8.3 Evidence Preservation, Sampling & Radiological Response

8.3 Evidence Preservation, Sampling & Radiological Response

Crime Scene Preservation at Hazmat Incidents

When a hazardous materials incident results from an intentional act, criminal activity, or illicit CBRN (Chemical, Biological, Radiological, Nuclear) release, the incident site becomes an active crime scene. Responders carrying out NFPA 470 Chapter 9 mission-specific competencies must balance life safety and hazard mitigation with Evidence Preservation.

Preservation Guidelines for Responders

• Minimize Scene Disturbance: Avoid moving structural elements, chemical containers, or physical items unless necessary for life safety or suppression.
• Document Initial Scene State: Note container positions, valve orientations, control panel settings, footprints, tire tracks, and unusual odors prior to tactical actions.
• Establish Scene Perimeter: Expand the Hot Zone security perimeter to encompass all potential physical evidence areas and prevent unauthorized entry by onlookers or non-essential personnel.
• Coordinate with Law Enforcement: Coordinate entry tactics with law enforcement investigators to prevent destruction of fingerprints, DNA, or trace chemical residue.

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Chain of Custody Protocol & Evidence Packaging

Chain of Custody is the unbroken, chronological documentation that records the sequence of custody, control, transfer, analysis, and disposition of physical or electronic evidence. Without a verified chain of custody, collected evidence is inadmissible in legal proceedings.

Chain of Custody Key Information

• Unique Evidence Tracking ID / Case Number.
• Exact location of discovery (including GPS coordinates, room designation, or spatial coordinates).
• Date and precise timestamp of collection.
• Full name, agency, rank, and signature of the sampler.
• Item description (volume, physical state, container type).
• Signatures of all individuals transferring and receiving the evidence during transport to accredited laboratories.

Evidence Packaging Standards

• Primary Container: Must be chemically compatible with the sample (e.g., borosilicate glass jars with Teflon-lined caps for unknown organic solvents; fluorinated HDPE bottles for corrosive liquids).
• Secondary Container: Shock-resistant outer container holding sorbent material to absorb liquids in case of primary container leakage.
• Tamper-Evident Seals: Applied across container closures such that any attempt to open or alter the sample breaks the seal tape and leaves clear visual evidence.

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Sampling Execution & Clean-Glove/Dirty-Glove Technique

To collect valid liquid, solid, or surface wipe samples from a hazardous incident scene without introducing outside contamination, responders employ the Clean-Glove / Dirty-Glove Technique. This protocol requires a two-person entry team.

Protocol Steps

1. Dirty Sampler Role: Touches contaminated surfaces, operates sampling scoops/pipettes, and transfers raw media into the primary specimen container held by the Clean Sampler.
2. Clean Sampler Role: Opens clean inner packaging, holds the exterior of the sample container without touching the contaminated site, seals the container, applies tamper-evident tape, and completes the custody log.
3. Outer Decontamination: The exterior of the sealed sample container is wiped down with an approved chemical decon wipe prior to placement in secondary packaging.

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Radiological Monitoring Instrumentation

Mission-specific responders assigned to radiological incidents must monitor ionizing radiation levels, identify radiation types, and verify scene safety parameters.

Radiation Types & Physical Shielding

• Alpha ($\alpha$) Particles: Heavy, positively charged helium nuclei. Low penetration power; stopped by a single sheet of paper or human skin. Primary hazard is internal contamination if inhaled or ingested.
• Beta ($\beta$) Particles: High-speed electrons. Moderate penetration; stopped by plastic, aluminum sheeting, or heavy clothing. Can cause skin burns and eye damage.
• Gamma ($\gamma$) Rays & X-Rays: High-energy electromagnetic waves. High penetration power; requires dense shielding like lead, steel, or thick concrete.
• Neutron Radiation: Uncharged nuclear particles emitted during fission reactions. Extremely penetrating; requires hydrogen-rich shielding materials like water, paraffin wax, or polyethylene.

Detection Instruments

• Geiger-Müller (GM) Survey Meters: Highly sensitive instruments used to detect low levels of alpha, beta, and gamma radiation. Measures counts per minute (CPM). Excellent for locating lost sources or surface contamination.
• Ionization Chambers: Measure high dose rates of gamma and X-ray radiation accurately in milliRem per hour (mR/hr) or Rem per hour (R/hr). Used for assessing entry risk in high-radiation fields.
• Personal Dosimeters: Electronic Personal Dosimeters (EPD) or Optically Stimulated Luminescence (OSL) badges worn by responders to measure cumulative personal radiation dose.

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ALARA Principles & Radiation Safety Physics

Radiation safety operations follow the ALARA Principle (As Low As Reasonably Achievable), minimizing total radiation exposure through three primary controls: Time, Distance, and Shielding.

The Three Pillars of ALARA

1. Time: Minimize exposure duration. Calculate Stay Time before entering a radiation field: $\text{Stay Time (Hours)} = \frac{\text{Allowed Exposure Dose Limit (mRem)}}{\text{Dose Rate at Incident Location (mRem/hr)}}$
2. Distance: Maximize distance from the radiation source. Radiation intensity follows the Inverse Square Law: $I_1 \cdot (d_1)^2 = I_2 \cdot (d_2)^2$ Doubling the distance from a point source reduces the exposure rate to one-fourth ($\frac{1}{4}$) of the original value.
3. Shielding: Position dense materials between responders and the source to absorb radiation energy.

EPA Worker Protection Dose Limits

Emergency responder exposure guidelines established by the EPA during radiological emergencies: