Disclaimer: The information contained in these guidelines is intended for reference purposes only. It provides a summary of information about chemicals that workers may be exposed to in their workplaces. The information contained in these guidelines is current as of date of publication (September, 1996); recommendations may be superseded by new developments in the field of industrial hygiene. Readers are therefore advised to regard these recomendations as general guidelines and to determine whether new information is available.

OCCUPATIONAL SAFETY AND HEALTH GUIDELINE FOR TERT-BUTYL ACETATE

INTRODUCTION

This guideline summarizes pertinent information about tert-butyl acetate 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 Recommendations may be superseded by new developments; readers are therefore advised to regard these recommendations as general guidelines and to determine periodically whether new information is available.

SUBSTANCE IDENTIFICATION

* Formula

C(6)H(12)O(2)

* Structure

(For Structure, see paper copy)

* Synonyms

t-Butyl acetate; acetic acid, tert-butyl ester; acetic acid, 1,1-dimethyl ethyl ester; Texaco Lead Appreciator; TLA.

* Identifiers

1. CAS: 540-88-5.

2. RTECS AF7400000.

3. DOT UN: 1123 26.

4. DOT label: Flammable Liquid.

* Appearance and odor

tert-Butyl acetate is a flammable, colorless liquid with a fruity odor.

CHEMICAL AND PHYSICAL PROPERTIES

* Physical data

1. Molecular weight: 116.2.

2. Boiling point (760 torr): 97-98 degrees C (206.6-208.4 degrees F).

3. Specific gravity (water = 1): 0.89 at 20 degrees C (68 degrees F).

4. Vapor density (air = 1 at boiling point of tert-butyl acetate): 4.0.

5. Melting point: Data not available.

6. Vapor pressure at 20 degrees C (68 degrees F): Data not available.

7. Solubility: Insoluble in water; soluble in alcohol and ether.

8. Evaporation rate: Data not available.

* Reactivity

1. Conditions contributing to instability: Heat, sparks, and open flame.

2. Incompatibilities: Contact of tert-butyl acetate with nitrates, strong oxidizers, strong alkalies, and strong acids may cause fires or explosions.

3. Hazardous decomposition products: Toxic gases (such as carbon monoxide) may be released in a fire involving tert-butyl acetate.

4. Special precautions: None.

* Flammability

There is no National Fire Protection Association fire hazard rating for tert-butyl acetate; however, other sources rate this substance's fire hazard potential as severe.

1. Flash point: Between 16.6 and 22 degrees C (62 and 72 degrees F) (closed cup).

2. Autoignition temperature: Data not available.

3. Flammable limits in air (percent by volume): Lower, 1.5; upper, data not available.

4. Extinguishant: Use alcohol foam, carbon dioxide, dry chemical, water spray, or Halon to fight fires involving tert-butyl acetate.

Fires involving tert-butyl acetate should be fought upwind and from the maximum distance possible. Keep unnecessary people away; isolate hazard area and deny entry. Emergency personnel should stay out of low areas and ventilate closed spaces before entering. Containers of tert-butyl acetate 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 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. If a tank car or truck is involved in a fire, personnel should isolate an area of a half a mile in all directions. Firefighters should wear a full set of protective clothing, including a self-contained breathing apparatus, when fighting fires involving tert-butyl acetate. Firefighters' protective clothing may provide limited protection against fires involving tert-butyl acetate.

* Warning properties

The average air odor recognition threshold for n-butyl acetate, a chemical structurally similar to tert-butyl acetate, is 0.68 part per million (ppm) parts of air. Because this value is below the Occupational Safety and Health Administration (OSHA) current permissible exposure limit (PEL) of 200 ppm [29 CFR 1910.1000, Table Z-1-A], tert-butyl acetate is therefore likely to have adequate warning properties for the purpose of respirator selection.

* Eye irritation properties

No information is available on the specific concentration of tert-butyl acetate that causes eye irritation; however, this substance is known to be an eye irritant.

EXPOSURE LIMITS

The current OSHA PEL for tert-butyl acetate is 200 ppm (950 milligrams per cubic meter (mg/m³)) as an 8-hour time-weighted average (TWA) concentration [29 CFR 1910.1000, Table Z-1-A]. The National Institute for Occupational Safety and Health (NIOSH) has not issued a recommended exposure limit (REL) for tert-butyl acetate; however, NIOSH concurs with the PEL established for this substance by OSHA [NIOSH 1988]. The American Conference of Governmental Industrial Hygienists (ACGIH) has assigned tert-butyl acetate a threshold limit value (TLV) of 200 ppm (950 mg/m³) as a TWA for a normal 8-hour workday and a 40-hour workweek [ACGIH 1989, p. 14]. The OSHA and ACGIH limits are based on the risk of eye and respiratory tract irritation associated with exposure to tert-butyl acetate.

HEALTH HAZARD INFORMATION

* Routes of exposure

Exposure to tert-butyl acetate can occur via inhalation, ingestion, and eye or skin contact.

* Summary of toxicology

1. Effects on Animals: tert-Butyl acetate has not been tested for toxicity in animals. However, based on the effects of exposure to other acetate esters, tert-butyl acetate would be likely to cause eye, nose, and skin irritation and, at high concentrations, narcosis [Proctor, Hughes, and Fischman 1988, p. 105].

2. Effects on Humans: Exposure to tert-butyl acetate causes eye, skin, and respiratory irritation in workers. By analogy with the effects of exposure to similar esters, tert-butyl acetate may act as a central nervous system depressant at high concentrations [ACGIH 1986, p. 74].

* Signs and symptoms of exposure

1. Acute exposure: The signs and symptoms of acute exposure to tert-butyl acetate include itchy or inflamed eyes and irritation of the nose and upper respiratory tract. Exposure to tert-butyl acetate at high concentrations may cause headache, drowsiness, and other narcotic effects.

2. Chronic exposure: No chronic effects of exposure to tert-butyl acetate have been reported.

* Emergency procedures:

In the event of an emergency, remove the victim from further exposure, send for medical assistance, and initiate the following emergency procedures:

1. Eye exposure: If tert-butyl acetate or a solution containing this substance gets into the eyes, immediately flush the eyes with large amounts of water for a minimum of 15 minutes, lifting the lower and upper lids occasionally. Get medical attention as soon as possible.

2. Skin exposure: If tert-butyl acetate or a solution containing this substance contacts the skin, the contaminated skin should be flushed with large amounts of water for at least 15 minutes and should then be washed with soap and water. If irritation persists, get medical attention.

3. Inhalation: If tert-butyl acetate vapors are inhaled, move the victim at once to fresh air and get medical care as soon as possible. If the victim is not breathing, perform cardiopulmonary resuscitation; if breathing is difficult, give oxygen. Keep the victim warm and quiet until medical help arrives.

4. Ingestion: If tert-butyl acetate or a solution containing this substance is ingested, give the victim several glasses of salt water and then induce vomiting by having the victim touch the back of the throat with the finger or by giving syrup of ipecac as directed on the package. Do not force an unconscious or convulsing person to drink liquids or to vomit. Get medical help immediately. Keep the victim warm and quiet until medical help arrives.

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 and the location and proper use of emergency equipment.

EXPOSURE SOURCES AND CONTROL METHODS

The following operations may involve tert-butyl acetate and lead to worker exposures to this substance:

* Use as a solvent
* Use as an additive to improve the anti-knock properties of motor fuels

Methods that are effective in controlling worker exposures to tert-butyl acetate, depending on the feasibility of implementation, are

* Process enclosure,
* Local exhaust ventilation,
* General dilution ventilation, and
* Personal protective equipment.

The following publications are good sources of information on control methods:

1. ACGIH [1986]. Industrial ventilation--a manual of recommended practice. 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 MONITORING

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, placement of workers in jobs that do not jeopardize their safety or health, 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 monitoring program is intended to supplement, not replace, such measures. To place workers effectively and to detect and control work-related health effects, medical evaluations should be performed (1) before job placement, (2) periodically during the period 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 tert-butyl acetate, the examining physician 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 respiratory system. Medical monitoring for respiratory disease should be conducted using the principles and methods recommended by NIOSH and the American Thoracic Society.

A preplacement medical evaluation is recommended to assess an individual's suitability for employment at a specific job and to detect and assess medical conditions that may be aggravated or may result in increased risk when a worker is exposed to tert-butyl acetate at or below the prescribed exposure limit. The examining physician 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, or respiratory tract.

* Periodic medical examinations and biological monitoring

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 tert-butyl acetate exposure. The interviews, examinations, and medical screening tests should focus on identifying the adverse effects of tert-butyl acetate on the eyes, skin, or respiratory system. Current health status should be compared with the baseline health status of the individual worker or with expected values for a suitable reference population.

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 tert-butyl acetate.

* Medical examinations recommended at the time of job transfer or termination

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.

WORKPLACE MONITORING AND MEASUREMENT PROCEDURES

Determination of a worker's exposure to airborne tert-butyl acetate is made using coconut shell charcoal tubes (100/50 mg sections, 20/40 mesh). Samples are collected at a maximum flow rate of 0.2 liter per minute until a maximum air volume of 10 liters is collected. The sample is then desorbed with carbon disulfide. Analysis is conducted by gas chromatography using a flame ionization detector. The limit of detection for this procedure is 0.02 mg sample. This method is described in NIOSH Method 1450 [Esters I] [NIOSH 1984].

PERSONAL HYGIENE PROCEDURES

If tert-butyl acetate contacts the skin, workers should flush the affected areas immediately with plenty of water for 15 minutes, followed by washing with soap and water.

Clothing contaminated with tert-butyl acetate 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 tert-butyl acetate, particularly its potential to be irritating to the eyes and skin.

A worker who handles tert-butyl acetate should thoroughly wash hands, forearms, and face with soap and water before eating, using tobacco products, or using toilet facilities.

Workers should not eat, drink, or use tobacco products in areas where tert-butyl acetate is handled, processed, or stored.

STORAGE

tert-Butyl acetate 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 tert-butyl acetate should be protected from physical damage and should be stored separately from nitrates, strong oxidizers, strong acids, strong alkalies, heat, sparks, and open flame. Because containers that formerly contained tert-butyl acetate may still hold product residues, they should be handled appropriately.

LEAKS

In the event of a leak involving tert-butyl acetate, 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 leak:

1. Do not touch the spilled material; stop the leak if it is possible to do so without risk.

2. Notify safety personnel.

3. Remove all sources of heat and ignition.

4. Ventilate potentially explosive atmospheres.

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

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

7. For large liquid spills, build dikes far ahead of the spill to contain the tert-butyl acetate for later reclamation or disposal.

EMERGENCY PLANNING, COMMUNITY RIGHT-TO-KNOW, AND HAZARDOUS WASTE

MANAGEMENT REQUIREMENTS

The Environmental Protection Agency's (EPA's) regulatory requirements for emergency planning, community right-to-know, and hazardous waste management may vary over time. Users are therefore advised to determine periodically whether new information is available.

* Emergency planning requirements

tert-Butyl acetate is not subject to EPA emergency planning requirements under the Superfund Amendments and Reauthorization Act (SARA) (Title III).

* Reportable quantity requirements (releases of hazardous substances)

A hazardous substance release is defined by EPA as any spilling, pumping, pouring, emitting, emptying, discharging, injecting, escaping, leaching, dumping, or disposing into the environment (including the abandonment or discarding of containers) of hazardous substances. In the event of a release that is above the reportable quantity for that chemical, employers are required by the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) to notify the proper Federal authorities.

The reportable quantity for tert-butyl acetate is 5,000 pounds. If an amount equal to or greater than this quantity is released within a 24-hour period, CERCLA [40 CFR Part 302.6] requires employers to notify the National Response Center IMMEDIATELY at (800) 424-8802 (in Washington, D.C. at (202) 426-2675).

* Community right-to-know requirements

Employers are not required by Section 313 of the Superfund Amendments and Reauthorization Act (SARA) to submit a Toxic Chemical Release Inventory form (Form R) to EPA reporting the amount of tert-butyl acetate 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), EPA has specifically listed many chemical wastes as hazardous. Although tert-butyl acetate is not specifically listed as a hazardous waste under RCRA, EPA requires employers to treat any waste as hazardous if it exhibits any of the characteristics discussed above.

Providing more information about the removal and disposal of specific chemicals is beyond the scope of this guideline. EPA, U.S. Department of Transportation, 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 (202) 382-3000 (in Washington, D.C.) 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 tert-butyl acetate 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 emergency situations. If the use of respirators is necessary, the only respirators permitted are those 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 (see Table 1), an evaluation of the worker's ability to perform the work while wearing a respirator, the regular training of personnel, 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 NIOSH Respirator Decision Logic and the NIOSH Guide to Industrial Respiratory Protection.

Table 1 lists the respiratory protection that NIOSH recommends for workers exposed to tert-butyl acetate. The recommended protection may vary over time because of changes in the exposure limit for tert-butyl acetate or in respirator certification requirements. Users are therefore advised to determine periodically whether new information is available.

PERSONAL PROTECTIVE EQUIPMENT

Protective clothing should be worn to prevent skin contact with tert-butyl acetate. Chemical protective clothing should be selected on the basis of available performance data, manufacturers' recommendations, and evaluation of the clothing under actual conditions of use. No reports have been published on the resistance of various protective clothing materials to tert-butyl acetate permeation; however, the following materials have been tested against a chemically similar substance [n-butyl acetate] and may withstand permeation for more than 4 but fewer than 8 hours: polyvinyl alcohol, polyethylene/ ethylene vinyl alcohol, and Teflon. Since specific test data are not available for tert-butyl acetate, the information provided here should be considered as a guideline only. If permeability data are not readily available, protective clothing manufacturers should be requested to provide information on the best chemical protective clothing for workers to wear when they are exposed to tert-butyl acetate.

If tert-butyl acetate is dissolved in an organic solvent, the permeation properties of both the solvent and the mixture must be considered when selecting personal protective equipment and clothing.

Safety glasses, goggles, or faceshields should be worn during operations in which tert-butyl acetate might contact the eyes (e.g., through splashes of solution). Eyewash fountains and emergency showers should be available within the immediate work area whenever the potential exists for eye or skin contact with tert-butyl acetate. Contact lenses should not be worn if the potential exists for tert-butyl acetate exposure.

REFERENCES

ACGIH [1986]. Documentation of the threshold limit values and biological exposure indices. 5th edition. Cincinnati, OH: American Conference of Governmental Industrial Hygienists.

ACGIH [1989]. TLVs. Threshold limit values and biological exposure indices for 1989-1990. Cincinnati, OH: American Conference of Governmental Industrial Hygienists.

[CFR] Code of Federal regulations. Title 29 (Department of Labor), Parts 1910.1000 and 1910.1200. Washington, DC: U.S. Government Printing Office, Office of the Federal Register.

NIOSH [1984]. NIOSH manual of analytical methods. 3rd edition, Volume 1. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health.

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 [1987c]. 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 [1988]. Testimony of the National Institute for Occupational Safety and Health on the Occupational Safety and Health Administration's proposed rule: 29 CFR 1910, Docket No. H-020, August 2, 1988. NIOSH policy 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.

Proctor NH, Hughes JP, Fischman ML [1988]. Chemical hazards of the workplace. Philadelphia, PA: J.B. Lippincott Company.

BIBLIOGRAPHY

ACGIH [1986]. Documentation of the threshold limit values and biological exposure indices. 5th edition. Cincinnati, OH: American Conference of Governmental Industrial Hygienists.

AIHA [1988]. Odor thresholds for chemicals with established occupational health standards. Akron, OH: American Industrial Hygiene Association.

[CFR] Code of Federal regulations. Title 49 (Department of Transportation). Washington, DC: U.S. Government Printing Office, Office of the Federal Register.

[CFR] Code of Federal regulations. Title 29 (Department of Labor), Parts 1910.1000 and 1910.1200. Washington, DC: U.S. Government Printing Office, Office of the Federal Register.

DOT [1987]. 1987 Emergency response guidebook, guide 26. Washington, DC: U.S. Department of Transportation, Office of Hazardous Materials Transportation, Research and Special Programs Administration.

Forsberg K, Mansdorf SZ [1989]. Quick selection guide to chemical protective clothing. New York, NY: Van Nostrand Reinhold.

Hawley's condensed chemical dictionary [1987]. Sax NI, Lewis RJ. 11th edition. New York, NY: Van Nostrand Reinhold Company.

HSDB [1986]. tert-Butyl acetate. Bethesda, MD: The Hazardous Substances Data Bank, National Library of Medicine.

ITI [1986]. Toxic and hazardous industrial chemicals safety manual. Tokyo, Japan: International Technical Information Institute.

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

NIOSH [January 1981]. NIOSH/OSHA occupational health guidelines. 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. 81-123.

NIOSH [1987b]. 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. 85-114.

Proctor NH, Hughes JP [1978]. Chemical hazards of the workplace. Philadelphia, PA: J.B. Lippincott Company.

RTECS [1990]. tert-Butyl acetate. Bethesda, MD: Registry of Toxic Effects of Chemical Substances, National Library of Medicine.

Sittig M [1985]. Handbook of toxic and hazardous chemicals. 2nd edition. Park Ridge, NJ: Noyes Publications.

USCG [1984]. CHRIS (chemical hazards response information system) hazardous chemical data manual: tert-butyl acetate. Washington, DC: U.S. Department of Transportation, U.S. Coast Guard, Commandant Instruction M16465.12A.

Weast RC [1984]. CRC handbook of chemistry and physics. 64th edition. Boca Raton, FL: CRC Press, Inc.

Condition	Minimum respiratory protection**
Airborne concentration of tert-butyl acetate:
200 to 1000(+) ppm (5 × PEL)	Any air-purifying, half-mask respirator (including a disposable respirator) equipped with organic vapor cartridges, or Any air-purifying, full-facepiece respirator equipped with organic vapor cartridges, or Any powered, air-purifying respirator equipped with a loose-fitting hood or helmet and organic vapor cartridges, or Any powered, air-purifying respirator equipped with a tight-fitting facepiece and organic vapor cartridges
200 to 2000 ppm (10 × PEL)	Any supplied-air respirator equipped with a half mask and operated in a demand (negative-pressure) mode
200 to 4250(++) ppm (21.25 × PEL)	Any air-purifying, full-facepiece respirator equipped with an organic vapor canister, or Any powered, air-purifying respirator equipped with a loose-fitting hood or helmet and an organic vapor canister, or Any powered, air-purifying respirator equipped with a tight-fitting facepiece and an organic vapor canister, or Any supplied-air respirator equipped with a full facepiece and operated in a demand (negative-pressure) mode, or Any supplied-air respirator equipped with a hood or helmet and operated in a continuous-flow mode, or Any supplied-air respirator equipped with a tight-fitting facepiece and operated in a continuous-flow mode, or Any supplied-air respirator operated in a pressure-demand or other positive-pressure mode, or Any self-contained respirator equipped with a full facepiece and operated in a demand (negative-pressure) mode
Entry into unknown concentrations	Any self-contained respirator equipped with a full facepiece and operated in a pressure-demand or other positive-pressure mode, or Any supplied-air respirator equipped with a full facepiece and operated in a pressure-demand or other positive-pressure mode in combination with an auxiliary self-contained breathing apparatus operated in a pressure-demand or other positive-pressure mode
Firefighting	Any self-contained respirator equipped with a full facepiece and operated in a pressure-demand or other positive-pressure mode
Escape	Any air-purifying, full-facepiece respirator equipped with an organic vapor canister, or Any escape-type, self-contained breathing apparatus with a suitable service life (number of minutes required to escape the environment)

* The OSHA PEL is 200 ppm (950 mg/m³) as an 8-hour TWA. No NIOSH REL has been issued.
** Only NIOSH/MSHA-approved equipment should be used. Also note the following:

1. Respirators accepted for use at higher concentrations may be used at lower concentrations; respirators must not, however, be used at concentrations higher than those for which they are approved.

2. Air-purifying respirators may not be used in oxygen-deficient atmospheres.

(+) The maximum use concentration for organic vapor cartridges is 1000 ppm. tert-Butyl acetate is reported to cause eye irritation or damage; eye protection may be required.
(++) Represents 25 percent of the lower explosive limit