(43w) Hydrogen Sulfide Exposure From Molten Sulfur- A Forgotten Hazard?

Molten sulfur is one of the most frequently transported hazardous materials (hazmat) in North America.  Typically, molten sulfur is transported by rail tank cars or over-the-road tank trailers.  According to the U.S. Department of Transportation Research and Special Programs Administration’s hazmat incident database, there have been 326 reported releases of molten sulfur in transportation between the years 1993 to 2003, inclusive.  Some incident reports indicate that high levels of hydrogen sulfide gas were released during the initial stages of unloading preparation.  In a few reported cases, the concentration of hydrogen sulfide was high enough to cause unloading personnel to lose consciousness, which then lead to further injury.  A review of the Occupational Safety and Health Administration (OSHA) accident report database confirms that over the last twenty years there have been four reported fatalities from hydrogen sulfide exposure associated with molten sulfur containers.

Over the last thirty years there has been a significant shift in the production of molten sulfur, moving from mining of geologic sulfur deposits (Frasch process) to environmental byproduct sulfur (Claus process).  This technology shift has increased the hydrogen sulfide hazard in molten sulfur.  A review of available Material Safety Data Sheets for molten sulfur suggests that the range of hydrogen sulfide concentrations and corresponding safe unloading and handling procedures for molten sulfur vary considerably among producers.  As a consequence, the unloading process may be performed in a manner ignorant of the possible high concentrations of hydrogen sulfide. 

In this paper we first summarize the key features of hydrogen sulfide-molten sulfur equilibrium that are relevant to this hazard.  Then we assess the relative risk of hydrogen sulfide exposure from a detailed analysis of molten sulfur shipping and accidental release statistics.  Then, we discuss a few case studies in which vented hydrogen sulfide gas from molten sulfur led to unexpected consequences for the unloading personnel.  We close our discussion with recommendations of how to prevent hydrogen sulfide exposure through a combination of unloading procedures, air monitoring and personal protection equipment.