Safety Bulletin U.S. Chemical Safety and Hazard Investigation Board No. 2003-03-B Reprinted SODIUM HYDROSULFIDE: PREVENTING H ARM November 2004 Introduction Sodium Hydrosulfide ince 1971, reported incidents involving liquid solutions of sodium Common synonyms: S hydrosulfide (NaHS) have resulted in 32 deaths and 176 injuries, most NaHS (NaSH) notably in the leather tanning and pulp and paper industries. The most Sodium bisulfide serious safety concern associated with NaHS is its capacity to produce Sodium sulfhydrate large amounts of deadly hydrogen sulfide gas (H2S) when it reacts with an Sodium hydrogen sulfide acid or is exposed to high heat. Sodium mercaptan Despite its pungent rotten egg odor, H2S can deaden the nerves that detect CAS No.: 16721-80-5 odors, thereby preventing those exposed from being able to smell life- UN No. (solution): 2922 threatening airborne concentrations. This condition is referred to as (Figure 2) “olfactory fatigue” and must be considered when designing NaHS safety systems. DOT Hazard Class: 8 (Figure 2) This Safety Bulletin is published to increase awareness of the hazards EPA Hazardous Waste No.: associated with NaHS and to outline safety practices to minimize the D003 potential for harm to workers and the public. with an acidic solution to Defining the Figure 1. Emergency produce H2S. responder in NaHS and H2S Problem Absent or inadequate protective gear. engineering controls, such as NaHS releases highly toxic H S if 2 ventilation or H2S detection mixed with an acid or if exposed to devices, coupled with excessive heat. Because it is inadequate PPE. corrosive, it is also potentially harmful to the skin and eyes.1 Inappropriate emergency response actions by workers and NaHS incidents typically involve emergency responders (Figure 1). the following three elements: This bulletin reviews selected An inadvertent spill, leak, or NaHS incidents that caused death mixing, whereby NaHS reacts and injury, for example: Delivery drivers inadvertently transferring NaHS into acid storage tanks. (See Whitehall 1 Although this bulletin addresses the hazards associated with NaHS solutions, Leather, Horween Leather, and its precautions also apply to other Prime Tanning case studies on sulfide-containing substances (e.g., sodium sulfide), which are often used pages 13–15.) interchangeably with NaHS, and which also generate H2S when mixed with acids. 2 CSB identified the following two Table 1 summarizes the general Figure 2. Shipping common management failures physical properties of NaHS placard with UN number during its review of catastrophic solutions. and DOT hazard class. NaHS-related incidents:2 Failure to identify and mitigate hazards during process system Table 1 design and engineering. Physical Properties of NaHS Failure to manage hazards that Molecular weight: 56.1 were not controlled through Specific gravity: good design and engineering. 1.152 (a)–1.376 (b) pH of solution: strongly alkaline (11–12) Physical Solution freezing point: -15ºC (a) – 40ºC (b) Characteristics Odor: rotten egg NaHS being allowed to mix with H S flammable limits acids in plant sewer systems. and Uses of NaHS 2 (% H S in air): (See Georgia-Pacific and 2 Lower: 4 Westvaco case studies on pages Typical NaHS solutions are pro- Upper: 44 13-14.) duced commercially by combining H2S with caustic soda (NaOH), as (a) 22% solution. Mixing of NaHS and an acid shown in the following reaction: (b) 60% solution. inside a common spill containment. (See Powell H2S + NaOH NaHS + H2O Duffryn case study on page 13.) NaHS is used in a variety of industries (Figure 3): The resulting finished solution has a pH of approximately 11.5. In the pulp and paper industry, Depending on its solution strength to remove lignin from wood (22 to 60 percent NaHS), it is chips. heated to 71 to 82 ºC to prevent In mining, as a flotation agent to CSB Safety Bulletins offer advisory crystallization. NaHS is sold information on good practices for separate impurities. managing chemical process hazards. commercially in both solution and Case studies provide supporting flake forms, with solutions In manufacturing, as a raw information. CSB Investigation accounting for about 80 percent of material or purifying agent. Reports comprehensively review all total U.S. production.3 the causes of an incident. In the leather-tanning industry, to remove hair from hides. U.S. Chemical Safety and Hazard 2 Investigation Board CSB compiled the incident data and Office of Investigations safety practices described throughout this Safety Bulletin during a compre- 2175 K Street NW, Suite 400 hensive review of NaHS incidents and Washington, DC 20037-1848 industry handling practices. 202-261-7600 3 Total U.S. production for all forms of http://www.csb.gov NaHS was approximately 269,000 tons in 2003. 3 Figure 3. NaHS use by industry sector. Leather tanning Miscellaneous Pulp & paper 10% 5% 42% Chemical & dye manufacturing 13% Copper flotation 30% The Innovation Group ACGIH: American Conference of Governmental MSDS: Material safety data sheet Industrial Hygienists Na: Sodium AIChE: American Institute of Chemical Engineers NaHS: Sodium hydrosulfide AIHA: American Industrial Hygiene Association NaOH: Sodium hydroxide ANSI: American National Standards Institute NAS: National Academy of Sciences ASSE: American Society of Safety Engineers NFPA: National Fire Protection Association ATSDR: Agency for Toxic Substances and Disease NIOSH: National Institute for Occupational Safety and Registry, DHHS Health, DHHS ºC: Degrees Celsius NLM: National Library of Medicine, National Institutes CAS: Chemical Abstracts Service of Health (NIH), DHHS CCPS: Center for Chemical Process Safety, AIChE NRC: National Response Center, USCG CDC: Centers for Disease Control and Prevention, NTSB: National Transportation Safety Board DHHS OSHA: Occupational Safety and Health Administration, CFR: Code of Federal Regulations U.S. Department of Labor CO2: Carbon dioxide PEL: Permissible exposure limit, OSHA CSB: U.S. Chemical Safety and Hazard Investigation pH: Potential of hydrogen Board PPE: Personal protective equipment DHHS: U.S. Department of Health and Human ppm: Parts per million Services PSM: Process safety management, OSHA DOE: U.S. Department of Energy PTFE: Polytetrafluorethylene DOT: U.S. Department of Transportation REL: Recommended exposure limit, NIOSH EPA: U.S. Environmental Protection Agency SCBA: Self-contained breathing apparatus ERPG: Emergency Response Planning Guidelines, AIHA SO2: Sulfur dioxide H: Hydrogen STEL: Short-term exposure limit H2O: Water TWA: Time-weighted average H2S: Hydrogen sulfide UN: United Nations HazCom: Hazard communication, OSHA USCG: U.S. Coast Guard IDLH: Immediately dangerous to life or health WEEL: Workplace emergency exposure limit, AIHA MIT: Massachusetts Institute of Technology 4 Eye Contact result in “gas eyes” or “sore eyes,” Health Hazard with symptoms of scratchiness, Summary Corrosivity hazard irritation, tearing, and burning. Because of the high pH of NaHS Symptoms are likely to disappear Because NaHS is corrosive, it solutions (approximately 11.5), when the exposure ends. Pro- presents a hazard to unprotected contact may severely irritate and longed exposure to concentrations 4 skin and eyes. However, its most burn the conjunctiva and cornea, of H2S above 50 ppm may cause serious hazard is its propensity to and may result in permanent tissue permanent damage or intense tearing, blurring of vision, and produce toxic H2S gas when mixed damage. with an acid or exposed to high heat pain when looking at bright light. sources such as a fire. The acid Hazard from generated H2S reaction chemistry is shown as: Exposure to low concentrations of Skin Contact + + H2S over several hours or days may Skin contact with NaHS may NaHS + Acid (H ) Na + H2S produce pain, irritation, redness 4 Inhalation The conjunctiva and cornea are the thin, (erythema), or burns. Because the transparent tissues that cover the outer symptoms of exposure severity may surfaces of the eye. The gases released by NaHS are corrosive and may contain high levels of H2S. Inhalation of H2S is Table 2 irritating to the nose and throat. Inhalation of H2S At higher concentrations, it can Concentration produce olfactory fatigue, a (ppm) Health Effects (a) buildup of fluid in the lungs (pulmonary edema), severe 0.05 Rotten egg odor detectable by most humans. shortness of breath, and death. 0.13–30 Obvious and unpleasant odor. Table 2 outlines the health effects of inhaling H S. 50–150 Olfactory fatigue (temporary loss of smell) and marked 2 dryness and irritation of nose and throat. Prolonged exposure may cause runny nose, cough, hoarseness, H S exposures may headache, nausea, shortness of breath, and severe lung 2 damage (pulmonary edema). cause olfactory fatigue 200–250 Worsening and more rapid onset of the above health Continuous exposure to low effects; possible death in 4 to 8 hours. concentrations (5 to 10 ppm) 300–500 Excitement, severe headache and dizziness, staggering, of H S or brief exposure to unconsciousness, and respiratory failure likely in 2 5 minutes to 1 hour; possible death in 30 minutes to higher concentrations (above 4 hours. 50 ppm) deadens the odor- detecting nerves in the nose and 500+ Rapid onset of severe toxicity, respiratory paralysis, and death. If not fatal, may cause long-term effects such as lessens the ability to smell memory loss, paralysis of facial muscles, or nerve tissue dangerous concentrations. The damage. higher the concentration of 800–1,000 May be immediately fatal after one or more breaths, H2S, the faster the onset of resulting in an instant unconsciousness or “knock-down” olfactory fatigue. effect. (a) Data from NIOSH, NLM, and ATSDR. 5 be delayed, affected skin should be treated immediately. (See the first Figure 4. NaHS incidents* by industry sector. aid guidance on page 12.) Ingestion Leather tanning Refining Unknown 1 Pulp & paper Ingesting a small amount of NaHS 5 1 14 in a single dose will likely produce Other only minor throat irritation or 6 burning of the esophagus. Ingesting a larger quantity, however—or small quantities over an extended period—may seriously damage the gastrointestinal tract.