PREFACE The Occupational Safety and Health Act of 1970 emphasizes the need for standards to protect the health and provide for the safety of workers exposed to an ever-increasing number of potential hazards at their workplace. The National Institute for Occupational Safety and Health has projected a formal system of research, with priorities determined on the basis of specified indices, to provide relevant data from which valid criteria for effective standards can be derived. Recommended standards for occupational exposure, which are the result of this work, are based on the health effects of exposure. The Secretary of Labor will weigh these recommendations along with other considerations such as feasibility and means of implementation in developing regulatory standards. It is intended to present successive reports as research and epidemiologic studies are completed and as 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 hydrogen sulfide by members of the NIOSH staff and the valuable constructive comments by the Review Consultants on Hydrogen Sulfide, by the ad hoc committees of the American Academy of Industrial Hygiene and the American Occupational Medical Association, and by Robert B. O'Connor, M.D., iii NIOSH consultant in occupational medicine. The NIOSH recommendations for standards are not necessarily a consensus of all the consultants and professional societies that reviewed this criteria document on hydrogen sulfide. A list of Review Consultants appears on page v i . o h n F. Finklea, M.D. Director, National Institute for Occupational Safety and Health iv The Division of Criteria Documentation and Standards Development, National Institute for Occupational Safety and Health, had primary responsibility for development of the criteria and recommended standard for hydrogen sulfide. The division review staff for this document consisted of# III. BIOLOGIC EFFECTS OF EXPOSURE
Monitoring for the evacuation limit shall be as provided in Appendix III, or by any method shown to be at least equivalent in accuracy, reliability, sensitivity, and speed to that specified.

# Section 2 -Medical
Medical surveillance shall be made available as outlined below to all workers subject to occupational exposure to hydrogen sulfide.
(a) Preplacement examinations shall include at least:
(1) Comprehensive medical and work histories with special emphasis directed to symptoms related to the eyes and the nervous and respiratory systems.
(2) Physical examination giving particular attention to the eyes and to the nervous and respiratory systems.
(3) A judgment of the worker's ability to use positive and negative pressure respirators.
(b) Periodic examinations shall be made available at least every 3 years to any workers who have been exposed to hydrogen sulfide above the recommended ceiling limit and shall include:
(1) Interim medical and work histories.
(2) Physical examination as described for the preplacement examination.
(c) During examinations, applicants or employees having medical conditions which would be directly or indirectly aggravated by exposure to hydrogen sulfide shall be counseled on the increased risk of impairment of their health from working with this substance and on the value of periodic physical examinations.
(d) Initial medical examinations shall be made available to all workers within 6 months after the promulgation of a standard based on these recommendations.
(e) In the event of adverse effect or illness known or suspected to be caused by exposure to hydrogen sulfide, a physical examination, as described above for preplacement, shall be made available.   For all work areas where there is a potential for the occurrence of emergencies involving hydrogen sulfide, employers shall take all necessary steps to ensure that employees are instructed in and follow the procedures specified below and any others appropriate for the specific operation or process.
( (2) Approved respiratory protection as specified in Section 4 shall be used by personnel essential to emergency operations.
( (1) Entry into confined spaces, such as tanks, pits, tank cars, barges, process vessels, and tunnels, shall be controlled by written permit or an equivalent system. Permits shall be signed by an authorized representative of the employer certifying that the confined space has been prepared as described in this section, and that precautions have been taken
to ensure that prescribed procedures will be followed. Signed permits shall be kept on file for 1 year after the date of use.
(     ( In general, at the present time, the more a method can be characterized as "wet chemical," the greater its analytical specificity and precision will be, the more suitable it will be for characterizing mixed gas streams at sources, the more limitations of temperature and portability will be encountered, and the higher will be the amount and technical sophistication of the maintenance required.
Alternatively, the more a system can be characterized as "coated-chip" or "semiconductor," the greater its cross-sensitivities will be (although detectors can be made with different cross-sensitivities for different applications), the more portable the system will be, the longer its reponse time may be, and the less frequent and sophisticated will be the required maintenance. Some semiconductor and related systems require a constant temperature, as do some wet-chemical systems.

# (c) Recommendations
For confirming compliance with the ceiling concentration limit, NIOSH should be taken to return to the previous effective set points because operators will sometimes turn off an alarm by raising the triggering level.
In selecting instruments, employers should weigh worker protection more heavily than analytical precision. If substances that give false positive readings by a detector system are themselves also toxic, they should be considered "additional sensitivities" rather than "interferences" of the system.

# Biologic Monitoring
No   In some cases, this may be advantageous: a detector that responds to hydrocarbons in addition to hydrogen sulfide may be useful for detecting leaks in petroleum production or refining facilities; some hydrogen sulfide monitors may be calibrated with carbon monoxide and conversion tables, and if the device is sensitive to another substance which is also toxic, eg,
mercaptans
Chemical substances should be listed according to their complete name derived from a recognized system of nomenclature. Where possible, avoid using common names and general class names such as "aromatic amine,"
"safety solvent," or "aliphatic hydrocarbon" when the specific name is known.
The "%" may be the approximate percentage by weight or volume (indicate basis) which each hazardous ingredient of the mixture bears to the whole mixture. This may be indicated as a range or maximum amount, ie, "10-40% vol" or "10% max wt" to avoid disclosure of trade secrets.