Hydrogen sulfide (H2S) is a colorless, highly flammable and toxic gas notoriously known for its distinct, unpleasant odor similar to rotten eggs. There are a number of natural sources of H2S, including hot springs, volcanoes and decaying plant and animal matter. Humans also produce and use H2S in a number of different sectors, including oil and gas refining, mining, waste water treatment and textiles.

While H2S is most commonly known for its pungent smell, it emanates from various natural and industrial sources. To dive in deeper to hot springs and volcanoes, these vents emit H2S, a by-product of geothermal activity. Underground, decomposing organic matter, courtesy of bacteria, releases H2S into the atmosphere. In certain areas, where it is deprived of oxygen, it can create a breeding ground for bacteria that thrive on decay, producing H2S in the process. In the industrial realm, the petroleum and natural gas sectors contribute significantly to H2S emissions during extraction and processing. Other sources include wastewater treatment plants, pulp and paper mills, and chemical manufacturing facilities. Recognizing these diverse origins is crucial for implementing effective safety measures, as exposure to elevated H2S concentrations poses severe health risks and demands vigilant precautions to mitigate potential hazards.

Despite its hazardous nature, H2S gas has valuable applications in several industries. One key use is in the production of elemental sulfur. Invented by Carl Friedrich Claus, a German chemist working in England, the Claus process captures H2S gas from natural gas streams and refines it into sulfur, a crucial component in many industrial processes such as fertilizer production and rubber manufacturing. Farmers use H2S as an agricultural disinfectant and pesticide, and it can be found in some cutting oils – coolants and lubricants designed specifically for metalworking and machining processes – and other lubricants. Additionally, some nuclear power plants use hydrogen sulfide to produce heavy water, an alternative to regular water that enables nuclear reactors to use ordinary uranium fuel instead of enriched uranium. In the oil and gas industry, H2S removal is actually a critical step, not an application. It is utilized in refining processes to remove impurities from petroleum products, contributing to the purification of fuels. Products treated for H2S include crude oil, fuels and other refined petroleum products in storage tanks, tanker ships, rail-cars and pipelines. H2S can also be generated during refining processes, including hydrocracking and hydrolysis.

However, due to the dangers associated with H2S, its industrial use requires strict safety protocols and monitoring equipment to prevent incidents and environmental hazards. H2S can corrode pipes and equipment, and even exposure to low concentrations can pose serious health and safety risks to workers. 

According to the Occupational Safety and Health Administration (OSHA), H2S is one of the leading causes of workplace gas inhalation deaths in the US. Reports from the U.S. Bureau of Labor Statistics found that, over a seven-year period, there were 46 fatalities. The UK is no different, with a number of incidents each year and fines in excess of £60,000 being issued to a farm owner after two workers were engulfed by toxic H2S gas when they were tasked with opening the roof of a digester tank. With such statistics and violations, it is evident H2S presents many health hazards.

While the powerful smell can initially be extremely difficult to ignore, surprisingly the human nose can quickly become desensitized to the odor. Scientists from the Johns Hopkins University School of Medicine found that a protein called CNGA4 helps plug the ‘nose’ of odor receptor cells – neurons whose job is to detect smells and send that information to the brain as an electrical signal. As the neuron becomes desensitized, the signal closes and stops transmitting the information to the brain so that the smell can no longer be detected. While the ability to adapt to odors and desensitization is important to sustain overall well-being and prevent sensory overload, this makes H2S detection extremely challenging. Continuous exposure to H2S can have both short- and long-term effects, primarily affecting the respiratory and nervous systems. The health and safety risks often depend on how much a worker inhales and for how long. According to the Agency for Toxic Substances and Disease Registry, once someone has been seriously exposed, symptoms usually begin immediately. H2S interferes with cellular respiration, inhibiting the body’s ability to utilize oxygen properly. Being exposed to low concentration levels can cause irritation to the eyes, nose and throat while moderate levels can cause headaches, dizziness, nausea and vomiting, along with coughing and difficulty breathing. Serious exposure at higher levels can cause shock, convulsions and neurological disorders and lead to a coma or, in severe instances, death.

With such health and safety risks, it is crucial for workers who can be exposed to H2S to recognise and be aware of the hazards it presents. Given its toxic nature, strict adherence to safety protocols, proper ventilation and the use of personal protective equipment (PPE) are important in minimizing the risks associated with H2S gas exposure. Effective training and the use of advanced detection systems are essential to mitigate the hazards associated with H2S in industrial settings.

Keeping workers safe from harmful exposure to H2S requires a thorough understanding of safety regulations and standards set by the different regulatory bodies. In the US, OSHA acts as the primary regulatory body, mandating comprehensive guidelines that encompass permissible exposure limits (PELs), PPE requirements and effective hazard communication strategies. For instance, the OSHA PEL for H2S is 20 ppm and is not to be exceeded at any time during an 8-hour shift, except if the exposure concentration is 50 ppm then for no more than 10 minutes in an 8-hour shift, providing no other measurable exposure occurs. To help organizations navigate this hazardous risk in the workplace, OSHA has various industry-specific resources available and a fact sheet that provides useful information along with a concise summary of the OSHA requirements for the protection of employees. 

Simultaneously, the National Institute for Occupational Safety and Health (NIOSH), in the US, is also a valuable tool for H2S insights and information. While NIOSH doesn’t set mandatory safety regulations like OSHA that are legally enforceable, through research, it provides recommendations to support the development of best practices when handling H2S. Alongside recommended exposure limits (RELs), NIOSH emphasizes using a hierarchy of controls to minimize worker exposure. This means prioritizing eliminating the hazard altogether, followed by engineering controls (ventilation), administrative controls (work practices) and, finally, PPE. NIOSH also provides various documents on managing chemical safety and specific publications on preventing H2S in different industries.

In the UK, the Control of Substances Hazardous to Health Regulations 2002 (COSHH) is a legislative tool that states requirements imposed on organizations to protect their employees. This regulation specifically focuses on hazardous substances such as H2S and managing risk assessments, control measures and worker training. Similarly ISO 10418 is a standard that has been published to cover industry practice offshore for handling H2S.

Regardless of the location and the regulatory body enforcing the rules, adhering to these stringent standards is imperative for workplaces dealing with H2S, to prevent serious incidents and fatalities. Compliance with directives not only mitigates the potential hazards associated with H2S but also promotes a culture of safety through informed protocols and pre-emptive measures.

As OSHA mandates, PPE is required when workers are directly exposed to H2S or working at a site within close proximity to areas where the gas is present. When it isn’t possible to reduce H2S levels to meet or fall below OSHA’s permissible exposure limit through engineering and administrative controls, organizations must provide workers with respiratory protection and other PPE. Whenever respirators are used, the employer must have a respiratory protection programme that meets the requirements of OSHA’s Respiratory Protection standard (29 CFR 1910.134). This programme must include proper respirator selection, fit testing, medical evaluations and training. 

H2S is highly flammable and, if in concentrated contact with the skin, can result in chemical burns. This is why it’s important PPE is implemented to add an extra barrier of protection. This includes chemical-resistant and possibly flame-retardant  clothing, including coveralls and gloves, to shield the skin from potential exposure. Employing eye protection in the form of goggles or a face shield is crucial to prevent eye irritation or damage. To ensure comprehensive protection, steel-toed boots and a hard hat should be worn to safeguard against potential physical hazards.

As in most circumstances, PPE can act as a last line of defense against workplace hazards; this is no different when looking at the effects of H2S exposure. Its vital organizations adhere to PPE guidelines to prevent severe health and safety risks. Providing effective and relevant PPE is a fundamental part of the process to ensure a secure workplace for the organization and employees.

It is evident that prevention is the key to keeping workers safe from H2S exposure. However, it’s important to understand courses of action in the event of a H2S exposure or gas leak. When every second counts, a swift and well-coordinated emergency response and evacuation procedure are paramount. As in most incidents that require an emergency response, casualties usually occur in the first few seconds or more as people rushing to help coworkers involved in the incidents neglect to protect themselves. This is also the case for H2S exposure responses, where people can forget to equip themselves with their own breathing apparatus and PPE. 

In the event of a H2S leak or exposure, take immediate action to ensure the safety of individuals in the affected zone. Upon detection of H2S gas, activate alarms promptly, and communicate the danger using established protocols. Evacuate personnel to safe zones upwind of the release, as H2S is heavier than air and tends to settle in low-lying areas. Prioritize the use of respiratory protective equipment to minimize inhalation risks. Designated responders equipped with appropriate personal protective gear should be ready to isolate the source, if feasible, and implement containment measures. Clear communication channels and well-rehearsed evacuation routes are crucial elements of the emergency plan. Regular drills and training sessions ensure that all personnel are well-prepared to respond efficiently, minimizing the potential hazards associated with H2S exposure.

Internal evacuation procedures must be reviewed systematically, communicated clearly and understood across the entire organization to ensure correct steps can be swiftly taken to minimize the risks and control the situation.