Failure Analysis Case Studies (Root Cause Determination)
Sometimes things go wrong. It is okay. The only true failures are those that are allowed to go uncorrected.
MAPL material characterization capabilities and decades of experience solving diverse material analysis challenges can help speed your Failure Mode and Effects Analysis (FMEA) and get you moving on to your next development milestone.
These case studies are presented in a way that emphasizes not just the end result, but the process that led to that result. Sharing our experience and growing in a mutually beneficial manner is part of what we're about at MAP Labs. The case studies below are presented in the order of increasing complexity. They highlight the types of critical thinking, experiment design, scientific analysis, and social engineering that often need to be employed to get to the true root of complex problems.
MAPL material characterization capabilities and decades of experience solving diverse material analysis challenges can help speed your Failure Mode and Effects Analysis (FMEA) and get you moving on to your next development milestone.
These case studies are presented in a way that emphasizes not just the end result, but the process that led to that result. Sharing our experience and growing in a mutually beneficial manner is part of what we're about at MAP Labs. The case studies below are presented in the order of increasing complexity. They highlight the types of critical thinking, experiment design, scientific analysis, and social engineering that often need to be employed to get to the true root of complex problems.
- Discoloration of Endoscope Sheath
- Electrical Leakage of Medical Endoscope
- Cracking of Respirator Membrane Valve
- Swelling of Endoscope Subsequent to Use in Medical Staff Training Device
- Tacky Surface of Thermoset Polyurethane - Coming Soon
- Unexplained Rapid Fluctuation in Polymer Physical Properties - Coming Soon
Cracking of Respirator Membrane Valve
Highly accelerated life testing (HALT) of an oxygen respirator system showed air leaks developing in some of the respirators. The Weibull distribution (histogram of how many cycles before failure) revealed a bimodal grouping with one group of respirators lasting much longer than the others.
Rubber membranes and a central piston were used to regulate the air flow in the respirator. These rubber membranes were expected to be at fault.
Close inspection of the membranes from the poorly performing group showed a few key differences.
Rubber membranes and a central piston were used to regulate the air flow in the respirator. These rubber membranes were expected to be at fault.
Close inspection of the membranes from the poorly performing group showed a few key differences.
- The central openings of the leaky valves were uneven and cracked
- The inner diameter of the leaky valves measured ~10% smaller than the reference good valves
- At higher magnification the surface of the leaky valves showed cracking
The specified construction of the membrane was Ethylene propylene diene monomer rubber (EPDM). The oxygen compatibility of EPDM is sufficient such that it should not develop surface cracking from such short duration exposures. The membranes were analyzed by FTIR for determination of polymer composition. The FTIR results indicated that the bad lots of membranes were composed of nitrile butadiene rubber (NBR), not EPDM. NBR is one of the worst gasket materials to use in an oxygen rich environments due to its susceptibility to oxidative degradation.
Further, the FTIR results also showed that the NBR membranes were softened with phthalate plasticizer. Phthalates easily migrate and diffuse to adjacent materials. Diffusion of the phthalate plasticizer into the grease/oil of the piston shaft was likely responsible for the shrinkage of the the membrane inner diameter. Hints of carboxylic acid structures (an oxidative degradation reaction product) are also evident in the damaged membrane FTIR spectrum.
Oxidative degradation of the NBR and the tighter fit on the piston shaft led to cracking of the membranes preventing an air-tight seal. The well performing membranes were all of EPDM composition, audits of vendor lot traceability prevented further early failures.
Oxidative degradation of the NBR and the tighter fit on the piston shaft led to cracking of the membranes preventing an air-tight seal. The well performing membranes were all of EPDM composition, audits of vendor lot traceability prevented further early failures.
Swelling of Endoscope Subsequent to Use in Medical Staff Training Device
Many endoscope technologies make use of staff training devices, meant to mimic the structure and properties of various parts of the human body. A technician noted swelling of an endoscope after use within a such a training device. The same type of device and endoscope had been in use for months with no issues previously observed.
The endoscope tubing materials and a piece of gel (which comprised most of the training device) were submitted for root cause determination of the polymer swelling. The materials were analyzed by Infrared Spectroscopy (FTIR). A new peak was observed in the swelled endoscope tubing at 1746cmˉ¹. This peak matched the ester peak of the vegetable oils that were detected in the training device gel by FTIR. Solvent extractions were performed to collect the oils from the as received endoscope tubing, the swelled tubing, and the training device gel material. Gas chromatography (GC) analysis of the gel oils indicated they were a mixture of vegetable and mineral (petroleum) oils. The vegetable oils were in the form high molecular weight triglycerides. The mineral oils from the submitted gel were high viscosity with an average molecular weight of roughly 480g/mol (C₃₄H₇₀). GC analysis of the oil extracted from the swelled tubing matched the vegetable oil triglyceride content of the gel, but the mineral oil content was much lower viscosity and molecular weight, averaging 297g/mol (C₂₁H₄₄). The discrepancy in the mineral oil molecular weight explained why there were suddenly problems with the new batch of training devices while no swelling had been observed in the past. The equilibrium percent swell increases drastically with lower molecular weight solvents. This relationship is described by the Flory-Reyner equation (bottom right). Additionally, the lower molecular weight oils diffuse faster so the swelling occurs with less exposure time. The Flory-Reyner equation can also be be used to probe the molecular weight and cross-link density of polymers by measuring percent swell in known molecular weight solvents. |
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Root Cause Determination - Discoloration of Endoscope Sheath
A field clinic reported black discoloration of disposable latex endoscope sheaths after they'd been used in diagnostic procedures. The goal was to determine where the black discoloration was coming from, how to prevent it, and assess any risk of damage to patients and equipment.
Background & Observations:
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Hypothesized Causes:
When formulating hypotheses for the cause of the discoloration the following categories of causes were considered:
When formulating hypotheses for the cause of the discoloration the following categories of causes were considered:
- Damage to the Polyurethanes. The discoloration only occurs near the urethanes, urethanes have poor glycerin resistance, though unlikely perhaps some die/pigments are being pulled from the urethanes.
- The Ultrasound Contact Gels are somehow responsible for the discoloration.
- There is something odd about this batch of latex that is leading to discoloration. ☆
- The disinfection processes are responsible for the color change. ☆
Experiment Results:
Though some of these potential causes of discoloration were more likely than others, an unbiased approach was taken. A test matrix was developed to evaluate all the various combinations of the materials potentially present. The test matrix resulted in two key observations:
The first of these observations did not come as a surprise. A literature review had already revealed that OPA can react with amines and amides to produce dark colored reaction products. It was expected that the latex contained some residual plant proteins which could be stained in this fashion. The literature review also revealed several cases of anaphylaxis and staining of patient body tissues after endoscopy procedures with probes that were contaminated with residual OPA.
The second observation was more surprising. It followed that if OPA reacting with plant proteins in the latex was the cause of the black stain, then some of the latex sheaths must have much more residual protein than others. FTIR examination of the latex sheaths confirmed that the sheaths that developed dark stains after OPA exposure had much higher protein levels. The literature search also revealed several studies on the difficulty of rinsing OPA from various medical device materials. The low water solubility of OPA and its high affinity for the polyurethane made the disinfectant especially difficult to rinse from the urethane components. |
The literature review had already shown many cases of complications from inadequate rinsing of endoscopes after disinfection with OPA. The easy corrective action is to make sure that the disinfection & rinse procedures are strictly adhered to. Extended soaking in OPA beyond the typically prescribed 10 minutes and insufficient rinse times could both led a buildup of OPA. Gas chromatography (GC) was performed as a demonstration of the ability to detect residual OPA on the surfaces of endoscopes. GC analysis would be an effective means to validate that the rinse procedures are sufficient to remove the residual disinfectant.
References
Cases of Black Staining of Patients after use of OPA Disinfected Endoscopes:
1. Horikiri, M., Park, S., Matsui, T., Suzuki, K., & Matsuoka, T. (2011). Ortho-phthalaldehyde-induced skin mucous membrane damage from inadequate washing. Case Reports, 2011(jan29 1), bcr0220102709-bcr0220102709. doi:10.1136/bcr.02.2010.2709
2. U.S. Food & Drug Administration. Adverse Event Report Number: 2084725-2010-00275 ADVANCED STERILIZATION PRODUCTS DISOPA SOLUTION BIOCIDES SOLUTIONS. (2010). Accessdata.fda.gov. Retrieved 2 June 2020, from https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfmaude/detail.cfm?mdrfoi__id=1835044
Studies on OPA Rinsability and Documented Healthcare Issues Related to Residual OPA on Endoscopes:
3. Miner, N., Harris, V., Lukomski, N., & Ebron, T. (2012). Rinsability of Orthophthalaldehyde from Endoscopes. Diagnostic And Therapeutic Endoscopy, 2012, 1-7. doi:10.1155/2012/853781
4. Senchak AJ, e. (2017). Oropharyngeal and laryngeal burn resulting from exposure to endoscope disinfectant: a case report. - PubMed - NCBI . Ncbi.nlm.nih.gov. Retrieved 2 June 2020, from https://www.ncbi.nlm.nih.gov/pubmed/18833537
5. Sokol, W. (2017). Nine episodes of anaphylaxis following cystoscopy caused by Cidex OPA (ortho-phthalaldehyde) high-level disinfectant in 4 patients after cytoscopy. - PubMed - NCBI . Ncbi.nlm.nih.gov. Retrieved 2 June 2020, from https://www.ncbi.nlm.nih.gov/pubmed/15316522
6. Venticinque SG, e. (2017). Chemical burn injury secondary to intraoperative transesophageal echocardiography. - PubMed - NCBI . Ncbi.nlm.nih.gov. Retrieved 2 June 2020, from https://www.ncbi.nlm.nih.gov/pubmed/1457
Reactions of OPA with Ammonia and Amines:
7. Do Minh, T., Johnson, A., Jones, J., & Senise, P. (1977). Reactions of phthalaldehyde with ammonia and amines. The Journal Of Organic Chemistry, 42(26), 4217-4221. doi:10.1021/jo00862a010
Cases of Black Staining of Patients after use of OPA Disinfected Endoscopes:
1. Horikiri, M., Park, S., Matsui, T., Suzuki, K., & Matsuoka, T. (2011). Ortho-phthalaldehyde-induced skin mucous membrane damage from inadequate washing. Case Reports, 2011(jan29 1), bcr0220102709-bcr0220102709. doi:10.1136/bcr.02.2010.2709
2. U.S. Food & Drug Administration. Adverse Event Report Number: 2084725-2010-00275 ADVANCED STERILIZATION PRODUCTS DISOPA SOLUTION BIOCIDES SOLUTIONS. (2010). Accessdata.fda.gov. Retrieved 2 June 2020, from https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfmaude/detail.cfm?mdrfoi__id=1835044
Studies on OPA Rinsability and Documented Healthcare Issues Related to Residual OPA on Endoscopes:
3. Miner, N., Harris, V., Lukomski, N., & Ebron, T. (2012). Rinsability of Orthophthalaldehyde from Endoscopes. Diagnostic And Therapeutic Endoscopy, 2012, 1-7. doi:10.1155/2012/853781
4. Senchak AJ, e. (2017). Oropharyngeal and laryngeal burn resulting from exposure to endoscope disinfectant: a case report. - PubMed - NCBI . Ncbi.nlm.nih.gov. Retrieved 2 June 2020, from https://www.ncbi.nlm.nih.gov/pubmed/18833537
5. Sokol, W. (2017). Nine episodes of anaphylaxis following cystoscopy caused by Cidex OPA (ortho-phthalaldehyde) high-level disinfectant in 4 patients after cytoscopy. - PubMed - NCBI . Ncbi.nlm.nih.gov. Retrieved 2 June 2020, from https://www.ncbi.nlm.nih.gov/pubmed/15316522
6. Venticinque SG, e. (2017). Chemical burn injury secondary to intraoperative transesophageal echocardiography. - PubMed - NCBI . Ncbi.nlm.nih.gov. Retrieved 2 June 2020, from https://www.ncbi.nlm.nih.gov/pubmed/1457
Reactions of OPA with Ammonia and Amines:
7. Do Minh, T., Johnson, A., Jones, J., & Senise, P. (1977). Reactions of phthalaldehyde with ammonia and amines. The Journal Of Organic Chemistry, 42(26), 4217-4221. doi:10.1021/jo00862a010
Electrical Leakage of Medical Endoscope
The video below covers an endoscope electrical leakage failure, the processes & tools we used to identify the root cause, and an overview of some component-level tests we can run to optimize device reliability.
The failure mode in this case was diffusion of 2-furoic acid and other electrolytes into the urethane, lowering the electrical resistance of the material.
Topics Covered in this video:
- Use of a Fluke Biomedical ULT800 Electrical Leakage Test Kit to find the source of an electrical leak.
- Use of a Thermo Fisher Scientific FTIR (Fourier Transform Infrared Spectrometer) to identify contaminants in the device.
- Component level Volume Resistivity testing by ASTM D257 using a Keysight Technologies B2987A electrometer.
- Importance of following manufacturer recommended usage and rinse times when performing high level disinfection of medical devices.
The failure mode in this case was diffusion of 2-furoic acid and other electrolytes into the urethane, lowering the electrical resistance of the material.
Topics Covered in this video:
- Use of a Fluke Biomedical ULT800 Electrical Leakage Test Kit to find the source of an electrical leak.
- Use of a Thermo Fisher Scientific FTIR (Fourier Transform Infrared Spectrometer) to identify contaminants in the device.
- Component level Volume Resistivity testing by ASTM D257 using a Keysight Technologies B2987A electrometer.
- Importance of following manufacturer recommended usage and rinse times when performing high level disinfection of medical devices.
Tacky Surface of Thermoset Polyurethane
Coming soon.