4.2 ERG Green Table and Toxic Inhalation Hazards (TIH)

4.2 ERG Green Table and Toxic Inhalation Hazards (TIH)

The Green-bordered pages of the Emergency Response Guidebook (ERG) contain critical protective action distances for materials that pose a Toxic Inhalation Hazard (TIH). These pages are divided into three tables: Table 1 (Initial Isolation and Protective Action Distances), Table 2 (Water-Reactive Materials Producing Toxic Gases), and Table 3 (Initial Isolation and Protective Action Distances for Six Common TIH Materials). A TIH is defined as a gas or volatile liquid that is highly toxic when inhaled, posing a severe threat to human life and health even in low concentrations. Examples include chlorine, anhydrous ammonia, sulfur dioxide, hydrogen chloride, phosgene, and chemical warfare agents.

The Operational Rule for Green-Highlighted Entries

When a responder identifies a material in the Yellow or Blue pages that is highlighted in green, they must follow a specific operational rule:

1. Spill only (No Fire): Bypass the isolation and evacuation distances listed in the Orange pages and go directly to Table 1 of the Green pages.
2. Spill with Fire: If a green-highlighted material is involved in a fire, or if its container is exposed to fire, the situation presents both a toxicity hazard and a physical explosion/thermal hazard. The responder must check the "Evacuation" sub-section under the Public Safety section in the Orange Guide (which typically mandates a 1/2 mile or 1 mile evacuation zone for bulk containers) and compare it with the distances in the Green pages (Table 1). The responder must implement whichever distance is larger.

Table 1: Initial Isolation and Protective Action Distances

Table 1 is organized numerically by the material's 4-digit UN ID number and lists two primary safety zones:

1. Initial Isolation Zone

The Initial Isolation Zone is a circular area immediately surrounding the spill source where all personnel, including first responders without specialized chemical protective clothing, must be evacuated in all directions. Within this zone, chemical concentrations are likely to be immediately dangerous to life and health. Table 1 lists this distance as a radius in both feet and meters. For instance, a small spill of chlorine (UN 1017) has an initial isolation distance of 100 feet (30 meters), while a large spill has a distance of 500 feet (150 meters).

2. Protective Action Zone

The Protective Action Zone is a downwind, wedge-shaped area where chemical vapors are expected to disperse and pose a health threat to the public. Within this zone, responders must take protective actions, which include either evacuating the public or instructing them to shelter in place. This zone is defined by a downwind distance in miles and kilometers. The width of the zone is equal to the downwind distance, centered on the wind direction.

Small Spills vs. Large Spills

The ERG distinguishes between small and large spills based on the volume of the release and the container type:

• Small Spill: A release from a single small container, such as a package, cylinder, or drum, with a capacity of 55 gallons (208 liters) or less.
• Large Spill: A release from a bulk container, such as a cargo tank, rail tank car, ISO tank, or multiple small containers leaking simultaneously, with a capacity of greater than 55 gallons (208 liters).

Responders must accurately assess the container size. Consulting the small spill column for a leaking 10,000-gallon cargo tank is a critical error that will leave responders and the public exposed to lethal concentrations of toxic gas.

Day vs. Night Protective Action Distances

One of the most important concepts for first responders—and a frequent focus of certification exams—is the difference between daytime and nighttime protective action distances:

• Daytime Distances: During the day, solar radiation heats the Earth's surface, causing thermal convective currents and atmospheric turbulence. This causes air near the ground to rise, carrying toxic gases upward where they mix and disperse rapidly into the upper atmosphere. Consequently, daytime protective action distances are relatively shorter.
• Nighttime Distances: At night, the ground cools rapidly, creating a stable atmosphere. In many cases, a temperature inversion occurs, where a layer of warm air traps cooler air near the surface. This stable air acts as a physical lid, preventing the vertical dispersion of toxic gases. The vapor cloud remains concentrated and hugs the ground, allowing the wind to carry a highly toxic plume over long distances with minimal dilution. As a result, nighttime protective action distances are often three to ten times larger than daytime distances for the same chemical and spill volume.

Table 2: Water-Reactive Materials Producing TIH Gases

Table 2 lists materials alphabetically by chemical name that, when spilled into water, undergo a rapid chemical reaction that generates one or more Toxic Inhalation Hazard (TIH) gases. The table details:

1. The name of the spilled material.
2. Its 4-digit UN ID number.
3. The specific TIH gas or gases produced by the reaction (e.g., hydrogen cyanide, phosphine, hydrogen sulfide).

If a water-reactive material is spilled on land and does not contact water, Table 2 does not apply, and the responder uses the standard Orange Guide or Table 1 (if the material is also highlighted in green on land). However, if water is present, the responder must look up the material in Table 2, identify the toxic gas produced, and then use Table 1 to determine the protective distances for that specific TIH gas.

Table 3: Six Common TIH Materials

Table 3 provides initial isolation and protective action distances for six of the most common industrial TIH materials, categorized by container type and wind speed:

• Anhydrous ammonia (UN 1005)
• Chlorine (UN 1017)
• Ethylene oxide (UN 1040)
• Hydrogen chloride (UN 1050)
• Hydrogen fluoride (UN 1052)
• Sulfur dioxide (UN 1079)

Because wind speed plays a major role in how quickly a gas plume travels and dilutes, Table 3 divides protective action distances into three wind speed categories (low, moderate, and high) for various common transport containers. This allows responders to refine their safety zones based on real-time local weather observations.