Information System.

PERSONAL HYGIENE PROCEDURES

If hafnium contacts the skin, workers should flush the affected areas immediately with plenty of water, followed by washing with soap and water.

Clothing contaminated with hafnium should be removed immediately, and provisions should be made for the safe removal of the chemical from the clothing. Persons laundering the clothes should be informed of the hazardous properties of hafnium.

A worker who handles hafnium should thoroughly wash hands, forearms, and face with soap and water before eating, using tobacco products, using toilet facilities, applying cosmetics, or taking medication.

Workers should not eat, drink, use tobacco products, apply cosmetics, or take medication in areas where hafnium or a solution containing hafnium is handled, processed, or stored.

STORAGE

Hafnium should be stored in a cool, dry, well-ventilated area in tightly sealed containers that are labeled in accordance with OSHA's Hazard Communication Standard [29 CFR 1910.1200]. Containers of hafnium should be protected from physical damage, ignition sources, and should be stored separately from chlorine, nonmetals, hot nitric acid, strong oxidizers.

SPILLS AND LEAKS

In the event of a spill or leak involving hafnium, persons not wearing protective equipment and clothing should be restricted from contaminated areas until cleanup has been completed. The following steps should be undertaken following a spill or leak:

1. Notify safety personnel.

2. Remove all sources of heat and ignition.

3. For dry powdered hafnium spills, do not get water on the spilled material.

4. For small dry spills, use a clean shovel and place the material into a clean, dry container; cover and remove the container from the spill area.

5. For small liquid spills, take up with sand or other noncombustible absorbent material and place into closed containers for later disposal.

6. For large liquid spills, build dikes far ahead of the spill to contain the hafnium for later reclamation or disposal.

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.

* Emergency planning requirements

Hafnium 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].

Employers are not required by the emergency release notification provisions in 40 CFR Part 355.40 to notify the National Response Center of an accidental release of hafnium; there is no reportable quantity for this substance.

* Community right-to-know requirements

Employers are not required by EPA in 40 CFR Part 372.30 to submit a Toxic Chemical Release Inventory form (Form R) to EPA reporting the amount of hafnium 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. Although hafnium is not specifically listed as a hazardous waste under RCRA, EPA requires employers to treat waste as hazardous if it exhibits any of the characteristics discussed above.

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 hafnium 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 hafnium. 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 hafnium. There are no published reports on the resistance of various materials to permeation by hafnium.

To evaluate the use of PPE materials with hafnium, 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 hafnium.

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.

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DOT [1993]. 1993 Emergency response guidebook, guide 32, 40. Washington, DC: U.S. Department of Transportation, Office of Hazardous Materials Transportation, Research and Special Programs Administration.

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

Grayson M [1985]. Kirk-Othmer concise encyclopedia of chemical technology. Abridged version, 3rd ed. New York, NY: John Wiley & Sons.

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.

Lewis RJ, ed. [1993]. Hawley's condensed chemical dictionary. 12th ed. New York, NY: Van Nostrand Reinhold Company.

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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 [1991]. Registry of toxic effects of chemical substances: Hafnium. 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.

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 [1994]. 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.

NLM [1992]. Hazardous substances data bank: Hafnium. Bethesda, MD: National Library of Medicine.

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

Parmeggiani L [1983]. Encyclopedia of occupational health and safety. 3rd rev. ed. Geneva, Switzerland: International Labour Organisation.

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