Fuels Technical Committee Advisory: Hydrogen Sulphide in Imported Fuels

Regulations for certain hazardous chemical agents (HCAs) have been in place since March 2021. PHILA MZAMO, head of communication at the Fuels Industry Association of South Africa (FIASA), explains the danger posed by hydrogen sulphide coming into the country.

Regulations gazetted by the Minister of Employment and Labour in March 2021 under the Occupational Health and Safety (OHS) Act regulate the levels of various HCAs in the workplace. The regulations stipulate the occupation exposure limit (OEL) or maximum airborne concentration of an HCA for either an eight-hour time-weighted average, a ceiling limit or a short-term exposure limit.

The OELs for hydrogen sulphide (H₂S) are 2ppm for an eight-hour time-weighted average and 10ppm ceiling limit, or maximum peak airborne concentration (determined over the shortest analytically practicable time, not exceeding 15 minutes).

In the past, H₂S has been found in both gasoline and diesel (gasoil) import cargoes (at >40ppm in the vapour phase for diesel, and more recently at >10ppm ceiling limit in gasoline). This presents a significant and real health, safety, security and environment (HSSE) risk to both vessel and tank farm operators and needs to be closely monitored.

H₂S is a colourless, toxic and flammable gas characterised by a pungent rotten egg smell and is irritating to the eyes, nose and throat. It can be detected by its odour, even at very low levels (<10ppb). It becomes generally unpleasant above 5ppm but begins to desensitise the nose at 30ppm. Continuous inhalation of the gas even at these low levels may cause paralysis of the sense of smell, making detection of the gas by its odour ineffective. Low-level exposure irritates the mucous membranes and may result in headache, dizziness or nausea.

At levels of 150ppm, H₂S paralyses a person’s sense of smell. Above 400ppm, there is a serious risk of pulmonary oedema (excess fluid in the lungs). Exposure for longer than 30 minutes at concentrations at >700ppm has been fatal, while exposure at 1,000ppm rapidly causes death.

Under the OHS Act regulations, the ceiling limit of 10ppm for H₂S is recommended not to be exceeded in the vapour phase of vessels’ tanks at discharge ports, prior to discharge. This must apply to all fuel cargo imports (excluding crude oil, for which different measures are taken). Each entity needs to implement the necessary interventions to ensure H₂S levels do not exceed 10ppm in imported cargoes arriving in SA ports.

In the breathable vapour phase, H₂S follows Henry’s Law*. Partitioning from the gasoil liquid phase, 1ppm of H₂S in liquid can be expected to produce >50ppm in vapour space, while 100ppm in liquid can equate to 20,000ppm in vapour space. Vapour phase levels can vary significantly according to the headspace volume, as well as fuel temperature and agitation.

Recommendations

1. Using Gas Tech / Draeger tubes, check and record H₂S levels in the vapour phase of vessels’ tanks at discharge ports, prior to discharge and in a safe manner (no confined space entry), as part of standard operating procedures according to ASTM D 5705.
2. Ensure calibrated test equipment is available to trained operators at all times.
3. Identify and implement an additional specification and test method such as IP 570 (determination of H₂S in fuel oils including marine residual fuels, distillates and petroleum blend stocks).
4. Maintain continuous awareness campaigns on the dangers of H₂S in the work environment to ensure employees are aware of associated hazards and how to adequately protect themselves.

* Henry’s law states that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid.