3.1 Site Characterization Phases & Risk Assessment

Introduction to Site Characterization

Site characterization is a continuous process mandated by OSHA under 29 CFR 1910.120(c). Its primary purpose is to identify specific site hazards and determine the appropriate safety and health control procedures needed to protect workers from identified hazards. The characterization process ensures that all potential risks—whether chemical, biological, radiological, or physical—are properly evaluated before personnel enter the site and continuously monitored while work is being conducted. The site characterization framework consists of three distinct phases: Phase 1 (Off-site Preliminary Assessment), Phase 2 (Initial On-site Entry), and Phase 3 (Ongoing Monitoring and Hazard Reassessment).

Phase 1: Off-Site Preliminary Assessment

The off-site preliminary assessment is conducted before any personnel enter the site. The goal is to gather as much information as possible without exposing workers to unknown hazards. This phase relies on non-invasive data collection techniques and historical research to build an initial profile of the site.

Information Gathering Techniques

During Phase 1, environmental professionals utilize several resources to compile a comprehensive site history. These include:

• Historical Records: Reviewing past property deeds, tax records, and previous environmental assessments can reveal the historical uses of the site. For example, a site that was once a dry cleaner or an industrial manufacturing facility is likely to have soil and groundwater contamination from chlorinated solvents or heavy metals.
• Aerial Photos: Historical aerial photography can show the evolution of the site over time. It can reveal the location of former structures, waste pits, lagoons, or stressed vegetation that may indicate the presence of buried hazardous materials.
• Manifests and Shipping Records: Reviewing hazardous waste manifests provides direct evidence of the types and quantities of chemicals that were generated, stored, or disposed of at the facility.
• Interviews: Conducting interviews with former employees, neighbors, or local officials can provide invaluable anecdotal evidence about past practices, spills, or unrecorded waste disposal activities.
• Perimeter Reconnaissance: Observing the site from a safe distance outside the property boundaries. This involves looking for warning signs such as placards, labels, unusual odors, visible vapor clouds, or dead vegetation. Monitors like binoculars and long-range cameras are frequently used.

Phase 2: Initial On-Site Entry

Once the off-site assessment is complete and an initial site safety plan is drafted, Phase 2 begins. This phase involves the first physical entry onto the site by trained personnel to verify the findings of Phase 1 and identify hazards that could not be detected from the perimeter.

Mandatory Safety Protocols

Because the exact nature and concentration of hazards are not yet fully known, OSHA mandates stringent safety protocols for initial entry:

• Minimum Protection Levels: Know both the rule and its source. The regulation, 1910.120(c)(5)(i), is performance-based: the entry ensemble must be selected from the results of the preliminary evaluation and must hold exposure below the permissible exposure limits and published exposure levels for known or suspected substances, while also protecting against the other hazards identified. 1910.120(c)(5)(ii) adds a hard equipment rule: if positive-pressure SCBA is not part of the ensemble and respiratory protection is warranted, each employee must carry an escape SCBA of at least five minutes' duration during initial entry. The familiar "Level B is the minimum for initial entry" rule comes from EPA/NIOSH guidance (the Occupational Safety and Health Guidance Manual for Hazardous Waste Site Activities and EPA's Standard Operating Safety Guides), reinforced by non-mandatory Appendix B to 1910.120, which recommends Level B where incompletely identified vapors are detected but are not suspected of being skin-absorbable. Level A is indicated instead when the unknown hazards may be absorbed through intact skin — and 1910.120(g)(4)(iv) makes totally-encapsulating suits mandatory where skin absorption could cause immediate death, immediate serious illness or injury, or impair the ability to escape.
• Buddy System: No individual is ever allowed to enter a hazardous waste site alone. The buddy system ensures that workers operate in pairs, keeping each other in visual or voice contact at all times to provide immediate assistance if an emergency occurs.
• Backup Team: A fully equipped backup team must remain on standby outside the hot zone, ready to initiate a rescue if the entry team encounters trouble. The backup team must be dressed in the same level of PPE as the entry team or one level lower, ready to don respiratory protection instantly.
• Entry Team Sizing: The entry team should consist of the minimum number of personnel necessary to perform the required tasks safely and efficiently. Typically, an entry team consists of two to three individuals.

On-Site Activities

During the initial entry, the team conducts a visual inspection and utilizes direct-reading instruments to monitor the atmosphere for immediate dangers to life and health (IDLH) conditions, such as oxygen deficiency, explosive atmospheres, or toxic gas concentrations. They will also look for indicators such as bulging drums, leaking containers, or open electrical panels.

Phase 3: Ongoing Monitoring and Continuous Hazard Reassessment

Site characterization does not end after the initial entry. As site operations commence and progress, conditions can change rapidly. Phase 3 focuses on continuous monitoring and reassessment of hazards throughout the project's lifecycle.

Dynamic Risk Environment

Activities such as excavation, drilling, or drum handling can release previously trapped gases or vapors, altering the atmospheric conditions. Therefore, continuous air monitoring is essential to ensure that the chosen PPE remains adequate and that action levels are not exceeded. If conditions degrade, work must be paused, and the site safety plan must be updated to reflect the new hazard profile.

Comprehensive Risk Assessment

A critical component of all three phases is the execution of a comprehensive risk assessment. This process identifies all potential hazards and evaluates the risk they pose to workers.

Identifying Hazards

• Biological Hazards: Exposure to medical waste, sewage, poisonous plants, insects (e.g., ticks carrying Lyme disease), or dangerous animals.
• Radiological Hazards: Exposure to ionizing radiation from medical equipment, industrial gauges, or naturally occurring radioactive materials (NORM).
• Electrical Hazards: Risks posed by overhead power lines, buried cables, or improperly grounded equipment, especially in wet environments.
• Physical Hazards: Dangers such as extreme temperatures (heat stress or cold stress), noise, uneven terrain, heavy machinery operations, and structural collapse.

Risk Matrix Methodology

A risk matrix is a fundamental tool used to evaluate hazards based on two main criteria: the probability (likelihood) of an incident occurring and the severity (consequence) if it does occur. By plotting these variables on a matrix, safety professionals can categorize risks as low, medium, high, or critical. This prioritization dictates the level of control measures required, ensuring that the most significant threats are addressed first and most rigorously.

Phase-by-Phase Operational Table