By Paul Sohi
The Asphalt Institute’s (AI) Health, Safety and Environment (HSE) committee develops tools for members and the public that can be used to protect people working in the asphalt industry.
One tool developed during 2014 was guidance on how to prevent asphalt burns. The efforts highlighted the importance of immediate cooling of the asphalt to prevent further injury if someone got asphalt on their skin. The committee produced training materials devoted to assisting on-site first aid response for asphalt burns.
The burn treatment tools included a 13-minute video that included testimonials from asphalt workers that had suffered asphalt burns. The video also included simulated accident scenes highlighting the inherent dangers of working around hot asphalt and how to prevent burns. To accompany the video, the committee also developed and published a series of wallet cards and posters on recommended personal protective equipment (PPE).
Due to the success of the asphalt burn treatment tools, the committee accepted the task of developing a similar tool to increase hydrogen sulfide (H2S) awareness.
In 2016, the committee developed a wallet card to provide safety guidance on H2S. These small and rigid cards provide important warnings and serve as a reminder of hazards associated with working in an environment where H2S may be present.
The wallet card lists safety information to help asphalt workers safely enter areas where H2S may be present. The committee also developed a series of posters, tank clings and stickers that provide information that complements the wallet card to increase the awareness of the H2S dangers around asphalt.
Why should asphalt industry workers be concerned with H2S?
H2S is a naturally occurring gas contained in many of the world’s crude oils. It is formed by the anaerobic degradation of organic sulfur compounds in the crude oil when it is exposed to high temperatures or catalysts in the refining process. (Note that raw crude has significant H2S also. It does not have to be a refined product.)
H2S gas can cause multiple health effects if asphalt workers are overexposed and breathe it in. The health effects depend on how much hydrogen sulfide you breathe and for how long. H2S is particularly dangerous because it can impair the asphalt worker’s sense of smell at concentrations as low as 30 ppm and the asphalt worker can no longer detect the presence of H2S. Death can occur if a person is exposed to higher concentrations.
H2S toxicity concentrations and symptoms
2-5 ppm – Nausea, Headaches, Breathing Difficulties in Asthmatics
20 – Fatigue, Dizziness, Memory Problems
50-100 – Eye and Respiratory Irritation
200-300 – Severe Eye and Respiratory Irritation
500-700 – Staggering, Collapse
700-1,000 – Rapid Unconsciousness
1,000+ – Death
Workplace H2S exposure limits
ACGIH – 1 ppm TWA, 5 ppm STEL
OSHA – 20 ppm STEL
NIOSH – 10 ppm STEL
SCOE – 5 ppm (8-Hour TWA), 10 ppm STEL
(TWA is the 8-Hour Time Weighted Average, STEL is 15-minute Short Term Exposure Limit) ACGIH (Association Advancing Occupational and Environmental Health) OSHA (Occupational Safety and Health Administration) NIOSH (National Institute for Occupational Safety and Health) SCOEL (Scientific Committee on Occupational Exposure Limits)
Why is monitoring so important?
As can be seen from the above numbers, H2S is a potentially deadly gas often called “the silent killer” because the affected asphalt worker may never realize that they are in danger. That is why monitoring H2S is critical to ensure workers and the environment are protected from dangerous levels of H2S.
It is recommended that workers should always wear portable H2S monitors when working around potential H2S sources and be trained to seek safety should the monitor go off. An electrochemical sensor is the most practical type of H2S detector because its response time is in seconds when H2S is present. When selecting such a sensor, be sure it has the sensitivity and accuracy needed to support the current H2S guidelines.
H2S sensor considerations:
• Response time of 15 seconds or less
• Lower detection limit (sensitivity) of at least 0.5 ppm; 0.1 ppm resolution (smallest detectable change) and an accuracy of ± 5% over its calibrated range of at least 0-100 ppm are ideal.
• Accuracy of ± 0.05 ppm at 1 ppm (± 5%) to meet the requirement of a reliable alarm at 1 ppm
• Intrinsically safe design for use in areas where a combustible atmosphere may exist
• Low probability of false alarms
• High selectivity for H2S in the presence of interfering gases
Engineering solutions to reduce H2S in asphalt
One engineering solution used to reduce H2S in asphalt is called scavenging. A scavenger is a metallic chemical compound that reacts with H2S. It can be either used in a liquid or a solid form. Selecting the right scavenging system is important for the asphalt industry due to asphalt storage temperatures.
Also during the reaction process, it is best to select a scavenger that can convert H2S into a non-hazardous compound with no resulting emissions or hazardous byproducts.
Considerations for assessing scavenging technologies:
• The scavenger must be very reactive towards H2S in asphalt in order to minimize the required additive volume.
• The reaction product between the scavenger and H2S must be thermally stable, even under the high-temperature conditions of asphalt to ensure the chemical reaction is non-reversible.
• Asphalt has specific quality requirements, therefore the additive cannot change its physical attributes.
• Scavenger must be able to reduce H2S quickly and only react with H2S so that it is not consumed by other species within asphalt.
• Scavenger can only react with H2S that it comes in contact with – as the asphalt is mixed and agitated, more unreacted H2S can be liberated.
Several companies design custom scavenging technologies. They can provide technical assistance as needed. You should always consult a knowledgeable expert in this field for your individual situation.
Development of tools by the AI HSE committee is a scientific, iterative process. Asphalt industry experts with varying backgrounds consult third-party experts and published literature to collect and evaluate technical, scientifically-valid information.
The goal of the committee is to develop and publish the best, most practical tool possible. The asphalt burn treatment and the H2S tools are great examples of the fact that the HSE committee process works. The group is committed to the safety of asphalt workers.
Whenever possible, AI teams up with Eurobitume as both organizations share a common interest in safety. Future projects include producing a document on fire prevention and fire-fighting within asphalt storage facilities.
Sohi is the Director of Health, Safety and Environment for the Asphalt Institute.