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Sodium Hydrosulfide: Preventing Harm

Overview

This CSB Safety Bulletin was issued to increase awareness of the hazards associated with sodium hydrosulfide (NaHS) and to outline safety practices to minimize the potential for harm to workers and the public. The bulletin states that NaHS can produce deadly hydrogen sulfide gas (H2S) when it reacts with an acid or is exposed to high heat. It summarizes multiple reported incidents from 1971 through 2004.

Incident Snapshot

Field Value
Facility / Company -
Location -
Incident Date 07/15/2004
Investigation Status The CSB issued this safety bulletin on July 15, 2004. This Safety Bulletin is published to increase awareness of the hazards associated with NaHS and to outline safety practices to minimize the potential for harm to workers and the public.
Accident Type Investigation Status: The CSB issued this safety bulletin on July 15, 2004. This Safety Bulletin is published to increase awareness of the hazards associated with NaHS and to outline safety practices to minimize the potential for harm to workers and the public.
Final Report Release Date 07/15/2004

What Happened

The bulletin summarizes several NaHS-related incidents.

  • On June 4, 1999, the driver of a tanker truck filled with NaHS inadvertently pumped the tanker contents into a storage tank partially filled with "pickle acid" (hydrochloric acid).
  • The shift supervisor, believing it to be pickle acid, directed the driver to unload it into a pickle acid storage tank.
  • The resulting reaction released H2S, which killed the driver and injured a plant employee.
  • On January 16, 2002, NaHS had recently been pumped from 15 tanker trucks into storage tanks at Georgia-Pacific.
  • Because of a leaking pump, NaHS accumulated in a spill containment pit that was connected to the plant acid sewer.
  • When the containment pit was drained, a relatively small quantity of NaHS reacted with acid in the sewer to produce H2S.
  • The H2S leaked through a faulty manway cover seal into the area where the contractors were working.
  • On April 10, 1995, the force from an explosion in a solvent storage tank fractured NaHS transfer piping.
  • Up to 300,000 gallons of NaHS spilled and mixed with a similarly large quantity of acidic cleaning solution.
  • The reaction released an enormous volume of H2S, which caused 337 people to seek medical evaluations and forced 2,000 downwind residents to evacuate.
  • On December 8, 1990, a large quantity of H2S formed during acid cleaning of a 20,000-gallon pulping solution pressure filter.
  • H2S was routinely produced inside the process vessel when the cleaning solution was used to dissolve NaHS-containing pulping filtrate.
  • On May 4, 1988, a 300,000-gallon storage tank containing pulping solution collapsed.
  • When the NaHS-containing pulping solution entered the sewer, it reacted with waste acids and produced H2S, which escaped via drains, vents, and manways.
  • On February 14, 1978, a substitute delivery driver unloaded a tanker truck of NaHS into a storage tank containing an acid.
  • A large volume of H2S was immediately generated, which led to evacuation of the entire plant and surrounding community.
  • On April 2, 1971, NaHS was inadvertently pumped into a tank containing acidic chrome tanning liquor, which has a pH of 3 to 4.
  • Approximately 160 gallons of NaHS had been transferred to the tank before one of the drivers noticed that workers inside the plant were collapsing.
  • NaHS had mixed with the chrome liquor to produce H2S.

Facility and Process Context

  • NaHS is used in the pulp and paper industry to remove lignin from wood chips.
  • NaHS is used in mining as a flotation agent to separate impurities.
  • NaHS is used in manufacturing as a raw material or purifying agent.
  • NaHS is used in the leather-tanning industry to remove hair from hides.
  • Most notably in the leather tanning and pulp and paper industries.
  • Georgia-Pacific, Naheola pulp and paper mill, Pennington, Alabama.
  • Powell Duffryn terminal fire, Savannah, Georgia.
  • Stone Savannah River pulp and paper mill, Wentworth, Georgia.
  • Westvaco paper mill, Covington, Virginia.
  • Horween Leather Company, Chicago, Illinois.
  • Prime Tanning Company, Berwick, Maine.
  • Whitehall Leather Company, Whitehall, Michigan.

Consequences

  • 32 fatalities reported in NaHS-related incidents from 1971 through 2004; specific case studies include 1 killed at Whitehall Leather, 2 killed at Georgia-Pacific, 1 killed at Stone Savannah River, 8 killed at Horween Leather, and 6 killed at Prime Tanning.
  • 176 injuries reported in NaHS-related incidents from 1971 through 2004; specific case studies include 1 injured at Whitehall Leather, 8 injured at Georgia-Pacific, 4 injured at Stone Savannah River, 43 injured at Horween Leather, and 10 injured at Westvaco.
  • Up to 300,000 gallons of NaHS spilled at Powell Duffryn and mixed with acidic cleaning solution; H2S continued to evolve from NaHS-saturated soil for more than 30 days at the Georgia-Pacific incident.
  • The force from an explosion in a solvent storage tank fractured NaHS transfer piping at Powell Duffryn; a 300,000-gallon storage tank containing pulping solution collapsed at Westvaco.
  • At least 10 plant or community evacuations; 337 people sought medical evaluations at Powell Duffryn; 2,000 downwind residents evacuated for more than 30 days at Georgia-Pacific; the entire plant and surrounding community were evacuated at Horween Leather.

Key Findings

Immediate Causes

  • NaHS reacts with an acid to produce H2S.
  • NaHS is exposed to excessive heat to produce H2S.
  • The resulting reaction released H2S.
  • NaHS mixed with acid in the sewer to produce H2S.
  • NaHS spilled and mixed with a similarly large quantity of acidic cleaning solution.
  • NaHS-containing pulping solution entered the sewer and reacted with waste acids and produced H2S.
  • NaHS was inadvertently pumped into a tank containing acid.
  • NaHS was inadvertently pumped into a tank containing acidic chrome tanning liquor.

Contributing Factors

  • Absent or inadequate engineering controls, such as ventilation or H2S detection devices, coupled with inadequate PPE.
  • Inappropriate emergency response actions by workers and emergency responders.
  • Failure to identify and mitigate hazards during process system design and engineering.
  • Failure to manage hazards that were not controlled through good design and engineering.
  • Inadequate evaluation of the potential for hazardous chemical mixing in the sewer system.
  • The shift supervisor had never received a shipment of NaHS and believed it to be pickle acid.
  • The substitute delivery driver was unfamiliar with plant operations and NaHS hazards, and was unsupervised by plant personnel.
  • There was no labeling on the tank to identify its contents or to warn of the potential hazard.
  • The driver created a makeshift coupling when he was unable to attach the line from the truck.
  • The containment pit drained to the acid sewer.
  • A leaking pump caused NaHS to accumulate in a spill containment pit.
  • Local exhaust ventilation normally controlled the H2S, but on the day of the incident H2S leaked from the system and accumulated inside the walled containment.
  • The plant sewer system routinely controlled storm runoff, spills, and discharged wastes, but when NaHS-containing pulping solution entered the sewer it reacted with waste acids and produced H2S.
  • The tank fill line coupling was designed to prevent inadvertent mixing.
  • NaHS had mixed with the chrome liquor to produce H2S.

Organizational and Systemic Factors

  • Georgia-Pacific management was unaware that the containment pit drained to the acid sewer.
  • Neither Georgia-Pacific nor the previous plant owners had adequately evaluated the potential for hazardous chemical mixing in the sewer system and the release of deadly amounts of H2S.
  • Plant personnel, contract workers, and emergency responders were unaware of and unprepared for the dangers.
  • The shift supervisor believed the NaHS shipment to be pickle acid.
  • The substitute delivery driver was unsupervised by plant personnel.
  • The delivery drivers had been instructed where to offload their tanker truck.
  • The incidents reviewed are not all-inclusive, but their number and severity clearly indicate that NaHS presents a serious hazard in the workplace.

Failed Safeguards or Barrier Breakdowns

  • Failure to identify and mitigate hazards during process system design and engineering.
  • Failure to manage hazards that were not controlled through good design and engineering.
  • Absent or inadequate engineering controls, such as ventilation or H2S detection devices.
  • Inadequate PPE.
  • Inappropriate emergency response actions by workers and emergency responders.
  • The containment pit drained to the acid sewer.
  • Faulty manway cover seal.
  • Local exhaust ventilation did not prevent the H2S release on the day of the incident.
  • No labeling on the tank to identify its contents or to warn of the potential hazard.
  • The tank fill line coupling was not used as intended and a makeshift coupling was created.
  • The plant sewer system did not prevent H2S from escaping via drains, vents, and manways.
  • There was no control to prevent NaHS-containing wastes from being flushed to acid-containing sewers.

Recommendations

  1. Recommendation ID: - | Recipient: - | Status: - | Summary: No specific recommendations were provided in the source JSON.

Key Engineering Lessons

  • Always treat sewers as extensions of the process.
  • Do NOT add wastes without analyzing for compatibility with other sewer contents.
  • Do NOT allow NaHS to come in contact with acids.
  • Do NOT flush to a sewer unless the sewer is designed and engineered to control the H2S that may be released.
  • NaHS can produce large amounts of deadly H2S when it reacts with an acid or is exposed to high heat.
  • Engineering controls such as ventilation and H2S detection devices are necessary but must be adequate for the hazard and maintained in service.
  • Process design must prevent inadvertent mixing of NaHS with acids, including in tanks, sewers, drains, vents, and manways.

Source Notes

  • Source priority 1 final report used as controlling authority for all NaHS incident facts.
  • The bulletin is a multi-incident safety bulletin rather than a single-incident investigation; the dataset preserves the bulletin's official terminology and case-study summaries.
  • No specific facility/company, location, or single incident date was provided for the bulletin as a whole beyond the bulletin release date.

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