4 Tips for Choosing the Right H2S Analyzer

As part of the Biden administration’s environmental initiative, the U.S. Environmental Protection Agency (EPA) recently announced that natural gas processing (NGP) facilities would be required to report how they manage toxic gases and chemicals.

This ruling, expected to take effect on December 27, enables the inclusion of NGP facilities into the EPA’s Toxics Release Inventory program. Industrial facilities under this program constantly publish publicly-available info on its handling of harmful substances onsite. The EPA estimates that the ruling will affect 300 NGP facilities, most of which are situated near destitute communities. (1)

Also required under this new policy involves monitoring the emissions of at least 21 chemicals, one of which is hydrogen sulfide (H2S). This particular compound is all too common in the oil and gas industry, responsible for afflicting workers and civilians alike. Because of this, having a suitable H2S analyzer is encouraged, not just for the sake of compliance. (1)

This article will explain the well-known dangers of H2S in the oil and gas industry, as well as provide tips for NGP and other industrial facilities to mitigate its risks within and beyond the site.

The ‘rotten egg’ gas

Also known as ‘swamp gas’ or ‘sewer gas,’ H2S is a colorless gas characterized by a smell akin to rotten eggs. The compound is often a byproduct of the breakdown of organic matter, which is why it naturally occurs in fossil fuel deposits. In a way, the human body also produces H2S from breaking down food, though too little to have any detrimental effect.

According to the Agency for Toxic Substances and Disease Registry, the rotten egg smell is an indication that H2S concentrations may be at least 0.5 parts per billion (ppb). However, it also states that the stench is also a result of constant exposure to low and high concentrations. Using one’s nose to indicate H2S presence instead of thorough gas analysis is ill-advised. (2)

The Occupational Safety and Health Administration (OSHA) sets the H2S concentration ceiling at 20 parts per million (ppm), but fatigue and dizziness can happen even at such levels. Below is a list of possible symptoms and effects at higher concentrations. (2)

• At 50 ppm, slight gas eye and irritation of respiratory tract can occur after one hour.
• At 100 ppm, a person can lose their sense of smell within 15 minutes.
• At 200 ppm, prolonged exposure can lead to pulmonary edema.
• At 500 ppm, death can occur within one hour of exposure.
• At 1,000 ppm and above, death can occur in moments, if not immediately. (3)

Apart from the dangers of inhalation, H2S is also highly flammable. Ignition can happen under temperatures of over 500^o F; to put that into perspective, the tip of a lit cigarette can get almost twice as hot. Additionally, OSHA indicates that H2S has an explosive range between 4.5% and 42.5% in the air, beyond the permissible explosive limit. (3)

Saving Lives Through Analysis

The dangers of H2S exposure are clear enough for various agencies, such as the U.S. Chemical Safety Board, to iterate the importance of managing it. In 2019, it highlighted the deaths of two pumphouse workers in Texas. Its investigation uncovered a myriad of shortcomings––from poor onsite security to a lack of detection devices.

Industrial facilities should make a concerted effort to prioritize worker safety, such as investing in equipment like H2S analyzers. These devices use one of several H2S detection and analysis methods to provide real-time data to site managers. Having these to warn of unsafe H2S levels in advance can mean the difference in saving lives.

Tips for Choosing H2S Analyzers

With an assortment of H2S analyzers in the market, picking the right device for the facility will entail an extensive study of its needs. To help you out, here are some helpful tips:

1. Determine the lower limit of H2S detection

The first step involves determining how much H2S the facility has to deal with regularly. Each available method has a lower limit at which it can detect and analyze H2S effectively. If a site plans to take the initiative, it’ll need an analyzer capable of registering a hit in trace amounts.

Below are the lower detection limits of several analysis techniques, as outlined in this study:

• Lead acetate coated tiles – 0.03 ppm (usable between 0.003 and 0.3 ppm)
• Mercuric chloride paper tape – 0.5 ppb
• Sodium nitroprusside – 1 ppm or 20 ppb
• Methylene blue reaction – 1 ppb
• Infrared spectroscopy – above 10 ppm

Based on a 2011 revision to threshold limit values by the American Conference of Governmental Industrial Hygienists (ACGIH), experts recommend getting an analyzer with a lower detection limit of 0.5 ppm, with a resolution of 0.1 ppm. The device should also be able to return results in 15 seconds or less. (5)

Keep in mind that this value alone won’t determine the best H2S analyzer for a facility. Each method has its pros and cons and is better suited for specific environments.

2. Consider both fixed and portable systems

Analyzers come in either fixed or portable setups. While some experts believe fixed analyzers work better than portable ones, it boils down to the nature of the workplace. In some situations, both systems cover for each other’s disadvantages, allowing more in-depth protection.

Fixed analyzers enable 24/7 monitoring of a site or facility for any fluctuations in H2S levels. Some even allow the configuration of emergency shut-off measures when the readings reach a preset value. However, accurate readings require the proper positioning of sensors around the site or facility and demand constant power.

On the other hand, portable analyzers can instantly alert a user of H2S spikes, especially when working in the field. Some units feature GSM integration to enable remote monitoring from a central command. But portability comes at a cost: these devices can’t run 24/7 and require more frequent calibration to maintain accuracy.

One scenario that may warrant employing both systems is gas delivery. The storage facility will need a fixed analyzer to watch out for any H2S buildup. Truck drivers making the delivery runs will need a portable analyzer to do the same while en route to their destination.

3. Take interference into account

Any oil or gas facility can house different kinds of gases and chemicals, not just H2S. Any of these compounds in high concentrations can disrupt an H2S analyzer’s operation, resulting in inaccurate readings or false red flags.

Tests on a few electrochemical H2S analyzers have identified two such compounds (conditions set at 68^o F at 50% relative humidity, with atmospheric pressure at 1 atm):

• Phosphine (PH3) – Arguably more dangerous than H2S, phosphine can pose a danger to the human body at concentrations of 50 ppm. Interference to H2S analyzers can range between 55% and 60%.

• Mercaptans – Also referred to as thiols, mercaptans are abundant in facilities that extract or handle natural gas. Interference to H2S analyzers depends on the base chemical in the mercaptan; ethyl has a 34% interference rate, while methyl has 77%. (4)

Experts stress the importance of selectivity for gas-specific detectors. Recent research into novel detection technology has found that analyzers perform better at temperatures as low as 104^o F, achieving adequate gas sensitivity in under 14 seconds. It also shows that relative humidity, as mentioned earlier, becomes less of a factor under such conditions.

4. Enable consistent data logging

The ACGIH revisions also urge using H2S analyzers with built-in data logging features to help site managers respond to unusual trends. Their ability to record H2S levels from many moments ago will go a long way in mitigating accidents and injuries. (5)

Many units feature an internal memory bank large enough to store tens of thousands of data points. Wireless technology enables users to access and download these data points for analysis without traveling from one unit to the next. Such a network is also designed to work with legacy systems, further reducing operational costs.

Always Demand Accuracy

The tips explained in detail here will culminate in the single deciding factor in getting a suitable H2S analyzer: accuracy. The ACGIH revisions now require analyzers to have a margin of error of + 5% for a calibrated range of 0 to 100 ppm. This way, the device can reliably alert the site or facility when concentrations reach 1 ppm. (5)

But there’s another reason the industry should demand accuracy: conflicting readings. Oil and gas buyers and sellers use H2S analyzers to conduct their respective readings, so conflict arises when their devices register wildly different values. The party with the more accurate analyzer will be the winner of the dispute.

In such situations, both parties turn to standards published by the National Institute of Standards and Technology (NIST) for traceability testing. However, analyzer manufacturers have since been designing their units to comply with NIST calibration standards. As technology progresses, disputes like this may become rare in the future.

Conclusion

H2S analyzers serve several functions. Aside from helping keep accidents to a minimum, having one with high accuracy and reliability can put a facility in a position to settle reading disputes. They’re indispensable tools in the oil and gas industry, whether or not for legal compliance.

References

1. “Natural Gas Processing (NGP) Facilities Now Required to Report to EPA for the Toxics Release Inventory”, Source: https://www.jdsupra.com/legalnews/natural-gas-processing-ngp-facilities-5566785/
2. “Medical Management Guidelines for Hydrogen Sulfide”, Source: https://wwwn.cdc.gov/TSP/MMG/MMGDetails.aspx?mmgid=385&toxid=67
3. “Hydrogen Sulfide”, Source: https://www.osha.gov/hydrogen-sulfide/hazards
4. “ELECTROCHEMICAL SENSOR CROSS INTERFERENCE TABLE”, Source: https://www.indsci.com/en/training/general-gas-education/sensor-cross-interference-table/
5. “Monitoring H2S to Meet New Exposure Standards”, Source: https://ohsonline.com/articles/2011/09/01/monitoring-h2s-to-meet-new-exposure-standards.aspx