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 This information may be superseded by new developments in the field of industrial hygiene.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

INTRODUCTION

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 Recommendations may be superseded by new developments in these fields; readers are therefore advised to regard these recommendations as general guidelines and to determine whether new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

B(2)H(6)

* Structure

(For Structure, see paper copy)

* Synonyms

Boroethane, boron hydride, diboron hexahydride

* Identifiers

1. CAS No.: 19287-45-7

2. RTECS No.: HQ9275000

3. DOT UN: 1911 18

4. DOT label: Flammable Gas, Poison Gas

* Appearance and odor

Diborane is a colorless gas with a repulsive, sweet odor. It is sometimes shipped as a liquid pressurized refrigerant. An air odor threshold of 2.5 parts per million (ppm) parts of air has been reported.

CHEMICAL AND PHYSICAL PROPERTIES

* Physical data

1. Molecular weight: 27.7

2. Boiling point (at 760 mm Hg): -92.5 degrees C (-134.5 degrees F)

3. Specific gravity (water = 1): 0.21 at 15 degrees C (59 degrees F)

4. Vapor density (air = 1): 0.96

5. Melting point: -165 degrees C (-265 degrees F)

6. Vapor pressure at 20 degrees C (68 degrees F): Greater than 760 mm Hg

7. Solubility: Ignites spontaneously in moist air or in contact with water and decomposes rapidly to form hydrogen gas; soluble in concentrated sulfuric acid, ammonium hydroxide, and carbon disulfide.

8. Evaporation rate: Not applicable.

* Reactivity

1. Conditions contributing to instability: Temperatures above -18 degrees C (-O.4 degrees F). Ignites spontaneously in moist air at room temperature.

2. Incompatibilities: Contact between diborane and air or halogenated compounds will cause fires and explosions. Reacts with water to form hydrogen and boric acid. Contact with aluminum, lithium, and other active metals forms hydrides that may ignite spontaneously. Diborane reacts with many oxidized surfaces as a strong reducing agent.

3. Hazardous decomposition products: Toxic gases and vapors such as hydrogen gas and boron oxide smoke may be released in a fire involving diborane.

4. Special precautions: Diborane will attack some forms of plastics, rubber, and coatings.

* Flammability

The National Fire Protection Association has assigned a flammability rating of 4 (extreme fire hazard) to diborane.

1. Flash point: Not applicable (gas).

2. Autoignition temperature: 38 to 52 degrees C (100 to 125 degrees F)

3. Flammable limits in air (percent by volume): Lower, 0.8; upper, 88.

4. Extinguishant: Let small fires burn unless leak can be stopped immediately. Use water spray, fog, or regular foam to fight large fires involving diborane. Caution should be taken when using water because violent reactions may result.

Fires involving diborane should be fought upwind from the maximum distance possible. Keep unnecessary people away; isolate the hazard area and deny entry. Isolate the area for 1/2 mile in all directions if a tank, rail car, or tank truck is involved in the fire. 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. Vapors may travel to a source of ignition and flash back. Vapors are an explosion and poison hazard indoors, outdoors, or in sewers. Containers of diborane 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. Personnel should withdraw immediately if a rising sound from a venting safety device is heard or if there is discoloration of a container due to fire. Firefighters should wear a full set of protective clothing and self-contained breathing apparatus when fighting fires involving diborane.

EXPOSURE LIMITS

* OSHA PEL

The current Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) for diborane is 0.1 ppm (0.1 milligrams per cubic meter (mg/m(3))) 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 diborane of 0.1 ppm (0.1 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 diborane a threshold limit value (TLV) of 0.1 ppm (0.11 mg/m(3)) as a TWA for a normal 8-hour workday and a 40-hour workweek [ACGIH 1994, p. 18].

* Rationale for Limits

The NIOSH limit is based on the risk of pulmonary irritation; liver and kidney damage in animals [NIOSH 1992].

The ACGIH limit is based on the risk of acute poisoning of the lungs and cumulative effects of the nervous system [ACGIH 1991, p. 393].

HEALTH HAZARD INFORMATION

* Routes of Exposure

Exposure to diborane can occur through inhalation and eye or skin contact [Sittig 1991].

* Summary of toxicology

1. Effects on Animals: Diborane is a respiratory irritant; it causes pulmonary edema and central nervous system intoxication in experimental animals [ACGIH 1991]. The inhalation 4-hour LC(50) in rats is about 50 ppm (40 mg/m(3)); the corresponding LC(50) for mice is 30 ppm. Seventeen of 18 rats exposed to 7 ppm diborane for six hours/day for 6 months died at intervals ranging from the 7th to the 113th exposure; dogs exposed on the same regimen began to die after the 10th exposure. When exposures were reduced to between 1 and 2 ppm, some dogs survived for 6 months. Mortality in both rats and dogs was attributed to respiratory complications resulting from repeated exposure [ACGIH 1991]. In other animal studies, acute exposure caused pulmonary edema, hemorrhage, and temporary damage to the liver and kidneys [Hathaway et al. 1991].

2. Effects on Humans: Diborane is primarily an irritant of the respiratory tract. Over exposure to diborane causes symptoms and signs similar to those seen in metal fume fever. Observations over a 5-year period involving 26 cases of acute diborane poisoning and 33 subacute episodes showed that the predominant effects of diborane poisoning are bronchopulmonary. Two cases of pneumonitis occurred, and one case of chronic respiratory distress [Clayton and Clayton 1982]. In chronic exposure, an increase in non-protein blood nitrogen and cephalin flocculation tests has been reported, indicating possible liver damage. Diborane may also damage the kidneys and nervous system [Genium 1987; Parmeggiani 1983; NJDH 1986]. In high concentrations, diborane may be irritating to the eye. Inhalation of this chemical has also been reported to cause double vision and difficulty in focusing, which disappeared shortly after exposure ceased [Grant 1986]. Contact with diborane in the liquid form may cause frostbite and cold burns of the skin or eye [DOT 1993, Guide 18].

* Signs and symptoms of exposure

1. Acute exposure: In acute poisoning, the symptoms are similar to those of metal fume fever: shortness of breath; coughing; tightness, heaviness, and burning in the chest; nausea; shivering; fever; and chest pain over the heart. Other symptoms of acute inhalation are drowsiness, dizziness, double vision, and difficulty in focusing. Signs appeared shortly after exposure or after a latent period of up to 24 hours [Sittig 1991]. Skin contact with the liquid will cause freeze burns. Eye burning and tearing may result from exposure to high concentrations of the gas [Genium 1987].

2. Chronic exposure: Chronic exposure causes lung irritation, headaches, dizziness, muscle fatigue, and weakness. There may also be occasional transient tremors [Parmeggiani 1983].

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 diborane and lead to worker exposures to this substance:

* The manufacture and transportation of diborane

* Use as a reducing agent in the synthesis of organic chemical intermediates; use in the conversion of olefins to trialkyl and triaryl boranes and primary alcohols, and as a polymerization catalyst for ethylene, vinyl, styrene, and butadiene; use as a chemical intermediate in production of other boron hydrides

* Use in electronics industry to improve crystal growth or to impart electrical properties in pure crystals; use as a doping agent for p-type semi-conductors

* Use as a rubber vulcanizer; use in the production of hard boron coatings on metals and ceramics

* Use as a component or additive for high-energy fuels, and as a flame-speed accelerator, and fuel for air-breathing engines and rockets

Methods that are effective in controlling worker exposures to diborane, 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 diborane 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 diborane, 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 respiratory and central nervous systems. 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 diborane 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 respiratory or central nervous systems.

* 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 diborane exposure. The interviews, examinations, and medical screening tests should focus on identifying the adverse effects of diborane on the respiratory or central nervous systems. 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 diborane.

WORKPLACE MONITORING AND MEASUREMENT

Determination of a worker's exposure to airborne diborane is made using a fluoropore filter in series with a charcoal tube (type 580-20, Barnebey-Cheney) impregnated charcoal (100/50 mg sections). Samples are collected at a maximum flow rate of 1.0 liter/minute until a minimum collection volume of 120 liter or maximum collection volume of 260 liters is reached. Analysis is conducted by inductively coupled plasma using atomic emission spectroscopy, ICP/DCP-AES. This method (OSHA modified NIOSH method # 6006) is described in the OSHA Computerized Information System [OSHA 1994] and is not yet validated. NIOSH Method No. 6006 can also be used to determine a worker's exposure to airborne diborane [NIOSH 1994b].

PERSONAL HYGIENE PROCEDURES

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

STORAGE

Diborane 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 diborane should be protected from physical damage and ignition sources, and should be stored separately from air, halogenated compounds, water, aluminum, lithium, other active metals, and any oxidized surfaces. Storage should be below 20 degrees C (68 degrees F) in a detached, well-ventilated, refrigerated area. Containers must be clean, dry, and free of oxygen, and should be checked periodically for decomposition. Dry nitrogen purges should be used for transfer operations.

SPILLS AND LEAKS

In the event of a spill or leak involving diborane, persons not wearing protective equipment and fully-encapsulating, vapor-protective 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. Ventilate potentially explosive atmospheres.

4. Stop the leak if it is possible to do so without risk.

5. Use non-sparking tools.

6. Use water spray to reduce vapors; prevent spray water from entering sewers.

7. If the source of the leak is a cylinder and cannot be stopped in place, remove the leaking cylinder to open air and repair the leak, or allow the cylinder to empty. If possible, dilute the leak with an inert gas and exhaust through a fume hood. Extreme caution should be taken since diborane will ignite spontaneously.

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

Employers owning or operating a facility at which there are 100 pounds or more of diborane must comply with EPA's emergency planning requirements [40 CFR Part 355.30].

* 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 diborane 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].

- Notify the emergency response commission of the State likely to be affected by the release [40 CFR 355.40].

- Notify the community emergency coordinator to the local emergency planning committee (or relevant local emergency response personnel) of any area likely to be affected by the release [40 CFR 355.40].

* 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 diborane 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 diborane 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 diborane 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 diborane. 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 diborane. The resistance of one PPE material to permeation by diborane is shown below:

(*) Not recommended, degradation may occur

To evaluate the use of this or other PPE materials with diborane, 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 diborane.

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.

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