Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 3 (2009)

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Summary Submariners live in an enclosed and isolated environment when at sea on a submerged submarine. Unlike workers who have respites from occupational exposures at the end of a shift or workweek, submariners are potentially exposed to air contaminants 24 h/day while their submarine is submerged. To protect submariners from potential adverse health effects associated with air contami- nants, the U.S. Navy has established 1-h and 24-h emergency exposure guidance levels (EEGLs) and 90-day continuous exposure guidance levels (CEGLs) for a number of the contaminants. EEGLs are defined as ceiling concentrations (concentrations not to be ex- ceeded) of chemical substances in submarine air that will not cause irreversible harm to crew health or prevent the performance of essential tasks, such as clos- ing a hatch or using a fire extinguisher, during rare emergency situations lasting 1-24 h. Exposures at the EEGLs may induce reversible effects, such as ocular or upper respiratory tract irritation, and are therefore acceptable only in emergen- cies, when some discomfort must be endured. After 24 h of exposure, the CEGLs would apply. CEGLs are ceiling concentrations designed to prevent immediate or delayed adverse health effects or degradation in crew performance that might result from continuous exposure to chemical substances lasting up to 90 days. In December 1995, the Navy began reviewing and updating the submarine exposure guidance levels. Because the National Research Council (NRC) Com- mittee on Toxicology (COT) had previously reviewed and provided recommen- dations for those and other types of exposure guidance levels, the Navy re- quested that COT review or when necessary develop EEGLs and CEGLs for a variety of substances. As a result of the Navy’s request, NRC convened a com- mittee in 2002 that reviewed and published two reports on 21 chemicals.1,2 As a 1 NRC (National Research Council). 2007. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 1. Washington, DC: National Academies Press. 3 

4 Exposure Guidance Levels for Selected Submarine Contaminants follow-on activity to that work, the Navy requested review of an additional five chemicals, and NRC convened a second Committee on Emergency and Con- tinuous Exposure Guidance Levels for Selected Submarine Contaminants in 2008. THE COMMITTEE AND ITS CHARGE Members of the committee were selected for their expertise in inhalation toxicology, neurotoxicology, regulatory toxicology, veterinary pathology, respi- ratory pathology, pharmacokinetics, pulmonary and occupational medicine, and human-health risk assessment. The committee was asked to review the U.S. Navy’s current and proposed 1-h and 24-h EEGLs and 90-day CEGLs for se- lected submarine contaminants and, where possible, to develop EEGLs and CEGLs for those selected chemicals that do not have existing or proposed lev- els. The committee was also asked to identify data gaps and to make recommen- dations for future research. Specifically, the Navy asked the committee to re- view guidance levels for acetaldehyde, hydrogen chloride, hydrogen fluoride, hydrogen sulfide, and propylene glycol dinitrate. APPROACH TO STUDY In conducting its evaluations, the committee reviewed relevant human and animal data and used data-selection criteria described in the NRC report Stand- ing Operating Procedures for Developing Acute Exposure Guideline Levels for Hazardous Chemicals.3 Where possible, primary references were used to derive the exposure guidance levels. Secondary references were used to support the estimates derived and the selection of critical end points. Whenever possible, studies that followed accepted standard scientific methods were selected as key studies (studies used to derive the exposure guidance levels). Inhalation- exposure studies were used to derive the EEGL and CEGL values; data on other routes of exposure were considered when that was appropriate. Human studies were preferred over animal studies. When epidemiologic and human experimen- tal studies were available, preference typically was given to human experimental studies because they were conducted in a controlled laboratory setting and al- lowed measurement of personal exposure and health effects relevant for deriva- tion of exposure guidance levels. The committee recognizes the need to consider 2 NRC (National Research Council). 2008. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 2. Washington, DC: National Academies Press. 3 National Research Council. 2001. Standing Operating Procedures for Developing Acute Exposure Guideline Levels for Hazardous Chemicals. Washington, DC: National Academy Press. 

Summary 5 the statistical power of a study involving a small number of subjects. However, the committee did not develop criteria for assessing the adequacy of a study’s statistical power, because individual studies, whether human or animal, were never used in isolation to derive an EEGL or CEGL value. When appropriate human data were not available, standard laboratory animal studies were used. A weight-of-evidence approach was used to select key studies and to ensure that the selected data were consistent with the overall scientific database. For derivation of the EEGL and CEGL values, the committee followed ba- sic guidance provided by the NRC report Criteria and Methods for Preparing Emergency Exposure Guidance Level (EEGL), Short-Term Public Emergency Guidance Level (SPEGL), and Continuous Exposure Guidance Level (CEGL) Documents4 but also considered the guidance for developing similar exposure levels provided in more recent NRC reports. Data on acute or short-term inhala- tion and ocular irritancy provided the basis of the EEGLs, whereas data on re- peated inhalation exposure data provided the basis of the CEGLs, and the effects of cumulative exposures were considered in deriving the CEGL. The most sensi- tive end points were emphasized for derivation of both exposure levels. The committee considered only health end points relevant to healthy young men on the assumption that no women are serving as permanent crew on submarines. When the key studies, health end points, and exposure levels were identi- fied, the application of uncertainty factors was considered in extrapolating from animals to humans and in extrapolating from lowest-observed-adverse-effect levels to no-observed-adverse-effect levels. When necessary, other factors were applied to account for critical data gaps or for potentially relevant variations in susceptibility. COMMITTEE RECOMMENDATIONS In this report, the committee recommends 1-h and 24-h EEGLs and 90-day CEGLs for acetaldehyde, hydrogen chloride, hydrogen fluoride, hydrogen sul- fide, and propylene glycol dinitrate. The recommendations are listed in Table S-1, and the Navy’s current values are included in the table for comparative pur- poses. The basis of the committee’s derivations and the specific recommenda- tions for research needed to improve the confidence of the derived exposure levels are provided in the individual chemical profiles. Most of the values derived by the committee are similar to or slightly higher than the current U.S. Navy values. However, the 24-h EEGL and 90-day CEGL derived by the committee for hydrogen sulfide were slightly lower than 4 National Research Council. 1986. Criteria and Methods for Preparing Emergency Exposure Guidance Level (EEGL), Short-Term Public Emergency Guidance Level (SPEGL), and Continuous Exposure Guidance Level (CEGL) Documents. Washington, DC: National Academy Press. 

6 Exposure Guidance Levels for Selected Submarine Contaminants TABLE S-1 Comparison of U.S. Navy’s Current Exposure Guidance Levels with Those Recommended by the Committee Current U.S. Navy Committee Recommended Chemical Exposure Level Value, ppm Value, ppm Acetaldehyde 1-h EEGL 10 25 24-h EEGL 6 12.5 90-day CEGL 2 2 Hydrogen chloride 1-h EEGL 5 9 24-h EEGL 2 3 90-day CEGL 1 1 Hydrogen fluoride 1-h EEGL 2 3 24-h EEGL 1 1 90-day CEGL 0.1 0.04 Hydrogen sulfide 1-h EEGL 10 10 24-h EEGL 3 2.8 90-day CEGL 1 0.8 Propylene glycol 1-h EEGL 0.15 0.2 dinitrate 24-h EEGL 0.02 0.02 90-day CEGL 0.01 0.004 the Navy values, and the 90-day CEGLs for hydrogen fluoride and propylene glycol dinitrate derived by the committee were about half the Navy’s values. The Navy may want to reconsider its 90-day CEGLs for hydrogen fluoride and propylene glycol dinitrate. RESEARCH RECOMMENDATIONS Since publication of the NRC reports Emergency and Continuous Expo- sure Guidance Levels for Selected Submarine Contaminants, Volumes 1 and 2, efforts have been made to characterize the submarine atmosphere better. How- ever, the committee emphasizes the importance of a continuing occupational- health program and the need to monitor the submarine atmosphere and to main- tain appropriate engineering controls to minimize the crew’s exposure to air contaminants. The committee did not address exposure to chemical mixtures. The poten- tial for antagonistic, additive, or synergistic interactions between contaminants in the submarine environment is subject to substantial uncertainty, remains largely unexamined, and needs to be studied. The committee recommends that 

Summary 7 the Navy examine event situations to determine toxicologically significant mix- tures to which the crew might be exposed in acute excursions. That is, what sys- tems could fail and what mixtures would be yielded as a result? As in the earlier reports, several of the chemicals evaluated in this report are sensory irritants. The derivation of quantitative environmental and occupa- tional exposure limits for sensory irritants is fraught with difficulty because measures of ocular and respiratory tract irritation experienced by human subjects are often subjective. The results of controlled human exposures to many sensory irritants typically use such descriptors as “mild” or “mild to moderate,” and the data on sensory-irritation thresholds can be highly variable. Research is needed to quantify the diverse methods and end points used in sensory-irritation studies so that the data can be used in public-health and occupational-health risk as- sessment with greater confidence. Finally, as noted earlier, the submarine is a unique environment in which workers are potentially exposed 24 h/day over periods of weeks or months. Few experimental studies examine continuous exposure, and more studies that repli- cate the submarine environment need to be funded and conducted.