Contamination Control: Entry, Exit, and Decontamination Procedures

Why Contamination Control Matters

In a nuclear plant, radioactive contamination means loose radioactive material that has spread to a surface, clothing, equipment, or the human body where it does not belong. Even small amounts of contamination on skin or clothing can deliver an unplanned radiation dose over time and can spread that material to clean areas of the plant or to the public. Contamination control is therefore one of the most fundamental radiation protection disciplines, and every nuclear worker — licensed or not — must perform entry and exit procedures correctly every single time.

The Radiological Controlled Area (RCA) is the boundary within which contamination hazards exist. You must treat every surface inside the RCA as potentially contaminated until monitoring proves otherwise.

Anti-Contamination Clothing

Anti-contamination clothing, universally called anti-C clothing, is not a radiation shield. It does not stop gamma rays or neutrons. Its purpose is to keep radioactive particles off your skin and personal clothing so that when you leave the RCA you leave the contamination behind. Typical anti-C ensembles include:

• Coveralls — full-body coverage, usually Tyvek or cotton
• Boot covers — inner and outer, covering footwear to the ankle or calf
• Gloves — inner (cotton or latex) and outer (heavier latex or nitrile)
• Hood — covers hair and ears, leaving only the face exposed
• Respirator — added when airborne contamination is possible (half-face or full-face air-purifying, or supplied air, depending on the radiological hazard)

All anti-C is single-use or laundered under controlled conditions. Never take anti-C clothing outside the plant's radiological waste or laundry stream.

The Step-Off Pad

The step-off pad is a clean mat placed at the boundary of a contaminated area. It marks the exact point where your anti-C clothing must be removed before your foot touches the clean floor. One side of the pad faces the contaminated area; the other faces the clean area. You must step off the pad toward clean only once your feet are free of contaminated boot covers. Think of the pad as a physical enforcement of the contamination boundary.

Donning Sequence

Don anti-C in a clean area just outside the RCA entry point. The correct order prevents you from contaminating the outer layers with your hands while putting on inner layers:

1. Inner boot covers over personal shoes

2. Inner gloves (cotton or thin latex)

3. Coveralls — zip fully; tuck sleeves over inner gloves

4. Hood — seat snugly; tuck into coverall collar

5. Outer boot covers — tape to coverall leg if required by procedure

6. Outer gloves — pull cuff over coverall sleeve

7. Respirator (when required) — seal-check before entering

Your partner verifies each step against the written procedure. Never skip the buddy check.

Doffing Sequence at the Step-Off Pad

Doffing — removing anti-C at the exit — is the highest-risk moment for self-contamination. The roll-away technique keeps potentially contaminated outer surfaces folded inward so they never touch clean skin or clothing:

1. While still on the contaminated side, remove the respirator (if worn) and place it in a designated bag or waste container.

2. Remove outer gloves by peeling from the wrist, rolling contaminated side inward; dispose in waste container.

3. Remove outer boot covers one at a time, lifting each foot and stepping it directly onto the step-off pad — never back to the contaminated floor.

4. Remove coveralls and hood together by rolling downward from the shoulders, keeping the contaminated outside rolled inward; avoid shaking. Step out of coveralls onto the pad.

5. Remove inner boot covers and step off the pad to the clean side with bare (or personal shoe) feet.

6. Remove inner gloves by peeling, rolling contaminated side inward.

7. Place all waste in the radiological waste bag or container at the pad.

At every step, keep your hands away from your face and avoid touching your personal clothing with outer layers.

Self-Frisk Procedure

After doffing, proceed immediately to the frisker station and perform a self-frisk with a Geiger-Mueller (GM) thin-window detector:

• Hold the probe approximately 1 cm (about half an inch) from the surface being scanned — close enough to detect alpha and low-energy beta, but not dragging on skin.
• Move the probe slowly: approximately 5 cm per second or slower.
• Scan hands and wrists thoroughly (most likely contamination site from glove removal).
• Scan the bottoms and tops of feet and ankles.
• Scan the face and neck (forehead, around eyes, chin).
• Listen for count-rate changes; watch the meter display.
• If the meter alarms or shows a count rate significantly above background, stop and notify the Radiation Protection (RP) technician immediately. Do not leave the frisker station.

If contamination is found on skin, RP staff will direct decontamination — typically gentle washing with lukewarm water and mild soap, repeated until count rates return to background or an acceptable release level. Do not scrub aggressively; this opens pores and can drive contamination in.

Key Safety Rules

• Always follow the written site procedure. Steps vary slightly between plants; the written procedure controls.
• Never rush doffing. Haste is the leading cause of self-contamination during exit.
• Buddy checks are not optional. A second set of eyes catches missed areas.
• Report all detected contamination to RP staff, even if the level seems low.
• Anti-C clothing provides no dose protection against penetrating radiation; time, distance, and shielding remain your dose controls inside the RCA.