5.3 Permeation, Penetration, Degradation, and Compatibility
Key Takeaways
- Permeation is molecular movement of a chemical through intact protective material; breakthrough time is how long it takes until the chemical is detected on the inside — and it is chemical-, material-, temperature-, and concentration-specific.
- Penetration is bulk flow through openings the manufacturer did not intend to be a barrier: zippers, seams, visor gaskets, glove rings, pinholes, and incomplete closures.
- Degradation is physical damage to the material itself — swelling, shrinking, cracking, stiffness, discoloration, delamination — which can destroy barrier performance even before a lab would log breakthrough.
- Manufacturer compatibility charts rate specific chemical–material pairs; there is no universal best fabric, and a mixture is not the same as the neat chemical on the chart.
- Limited-use garments are typically discarded after contamination; reusable garments return to service only if the manufacturer allows decontamination and inspection shows permeation and degradation have not used the barrier up.
5.3 Permeation, Penetration, Degradation, and Compatibility
Quick Answer: Permeation is molecular movement of a chemical through intact clothing material; breakthrough time is the clock from first contact until the chemical is detected on the inside. Penetration is bulk liquid or vapor sneaking through zippers, seams, pinholes, visors, and glove interfaces. Degradation is physical damage to the polymer — swelling, cracking, stiffness, color change — that ruins the barrier. Compatibility charts are manufacturer- and chemical-specific. There is no universal best fabric. OSHA 1910.120 Appendix B states the same rule in regulatory English: protective-equipment materials protect well against some substances and poorly, or not at all, against others, and breakthrough time should exceed the work duration.
NFPA 470 technicians who can don Level A on a skill sheet still fail written items that ask how the suit actually fails. Plug, patch, and chlorine-kit work put product on the garment. If you cannot tell a zipper leak from molecular breakthrough, you will pick the wrong inspection, the wrong glove, and the wrong reuse decision.
Permeation — through intact material
Permeation is not a hole you can see. Molecules dissolve into the outer surface of the polymer, diffuse through the thickness, and evaporate or desorb on the inner surface. The clothing can look perfect while the chemical is already in the film. Laboratory permeation tests (the industry method technicians hear as ASTM F739) put liquid or gas on one side of a specimen and analyze the other side versus time.
Breakthrough time is the elapsed time from initial contact until the chemical is detected on the inside at the test’s detection rule. A common reporting benchmark on manufacturer charts is on the order of 480 minutes (an eight-hour industrial workday) for a “high” rating — that is a chart convention, not a promise that your 20-minute hot-zone job is automatically safe, and not a promise that a heated, flexed, mixed product will wait 480 minutes. Normalized breakthrough in permeation methods is often tied to a specified permeation rate (commonly 0.1 µg/cm²/min in ASTM F739 reporting). You do not need to recite the microgram figure on every item; you do need to know that breakthrough is a measured chemical-and-material event, not “the suit is yellow so it is good.”
Factors that shorten breakthrough time in the real world:
- Higher temperature (summer pavement, sun load inside an encapsulating suit, product still hot from a process)
- Higher concentration or neat liquid versus a dilute vapor
- Thinner material, abrasion, or stretch at knees, elbows, and glove crotches
- Prior permeation or incomplete decontamination (the polymer may already hold chemical)
OSHA’s selection sentence is operational: if you cannot find a material that provides continuous protection, breakthrough time of the protective material should exceed the work duration. That is why entry times, cylinder times, and clothing times have to be planned together — a 60-minute rated cylinder does not help if the glove breaks through in 12 minutes.
Penetration — through the openings
Penetration is bulk flow through a discontinuity: a zipper that is not fully seated, a storm flap left open, a pinhole from a ragged weld, a visor gasket, a glove-to-sleeve ring, a bootie seam, or a puncture from a drum chime. The polymer between the holes might have a heroic breakthrough time. The ensemble still failed because the chemical never had to permeate; it ran through the gap.
Liquid-penetration tests (the method often cited as ASTM F903) challenge material and sometimes seams with pressurized liquid. Field penetration is cruder: you see liquid on the inner glove, you smell product inside the hood, or a teammate’s visor fogs with something that is not sweat. Closures are the usual weak points. Encapsulating vapor-protective ensembles try to control this with gas-tight zippers, exhaust valves, and attached gloves. Splash garments accept more interface leakage because they were never sold as vapor envelopes.
Inspection before entry is a penetration hunt: zipper teeth, visor bond, exhaust-valve disks, glove rings, boot seams, and any scrape from the last incident. A pinhole is not “still Level A if the fabric chart is green.” It is a Level A-shaped rain coat.
Degradation — the material itself fails
Degradation is a physical or chemical change in the material: swelling, shrinking, becoming sticky or brittle, crazing, cracking, color change, bubbling, or delamination of a laminate. Degradation can appear before laboratory breakthrough, and it can accelerate permeation by opening the polymer network. Heat, ultraviolet light, repeated flexing, and incompatible solvents all degrade CPC.
Degradation is the failure mode you can often see or feel during use: the glove stiffens, the visor clouds, the sleeve wrinkles into a different size, or the fabric looks wet from the inside without a zipper leak. That is a doff-and-exit cue, not a toughness contest. Reusable garments that have degraded are out of service even if they were expensive.
The three-way comparison
| Failure mode | What moves | Path | What you notice | Typical exam tell |
|---|---|---|---|---|
| Permeation | Molecules | Through intact polymer | Often nothing visible; later odor, irritation, or a lab report | “Breakthrough time,” “molecular,” “chart minutes” |
| Penetration | Bulk liquid or gas | Zippers, seams, pinholes, visors, glove rings | Wetness at an interface, leak at a closure | “The zipper wasn’t sealed,” “pinhole,” “seam” |
| Degradation | The polymer changes | Material damaged (swell, crack, discolor, delaminate) | Visible or tactile change in the garment | “Suit became sticky/brittle/discolored” |
Memorize the triad as through, through-the-hole, and wrecked. Items that say “the fabric looked fine but the chemical was detected inside after 18 minutes” are permeation. Items that say “liquid appeared at the glove ring” are penetration. Items that say “the glove swelled and cracked” are degradation.
Compatibility charts — manufacturer, chemical, and condition
Manufacturers publish chemical-resistance / permeation charts for named products (a specific suit or glove model), not for “yellow plastic.” Ratings may use words (excellent / good / not recommended) or breakthrough-time bands. Charts assume specified temperature, usually continuous contact with the listed chemical (often the neat liquid), and a new specimen. They do not automatically cover:
- Mixtures (a 50/50 solvent blend can permeate faster than either component — synergy is real)
- Elevated temperature
- Flexing, pressure, and abrasion in a valve vault
- Previously used or poorly decontaminated garments
- A different product in the same color family
There is no universal best fabric. Butyl that shrugs off many polar compounds may fail against aliphatic hydrocarbons. A laminate with outstanding broad-chemical data may tear on a jagged flange. Viton™, nitrile, PVC, and Teflon™-type laminates each win some columns and lose others. The correct technician behavior is: identify the product (previous chapters), pull that manufacturer’s chart for that garment, confirm breakthrough exceeds the planned work interval, then inspect for penetration defects and degradation.
If the chart has no data, treat that as no recommendation, not as permission. Call the manufacturer’s 24-hour line, use a more conservative encapsulating system with known data, or change the tactic so skin contact is not required. Guessing from a neighboring chemical name on the same page is how people wear the wrong glove into a ketone.
Reuse versus limited-use
Limited-use CPC is generally one contamination cycle. Decontamination is for doffing safety, not to put the same disposable back on a shelf for next Saturday. Reusable CPC goes back only when:
- The manufacturer authorizes decontamination and reuse for that chemical exposure, and
- Inspection shows no degradation, no failed valves or visors, and no reason to believe permeation loaded the polymer.
Appearance after a wash is not a permeation test. Some chemicals continue to migrate after the outer surface is rinsed. When in doubt, out of service. The cost of a suit is not a JPR.
Scenario: the “green column” glove that still failed
A technician selects a reusable glove because the chart shows >480 minutes against the neat solvent on the SDS. The actual product is a warm mixture, the glove is flexed on a wrench for 15 minutes, and liquid appears inside the cuff. Possible stories, and they are not the same: the mixture did not match the neat-chemical column (compatibility); heat and flex shortened breakthrough (permeation under untested conditions); or the cuff-to-sleeve ring was the leak (penetration). If the glove is now swollen, degradation has also started. The exam wants you to name the mechanism, not to say “the suit was bad.” Charts start the selection. Work, temperature, mixtures, and closures finish it.
Put the three words on the inside of your helmet: permeate, penetrate, degrade. Then ask whether the chart chemical is the scene chemical.
A totally encapsulating suit shows no pinholes, the zipper is fully closed, and a laboratory report later finds the challenge chemical on the inner surface after 18 minutes of contact. Which process occurred?
Liquid product is found wet on the inner wrist at the glove-to-sleeve ring of a splash suit, while the glove polymer itself is not swollen. Which failure mode does that describe?
Which statement about chemical-protective-clothing compatibility is correct for technician selection?