13.1 Routes of Exposure
Key Takeaways
- OSHA 29 CFR 1910.120(q)(6)(iii)(I) requires technicians to understand basic chemical and toxicological terminology and behavior, including how a product actually enters the body.
- Inhalation of vapors, gases, aerosols, and dusts is the most common occupational route; it is also the fastest way a failed self-contained breathing apparatus (SCBA) becomes a medical emergency.
- Skin absorption is a real technician hazard for lipid-soluble products — pesticides, phenol, hydrofluoric acid (HF), and nerve agents — even through intact skin and through a pinhole in a glove.
- Ingestion is usually a hygiene and rehabilitation-area failure (contaminated hands, eating or drinking in dirty CPC, off-gassing suits); injection is sharps, high-pressure product, or contaminated trauma; the eyes are a separate mucous-membrane route.
- Match the route to the control: inhalation → respirator; skin → chemical protective clothing (CPC); ingestion → decontamination and hygiene; injection → puncture-resistant protection and medical care; ocular → facepiece or chemical goggles.
13.1 Routes of Exposure
Quick Answer: A hazardous materials technician stops a release and keeps the product out of people. Occupational Safety and Health Administration (OSHA) 29 CFR 1910.120(q)(6)(iii)(I) requires you to understand basic chemical and toxicological terminology and behavior. Start with the route of exposure: inhalation, skin absorption, ingestion, injection, and ocular. Inhalation of vapors, gases, aerosols, and dusts is the most common occupational route. Match the route to the control: respirator for air, chemical protective clothing (CPC) for skin, decontamination and hygiene for the mouth, puncture-resistant protection for injection, and a facepiece or chemical goggles for the eyes.
National Fire Protection Association (NFPA) 470 (2022) does not give toxicology its own Job Performance Requirement (JPR) number, but every Analyze and Plan decision in Chapter 11 assumes you know how the product gets in. Chapter 7.1 already split contamination (material where it should not be) from exposure (a dose through a route of entry). This section is the route map. If you cannot name the pathway, you cannot pick self-contained breathing apparatus (SCBA), CPC, or a decontamination method on purpose.
Many first-aid cards list four routes and fold the eyes into “absorption.” Technician items still test ocular contact as its own problem — mucous membranes, splash, and vapor irritation — so this guide treats five pathways. The four-route card is not wrong; it is incomplete for a visor leak.
Five routes, five controls
| Route | What actually enters | Typical field sources | Primary technician control |
|---|---|---|---|
| Inhalation | Vapors, gases, aerosols, mists, fumes, smoke, dusts | Open valves, vapor clouds, displaced confined-space atmospheres, powder dumps | Atmosphere-supplying respirator (usually positive-pressure SCBA) until monitoring says otherwise |
| Skin absorption | Liquid, mist, or vapor through intact or damaged skin; especially lipid-soluble molecules | Glove pinholes, soaked inner clothing, prolonged wet contact, permeation of CPC | CPC selected for the chemical; glove rings; minimize contact time; skin notation on exposure limits |
| Ingestion | Swallowed product or residue transferred hand-to-mouth | Eating or drinking in rehab with dirty hands, chewing gum, contaminated inner gloves, bottles handled with outer gloves | Technical decontamination before rehab, no food or drink with contaminated hands, keep dirty CPC out of the rest area |
| Injection | Product forced under the skin or into a wound | Sharps at clandestine labs, high-pressure hydraulic or paint injection, jagged metal, broken glass, contaminated trauma | Puncture-resistant gloves where the task warrants them; do not treat a high-pressure pinhole as “just a cut” |
| Ocular | Splash or vapor on the eyes and mucous membranes | Drum bung spray, wind-driven mist, a leaking visor, rubbing eyes with a contaminated glove | Full facepiece (SCBA or respirator) or chemical splash goggles plus face shield as the ensemble requires |
The table is a planning tool, not a promise that one control covers every route. Level A exists because some products attack skin and lungs at the same time. Failed SCBA does not make the CPC irrelevant, and a pinhole glove does not make the air clean.
Inhalation — the occupational default
The lungs are a huge, wet, thin membrane sitting on a blood supply. That is why inhalation is the most common occupational route and why OSHA 1910.120(q)(3)(iv) puts positive-pressure SCBA on emergency responders who face an inhalation hazard until the incident commander can show, with air monitoring, that a lower level of respiratory protection will not create hazardous exposures.
What you inhale is not always a “gas” in the textbook sense:
- Gases (chlorine, ammonia, carbon monoxide, hydrogen cyanide) occupy the space you walk into.
- Vapors ride off liquids (solvents, gasoline, anhydrous-ammonia boil-off).
- Aerosols, mists, and fumes carry droplets or solids that still land in the airway.
- Dusts (pesticides, metal powders, some oxidizers) are solids you can still breathe.
Heavier-than-air vapors pool in basements, ditches, and sewers; lighter-than-air products collect at ceilings and eaves. Chapter 11 already taught you to put the probe where the product lives. Toxicology adds the reason: the probe location is the inhalation zone you are about to occupy.
A failed SCBA — lost facepiece seal, empty cylinder, bypassed regulator, or a technician who cracked the mask to “talk” — turns the fastest occupational route loose at the highest concentration the scene has. That is not a communications shortcut. It is an inhalation dose.
Skin absorption — pinholes are not cosmetic
Intact skin is a barrier. It is not a vault. Lipid-soluble chemicals dissolve in skin oils and cross. The classic technician list is not trivia:
- Pesticides, especially organophosphates and many agricultural concentrates, are built to enter living tissue.
- Phenol (carbolic acid) is absorbed through intact skin and can produce systemic toxicity (central nervous system and cardiac effects) with burns that look deceptively modest at first.
- Hydrofluoric acid (HF) is both a corrosive and a systemic fluoride poison. Pain can be delayed, especially with dilute solutions, while fluoride binds calcium.
- Nerve agents (and related organophosphate military and industrial cousins) are dermal threats, which is why vapor-protective ensembles and tape discipline exist for those entries.
OSHA’s permissible exposure limits (PELs) in 1910 Subpart Z sometimes carry a [skin] notation. That notation means dermal absorption can add a significant dose to whatever you inhale. It is not a fashion footnote. A pinhole in a glove on a phenol or HF job is an exposure pathway, not a laundry problem.
CPC is the dermal control: compatible material, intact seams, correct glove chemical, and contact time short enough that permeation does not win. Chapter 5.3 owns permeation science. This chapter owns the why: skin is a route, so clothing is toxicology equipment.
Ingestion — rehab can poison you without a leak
Adult technicians rarely drink the product on purpose. They ingest residue:
- Outer gloves handle a bottle, then the inner fingers touch a sandwich.
- Someone “just wets their lips” in the warm zone.
- Chewing tobacco or gum in CPC.
- Off-gassing of contaminated suits in the rehabilitation area — vapors leaving dirty CPC and putting an inhalation and ingestion problem into the rest area you thought was clean.
The control is boring and non-negotiable: technical decontamination before rehab, no eating or drinking with contaminated hands, bottles and radios that never wear outer gloves, and dirty CPC that does not hang over the cooler. Ingestion is a hygiene failure more often than a product-control failure.
Injection and ocular — small holes, large doses
Injection is not only a needle. High-pressure product (hydraulic oil, paint, some process lines) can inject through intact skin at a pinhole and travel along tissue planes. Sharps at clandestine laboratories, jagged metal on a damaged drum, and contaminated trauma all skip the skin barrier. Treat high-pressure injection as a surgical emergency, not as a bandage stop.
Ocular exposure is splash and vapor. The eye is a mucous membrane with rapid local damage from corrosives and, for some chemicals, a path toward systemic uptake. A full-face SCBA facepiece is an eye control as well as a lung control. Lifting the visor to “see the valve better” is an ocular and inhalation decision.
Scenario: pinhole glove versus failed SCBA
Two technicians finish the same pesticide transfer.
Technician A has a pinhole in a glove. The SCBA never lost positive pressure. Product on the outer glove is a dermal problem: organophosphate skin absorption, possible inner-glove contamination, and a decontamination and medical follow-up issue even if the person “feels fine.” The lungs were protected. The skin was not.
Technician B has intact gloves and a failed SCBA facepiece seal in the vapor. That is inhalation at cloud concentration — the most common occupational route, the fastest dose, and the reason the buddy and the safety officer exist. Washing Technician B’s gloves does not undo the lung dose. Giving Technician A a new cylinder does not undo the pinhole.
If you remember one sentence: name the route, then pick the barrier — respirator, CPC, decon/hygiene, puncture protection, or eye protection — because a pinhole and a failed SCBA are different toxicology events.
Which route of exposure is the most common occupational pathway for hazardous materials technicians, and which control is matched to it?
A technician completing a phenol transfer discovers a pinhole in a butyl glove. Another technician on the same entry loses the SCBA facepiece seal in the vapor. Which statement is toxicologically correct?
Which practice best controls the ingestion route during a technician operation?