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 This information may be superseded by new developments in the field of industrial hygiene.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

INTRODUCTION

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 Recommendations may be superseded by new developments in these fields; readers are therefore advised to regard these recommendations as general guidelines and to determine whether new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

C(8)H(20)O(4)Si

* Structure

(For Structure, see paper copy)

* Synonyms

Ethyl silicate, condensed; silicon ethoxide; tetraethoxysilane;

tetraethyl orthosilicate; tetraethyl ester orthosilicic acid;

tetraethyl silicate; ethyl orthosilicate tetraethoxysilane

* Identifiers

1. CAS No.: 78-10-4

2. RTECS No.: VV9450000

3. DOT UN: 1292 29

4. DOT label: Flammable Liquid

* Appearance and odor

Ethyl silicate is a flammable, colorless liquid with a mild, sweet, alcohol-like odor. An air odor threshold of 17 parts per million (ppm) parts of air has been reported.

CHEMICAL AND PHYSICAL PROPERTIES

* Physical data

1. Molecular weight: 208.3

2. Boiling point (at 760 mm Hg): 168 degrees C (334 degrees F)

3. Specific gravity (water = 1): 0.94 at 20 degrees C (68 degrees F)

4. Vapor density: 7.2

5. Melting point: -77 degrees C (-106 degrees F)

6. Vapor pressure at 20 degrees C (68 degrees F): 1 mm Hg

7. Solubility: Practically insoluble in water; soluble in alcohol; slightly soluble in benzene.

8. Evaporation rate: Data not available.

* Reactivity

1. Conditions contributing to instability: Heat, sparks, or flames.

2. Incompatibilities: Contact between ethyl silicate and strong oxidizers, water, mineral acids, and alkalies should be avoided.

3. Hazardous decomposition products: Toxic gases and vapors (such as carbon dioxide, silicon dioxide, and carbon monoxide) may be released in a fire involving ethyl silicate.

4. Special precautions: None reported.

* Flammability

The National Fire Protection Association has assigned a flammability rating of 2 (moderate fire hazard) to ethyl silicate.

1. Flash point: 51.7 degrees C (125 degrees F) (open cup)

2. Autoignition temperature: Data not available.

3. Flammable limits in air (percent by volume): Lower, 1.3; upper, 23

4. Extinguishant: For small fires use dry chemical, carbon dioxide, water spray, or standard foam. Use water spray, fog, or standard foam to fight large fires involving ethyl silicate.

Fires involving ethyl silicate 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. 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 ethyl silicate 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. Do not get water inside the containers. 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 ethyl silicate.

EXPOSURE LIMITS

* OSHA PEL

The current Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) for ethyl silicate is 100 ppm (850 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 ethyl silicate of 10 ppm (85 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 ethyl silicate a threshold limit value (TLV) of 10 ppm (85 mg/m(3)) as a TWA for a normal 8-hour workday and a 40-hour workweek [ACGIH 1994, p. 21].

* Rationale for Limits

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

The ACGIH limit is based on the risk of irritation and on the effects noted in animals [ACGIH 1991, p. 640].

HEALTH HAZARD INFORMATION

* Routes of Exposure

Exposure to ethyl silicate can occur through inhalation, ingestion, and eye or skin contact [Sittig 1991, p. 793].

* Summary of toxicology

1. Effects on Animals: Ethyl silicate is an eye, mucous membrane, and respiratory irritant, a liver and kidney toxin, and a cerebral nervous system depressant. Acute inhalation exposure also causes profound anemia in animals [Hathaway et al. 1991]. The lowest lethal inhalation dose is 1,000 ppm for 4 hours and 700 ppm for 6 hours in rats and guinea pigs, respectively [NIOSH 1991]. The oral LD(50) in rats is 6,270 mg/kg; and the dermal LD(50) in rabbits is 5,878 mg/kg [NIOSH 1991]. Exposure of guinea pigs to 2,530 ppm of ethyl silicate for 4 hours produced irritation of the eyes and nose, lacrimation, respiratory difficulty, tremor, narcosis, and death. A postmortem examination of these animals revealed delayed but profound anemia, pulmonary edema, acute nephritis, and liver injury [NLM 1992]. Exposure to 400 ppm ethyl silicate for 7 hours a day for 30 days caused significant mortality in rats. The surviving animals developed kidney, liver, and lung damage [Hathaway et al. 1991]. In a group of rats, guinea pigs, and mice exposed to 88, 50, and 23 ppm respectively, for 7 hours a day, 5 days a week, for 90 days, only the mice exposed to 88 ppm demonstrated a decrease in kidney weight [ACGIH 1991]. Rats exposed three times to 500 ppm ethyl silicate for 7 hours developed pronounced kidney damage and slight lung irritation [NLM 1992]. Rats exposed 5 to 10 times to 125 ppm for 7 hours developed slight to moderate kidney damage that did not progress after 20 additional exposures [Hathaway et al. 1991]. Liquid ethyl silicate applied to the eye produces an immediate but transitory irritation that resolves within 24 hours, and exposure to ethyl silicate vapor in concentrations of 2,500 ppm for 2 hours caused opacification of the cornea in guinea pigs [Grant 1986].

2. Effects on Humans: Ethyl silicate is an eye, mucous membrane, and respiratory irritant in humans. By analogy with effects seen in animals, it may also cause liver and kidney damage, central nervous system depression, and anemia. At concentrations of 3,000 ppm, ethyl silicate causes extreme and intolerable irritation of the eyes and mucous membranes; at 1,200 ppm, it produces tearing of the eyes; at 700 ppm, it causes mild stinging of the eyes and nose; and at 250 ppm, it produces slight irritation of the eyes and nose [Hathaway et al. 1991].

* Signs and symptoms of exposure

1. Acute exposure: Signs and symptoms of acute exposure to ethyl silicate may include stinging of the eyes and nose, tearing of the eyes, respiratory difficulty, tremor, fatigue, narcosis, nausea and vomiting, signs of liver and kidney damage, and anemia. Eye contact with the liquid may produce tearing and irritation, and skin contact may produce drying, cracking, and inflammation [Sittig 1991].

2. Chronic exposure: Prolonged or repeated skin contact with liquid ethyl silicate may produce dermatitis [Genium 1989].

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 ethyl silicate and lead to worker exposures to this substance:

* The manufacture and transportation of ethyl silicate

* Use as a bonding agent for industrial buildings and investment castings, ceramic shells, crucibles, refractory bricks, and other molded objects

* Use as a protective coating for heat- and chemical-resistant paints, lacquers, and films

* Use in manufacture of protective and preservative coatings for protection from corrosion (primarily as a binder for zinc dust paints), chemicals, heat, scratches, and fire

* Use in the production of silicones; as a chemical intermediate in the preparation of soluble silica; as a gelling agent in organic liquids, as a coating agent inside electric lamp bulbs, and in the synthesis of fused quartz

* Use in textile industry in aqueous emulsions, deluster, and fireproofing; as a component of lubricants; as a mold-release agent; and as a heat-resistant adhesive

Methods that are effective in controlling worker exposures to ethyl silicate, 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 ethyl silicate 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 ethyl silicate, 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 system, liver, kidneys, and blood. 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 ethyl silicate 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 system, liver, kidneys, and blood.

* 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 ethyl silicate exposure. The interviews, examinations, and medical screening tests should focus on identifying the adverse effects of ethyl silicate on the respiratory system, liver, kidneys, or blood. 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 ethyl silicate.

WORKPLACE MONITORING AND MEASUREMENT

Determination of a worker's exposure to airborne ethyl silicate is made using an XAD-2 tube (100/50 mg sections, 20/50 mesh). Samples are collected at a maximum flow rate of 0.05 liter/minute until a maximum collection volume of 9 liters is reached. The sample is then treated with carbon disulfide. Analysis is conducted by gas chromatography using a flame ionization detector (GC/FID). This method is fully validated and is described in the OSHA Computerized Information System [OSHA 1994].

PERSONAL HYGIENE PROCEDURES

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

Clothing contaminated with ethyl silicate 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 ethyl silicate.

A worker who handles ethyl silicate 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 ethyl silicate or a solution containing ethyl silicate is handled, processed, or stored.

STORAGE

Ethyl silicate 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 ethyl silicate should be protected from physical damage and should be stored separately from strong oxidizers, water, mineral acids, and alkalies.

SPILLS AND LEAKS

In the event of a spill or leak involving ethyl silicate, 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. Do not touch the spilled material; stop the leak if it is possible to do so without risk.

5. Use non-sparking tools.

6. Water spray may be used to reduce vapors, but the spray may not prevent ignition in closed spaces.

7. Keep ethyl silicate out of a confined a space, such as a sewer, because of the possibility of an explosion, unless the sewer is designed to prevent the build-up of explosive concentrations.

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

9. For large liquid spills, build dikes far ahead of the spill to contain the ethyl silicate 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

Ethyl silicate 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 ethyl silicate; 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 ethyl silicate 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 ethyl silicate 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 ethyl silicate 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 ethyl silicate. 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 ethyl silicate. There are no published reports on the resistance of various materials to permeation by ethyl silicate.

To evaluate the use of PPE materials with ethyl silicate, 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 ethyl silicate.

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.

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AIHA [1985]. Hygienic guide series. Akron, OH: American Industrial Hygiene Association.

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NIOSH [1991]. Registry of toxic effects of chemical substances: Ethyl Silicate. 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.

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