The Occupational Safety and Health Act of 1970 emphasizes the need for standards to protect the health and safety of workers exposed to an ever-increasing number of potential hazards at their workplace. To provide relevant data from which valid criteria and effective standards can be deduced, the National Institute for Occupational Safety and Health has projected a formal system of research, with priorities determined on the basis of specified indices. It is intended to present successive reports as research and epidemiologic studies are completed and sampling and analytical methods are developed. Criteria and standards will be reviewed periodically to ensure continuing protection of the worker. I am pleased to acknowledge the contributions to this report on sulfur dioxide by members of my staff, the valuable and constructive comments presented by the Review Consultants on Sulfur Dioxide, the ad hoc committees of the American Academy of Occupational Medicine and the American Conference of Governmental Industrial Hygienists, by Robert B. O'Connor, M.D., NIOSH consultant in occupational medicine, and by William A. Burgess, NIOSH consultant on respiratory protection. The NIOSH recommendations for standards are not necessarily a consensus of all the consultants and professional societies that reviewed this criteria document on sulfur dioxide. Lists of the NIOSH Review Committee members and of the Review Consultants appear on the following pages.# I. RECOMMENDATIONS FOR
Sufficient technology exists to permit compliance with the recommended standard. The standard will be subject to review and will be revised as necessary.
"Exposure to sulfur dioxide" means exposure to a concentration of sulfur dioxide equal to or above one-half the recommended workroom environmental standard. Exposures at lower environmental concentrations will not require adherence to the following sections. Procedures for identification of exposure areas can be accomplished by time-weighted average (TWA) determinations by methods described in Appendices I and II or by any method shown to be equivalent in accuracy, precision, and sensitivity to the methods specified.
If "exposure" to other chemicals also occurs, for example from arsenic, then provisions of any applicable standard for the other chemicals shall also be followed.

# Section 1 -Environmental (Workplace Air) (a) Concentration
Occupational exposure to sulfur dioxide shall be controlled so that workers shall not be exposed to sulfur dioxide at a concentration greater than 2 parts per million parts of air (5 milligrams per cubic meter of air) determined as a time-weighted average exposure for an 8-hour work day.

# (b) Sampling, Calibration, and Analysis
Procedures for sampling, calibration of equipment, and analysis of environmental samples shall be as provided in Appendix I or by any method shown to be equivalent in accuracy, precision, and sensitivity to the method specified.
Section 2 -Medical (a) Comprehensive preplacement and annual medical examinations shall be provided for all workers subject to "exposure to sulfur dioxide."
The examination shall be directed toward but not limited to the eyes and the cardiopulmonary system; particular attention shall be focused on complaints of mucous membrane irritation and cough. An evaluation of the advisability of a worker's using negative-or positive-pressure respirators shall also be made. (a)

# Respiratory Protection
Engineering controls shall be used wherever feasible to maintain sulfur dioxide concentrations below the prescribed limit. Appropriate respirators shall be provided and used when a variance has been granted to allow respirators as a means of control of exposure to routine operations and while the application is pending. Administrative controls should also be used to reduce exposure. Respirators shall also be provided and used for nonroutine operations (occasional brief exposures above the TWA of 2 ppm and for emergencies); however, for these instances a variance is not required but the requirements set forth below continue to apply.
Appropriate respirators as described in Table 1-1 shall only be used pursuant to the following requirements:
(1) For the purpose of determining the type of respirator to be used, the employer shall measure the atmospheric concentration of sulfur dioxide in the workplace when the initial application for variance is made and thereafter whenever process, worksite, climate, or control changes occur which are likely to Increase the sulfur dioxide concentration. This requirement shall not apply when only atmospheresupplying positive pressure respirators are used. The employer shall ensure that no worker is being exposed to sulfur dioxide in excess of the standard either because of improper respirator selection, fit, use, or maintenance.
The respirator and cartridge or canister used shall be of the appropriate class, as determined on the basis of exposure to sulfur dioxide gas.
The employer shall provide respirators in accordance with Table 1-1 below and shall ensure that the employee uses the respirator provided.
(5) Respiratory protective devices described in (6) Respirators specified for use in higher concentrations of sulfur dioxide are permitted in atmospheres of lower concentrations.
Employees shall be given instruction on the use of respirators assigned to them, cleaning of the respirators, and how to test for leakage.
(8) Wherever bulk sulfur dioxide is handled, emergency and escape-type respirators shall be made readily available for each worker. (2) Type C supplied air respirator, demand type (negative pressure), with quarter or half mask facepiece.

# Less than or
(1) Gas mask with chin style canister equal to lOOx for acid gases.
(2) Gas mask with front or back mounted chest type canister for acid gases.
(3) Type C supplied air respirator, demand (negative pressure); pressure-demand; or continuous flow type with full facepiece.

# Greater than lOOx

# Emergency (No concentration limit)
(4) Self-contained breathing apparatus in demand mode (negative pressure) with full facepiece.
(1) Self-contained breathing apparatus in pressure-demand mode (positive pressure).
(2) Combination supplied air respirator, pressure-demand type, with auxiliary self-contained air supply.
(1) Self-contained breathing apparatus in pressure-demand mode (positive pressure)
(2) Combination supplied air respirator, pressure-demand type, with auxiliary self-contained air supply.

# Evacuation or escape
(1) Self-contained breathing apparatus (No concentration in demand or p_ '.ssure-demand mode limit) (negative or positive pressure).
(2) Gas mask with acid gas chest canister, and mouthpiece respirator. (2) Chemical safety goggles-cup-type or rubber-framed goggles, equipped with approved impact-resistant glass or plastic lenses, shall be worn whenever there is danger of eye contact, such as working with pipelines, valves, etc, which might leak and spurt liquid sulfur dioxide.
(3) Spectacle-type safety goggles-metal or plastic rim safety spectacles with unperforated side shields, or suitable all-plastic safety goggles may be used where continuous eye protection is desirable.
If use of this type of eye protection is mandatory, prescription lenses shall be provided for those employees who need them.
(4) Face shield-plastic shields with forehead protection may be worn in place of or in addition to goggles.

# (c) Work Clothing
(1) Work clothing should be changed at least twice a week or more frequently if required.
(2) Sulfur dioxide-wetted clothing, unless impervious, shall be removed promptly. (2)
Each container of sulfur dioxide shall be examined for leaks upon its arrival or upon filling and shall be reexamined periodically at least every 3 months.
(3) Prior to transferring sulfur dioxide from a storage container, an inspection shall be conducted to detect any gas leaks in the transport system (eg, cylinder seal with gas regulator, regulator apparatus, regulator seal with transport conduits, conduit system, etc).
(4) Cylinders of sulfur dioxide shall be secured so they cannot be damaged during transport or use.

# (b) Emergency Procedures
(1) Procedures for emergencies shall be established to meet foreseeable events. The irritant and choking properties of sulfur dioxide provide warning of overexposure and evacuation from the area should begin as soon as possible.
(2) Appropriate respirators shall be available for wear during evacuation.
(3) Where there is the possibility of sulfur dioxide contact on the eyes or skin, drench-type showers, eye-wash fountains, and cleansing facilities should be installed and maintained to provide prompt, immediate access by the workers.

# (c) Exhaust Systems and Enclosure
Exhaust ventilation and enclosure processes shall be used wherever practicable to control workplace concentrations. Systems shall be designed and maintained to prevent the accumulation or recirculation of sulfur dioxide into the workroom.
In addition, necessary measures shall be taken to ensure that discharge outdoors will not produce a health hazard to humans, animals, or plants.

# (d) General Housekeeping
Emphasis shall be placed upon cleanup, inspection and repair of equipment and leaks, and proper storage of materials.  In the case of intense exposures, even though they occurred frequently, there was believed to be no evidence of damage of a serious or a permanent type. It was surprising that the high frequency of symptoms of respiratory disease was the greatest' in the age groups under 50 where employment exposure time had been shortest. According to the author,  the most likely explanation was that because respiratory disease was rare in the younger age groups, the effect of small external insults was easier to detect than in the older age groups where respiratory disease from other causes was more common and small additions would be less noticeable.

# Anderson
In Later, the patient was exposed in a chamber to 10 ppm sulfur dioxide for 30 minutes.
On the following day, lesions again appeared but were weaker than had been previously experienced. The eruption disappeared the following night.
Another chamber exposure to 40 ppm sulfur dioxide for 10 minutes was given, after which the patient was permitted to breathe fresh air for an unspecified period and then returned to the chamber for another 10 minutes.
On the following day, an eruption again developed which was more severe than to the 10 ppm exposure. Regression of the lesions followed in approximately 2 days. It thus seems that these 2 reported cases were due to a systemic allergic reaction.
In       There is far less time lag than that experienced with laboratory analytical results. Rapid detecting units are valuable for determining whether a hazardous condition exists at a given location at a given time so that workers may be evacuated or suitable protective devices provided. In addition, industrial operators and process engineers need inexpensive and rapid tools for day-to-day evaluation of the atmospheric levels in a work area.
The accuracy of detector tubes is limited; at best they give only an indication of the contaminant concentration. In evaluating measurements performed with detector tubes, interferences, difficulty of endpoint readings, and possible calibration inaccuracies must all be considered.

# (d)

# Accuracy and Precision
At 2.5 ppm, the accuracy is 5% with a relative standard deviation of 4%. At 25 ppm, the accuracy and relative standard deviation can be improved to about 1%.

# (e) Advantages and Disadvantages
The samples are easily collected and conveniently shipped to the laboratory for analysis in glass vials.
The sulfuric acid formed is stable and nonvolatile, making this manner of collection of sulfur dioxide desirable.
The analysis is relatively rapid and simple.
Spillage from the impingers is possible and could be hazardous if spilled into molten metal.

# (f) Apparatus
(1) Absorber-glass midget impingers.
(2) Personal sampling pump with flowmeter capable of sampling at a rate of 1-2 liters/minute.
(3) 37 mm mixed cellulose ester filter, 0.8 micron nominal pore size.
(4) Necessary glassware.
(  If a specific item of information is inapplicable, the initials "n.a." (not applicable) should be inserted. (1) Toxic level for total compound or mixture, relevant symptoms of exposure, skin and eye irritation properties, principal routes of absorption, effects of chronic (long-term) exposure, and emergency and first-aid procedures.
(g) Section VI. Reactivity Data.
(1) Chemical stability, incompatibility, hazardous decomposition products, and hazardous polymerization.
(h) Section VII. Spill or Leak Procedures.
(1) Detailed procedures to be followed with emphasis on precautions to be taken in cleaning up and safe disposal of materials leaked or spilled. This includes proper labeling and disposal of containers holding residues, contaminated absorbents, etc.
(i) Section VIII. Special Protection Information.