When conducting respirable particulate sampling, environmental conditions and procedural factors can sometimes affect the accuracy and reliability of collected samples. One challenge that can arise in the field is PPI (personal particle impactor) overloading. Overloaded samples can bias results and make them unrepresentative of actual respirable dust exposures.
Understanding PPI Overloading
PPI samplers are disposable devices designed to collect respirable particulate matter, with built-in impactors that separate non-respirable particles. Under normal conditions, the sampler should provide accurate measurements of respirable dust. However, two scenarios can lead to overloading:
- Extreme particulate concentrations – In environments with very high concentrations of large particles, the PPI may collect more dust than it can handle. While sampler overloading cannot always be completely prevented, it’s important to note that OSHA’s Permissible Exposure Limit (PEL) for respirable dust is 5 mg/m³. A 2 L/min PPI sampler should be capable of handling typical concentrations over an 8–12 hour shift. If overloading occurs, it often indicates that actual dust concentrations far exceed the PEL. Large loose particles—often visible to the naked eye and ranging from 50 to 400 μm—can be found on the PPI filter and inside the collection stage.
- Particle break-off during handling or shipping – Non-respirable particles can detach from the collection substrate during sample transport, potentially skewing results if included in analysis.
A Client-Inspired Investigation
Our experience with PPI overloading became particularly relevant during the Los Angeles Wildfire cleanup. A client overseeing sample collection raised questions about severely overloaded samples, recognizing that the data did not represent the respirable fraction of dust. This scrutiny prompted us to investigate further.
We partnered with SKC, the PPI vendor, to examine impactor inlets from overloaded samples, both from this client and others. SKC reviewed the devices and identified scenarios that could lead to overloading. This collaboration resulted in practical recommendations to prevent overloading, both in the field and during shipment.
Solutions to Prevent PPI Overloading
SKC developed two cost-effective solutions to address common causes of sampler overloading:
- Particle shields – Reusable shields that help protect the sampler from large particles during sampling, priced around $5 each
- Cassette inlets – Disposable inlets that further reduce the risk of non-respirable particle contamination during shipping, priced around $1 each
SGS will have inventory early October. Please reach out to our team to inquire.
Read more from SKC here.
Key Takeaways
- Listening to client concerns is critical – The detailed questions from one client led to an industry-wide improvement.
- Vendor collaboration matters – SKC’s willingness to investigate, review devices, and develop practical solutions highlights the importance of strong vendor partnerships.
- Industry-wide benefits – The combination of client vigilance, our expertise, and vendor support can help improve sampling accuracy for respirable dust across a variety of workplaces.
Preventing PPI overloading ensures that collected samples truly represent the respirable* fraction of dust, providing reliable data for industrial hygiene decision-making. By following these recommendations, IH professionals can reduce the risk of biased results and better protect worker health.
* Please note: A thoracic particulate PPI model is available; however, this blog focuses specifically on respirable particulate.