In response to questions posed by researchers on a 2017 National Science Foundation study on the environmental impact of emissions from steam-cured cured-in-place pipe (CIPP) projects, the Trenchless Technology Center (TTC) at Louisiana Tech University has recently studied and published it results from a study on the same topic.
This comprehensive project, which was funded by NASSCO and peer-reviewed by a large group of industry stakeholders in North America, was undertaken to collect data from multiple projects under various climatic conditions and using varied sampling tools to determine the extent of potential impacts this method may have. Study objectives were to evaluate air emissions from steam cured CIPP installations and then determine potential impacts to workers and the surrounding community. The objectives were accomplished by measuring worker exposure to emissions onsite and immediately offsite. The construction sites selected represented a range of scenarios typical of CIPP installations from small to large diameter, various lengths, and mixed usage environments.
The locations were selected to capture jobsites in varies climates; however other limiting factors were considered (for example: availability, project and site characteristics). The site locations were in the warm, humid southern U.S. state of Louisiana; the dryer, higher elevated stated of Colorado and also the centrally located U.S. state of Missouri. This article aims to summarise the study, but the full results of the study are posted on the NASSCO website.
A full description of the methodologies and results can be found in the report. Key results worth highlighting are mentioned below. Based on the broad sampling and testing in this project, the only two locations where styrene levels could potentially pose any health risks were inside the transport/storage truck and near the emission stack (Image 1). Styrene emissions from inside the transport/storage trucks consistently measured between 100 ppm to 200 ppm, which could potentially pose health risks to workers if exposure durations exceeded 5 minutes. It is worth noting that none of the previously studies focused any of their testing at the transport truck location. It is also worth mentioning that the samples were being analysed for more than a dozen VOCs, but that styrene was the only VOC found at any measurable level. This finding was in contrast to other studies that suggested multiple VOCs were being detected at significant levels.
Results for emissions near the stacks were mostly lower than the transport trucks (Image 2), but potentially a risk if exposure durations approached 5 minutes. No measurement taken at a distance of 10 ft (3 m) or more from the termination manhole and/or exhaust stack exceeded exposure limits. In fact, those levels were far below guideline levels. Several variables like wind, temperature, and distance from the exhaust affect the dispersion of styrene, which most likely explains the range in concentration values.
Of note here is that although numerous measurements were taken at multiple sites using multiple methods, there was no corroboration of the extremely high values that had previously published by some researchers that reported measurements regularly exceeding 500 ppm. This calls into question the previously published higher levels which are what led to this study as there had been several other published studies in the past decade that had results more closely aligned with this TTC study.
Finally, measurements taken in homes near exhaust points yielded styrene concentrations less than 0.01 ppm. This suggests there is little potential danger of styrene emissions collecting in homes and rising to levels above exposure limits. Further research on this topic is being conducted by others researchers and industry currently. Data collected by sorbent tubes mounted on workers or at points to approximate worker exposure revealed no episode where the exposures averaged over the duration of the installation exceeded any threshold limits. This would suggest that CIPP installers experience safe long-term exposures to styrene.
The opening of the liner transport truck door represents a point in the CIPP installation process where there is potential exposure to dangerous levels of styrene. It is assumed, however, that styrene levels begin to dissipate the moment the liner transport truck is opened and could drop to acceptable short-term exposure levels soon after the door is opened. For these reasons, the TTC recommended:
- For those immediately entering the liner transport truck or storage unit, active air monitoring should be utilised at the initial opening of the truck or storage unit door to ensure a safe work environment.
- At the initial opening of the liner transport truck or storage unit door, suitable PPE should be worn by those immediately entering the truck or storage unit.
- This recommendation will ensure safe handling of the liner for nearly all potential levels of styrene.
The area very near the exhaust stack and/or termination manhole at a steam-cured CIPP installation site and any are contained within the visible plume of the exhaust points appear to be the locations on the jobsite where there is the greatest potential for exposure to airborne styrene above the limits set by OSHA, NIOSH and the EPA/CDC in the U.S. The styrene measurements taken at the exhaust points could represent styrene levels that endure for portions of the curing process that exceed 5, 15, or 30 minutes. For these reasons, the TTC team recommended:
- A conservative perimeter of 15 ft (4.5 m) be implemented around exhaust manholes/emission stacks during curing. This perimeter could be entered for less than 5 minutes. If this area is entered for longer than 5 minutes, suitable PPE should be used. This is similar to current practices in parts of Europe.
- Emissions stacks should be a minimum of 6 ft (1.8 m) tall to enhance the dispersion of emissions and lessen the likelihood of workers entering the perimeter from having to cross into the plume.
- This recommendation will ensure safe operations around the stack areas for the duration of the lining project.
In areas surrounding the exhaust stack, the data suggests that styrene dissipates rapidly and that exposure to styrene above regulatory guideline limits is unlikely outside of a 15 ft (4.5 m) radius around emissions points. Based on the data it is also unlikely that styrene levels would rise to a level that presented any danger to residents inside buildings. Future studies of CIPP emissions should focus on determining the time it takes liner truck emissions to dissipate and further evaluating specific task-oriented emission impacts. This is currently being studied by the researchers at the TTC.
The author acknowledges research team members from the TTC – PI: Dr Elizabeth Matthews; Co-PIs: Dr Shaurav Alam and Dr Sven Eklund; Researchers: Ashlesh Banjara, Hawa Hashm, Gazi Hossain, Dr Jason Howell and John Kraft; and from U.S. Army ERDC – Dr Anthony Bednar and Charles Laber. The authors acknowledge financial support from the National Association of Sewer Service Companies (NASSCO).