# Protective Action Decision Guidance

- **operation:** document
- **citation:** ERG 2024, Protective Action Decision Guidance
- **title:** Protective Action Decision Guidance
- **source type:** guidance
- **agency:** U.S. DOT / Transport Canada / SICT
- **status:** guidance
- **official:** true
- **published on:** 2024-04-04
- **effective on:** Not available
- **summary:** Official ERG2024 protective action decision guidance guidance, pages 282-289.
- **machine formats:** - **json:** https://regulus.evalyn.ai/document/phmsa-erg-2024-green-table-introduction.json
- **markdown:** https://regulus.evalyn.ai/document/phmsa-erg-2024-green-table-introduction.md
- **app url:** https://regulus.evalyn.ai/document/phmsa-erg-2024-green-table-introduction
- **source url:** https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/2024-04/ERG2024-Eng-Web-a.pdf#page=282
**body:**

INTRODUCTION TO GREEN TABLES
TABLE 1 - INITIAL ISOLATION AND PROTECTIVE ACTION DISTANCES
This table suggests distances useful to protect people from vapors/gases resulting from
spills involving:
•
materials that are considered toxic by inhalation (TIH) (PIH in the US)
•
materials which produce toxic gases upon contact with water
This table provides first responders with initial guidance until technically qualified emergency
response personnel are available. For each material, first responders will find distances for
the following zones:
•
The Initial Isolation Zone defines an area surrounding the incident in which
people may be exposed to dangerous (upwind) and life-threatening (downwind)
concentrations of material.
•
The Protective Action Zone defines an area downwind from the incident in which
people may become incapacitated and unable to take protective action and/or incur
serious or irreversible health effects. Table 1 provides specific guidance for small
and large spills occurring day or night.
Adjusting distances for a specific incident involves many interdependent variables. These
adjustments should only be made by technically qualified personnel. For this reason, no
precise guidance can be provided in this document to aid in adjusting the table distances;
however, general guidance follows.
Factors that May Change the Protective Action Distances
Fire
In the orange section, under EVACUATION – Fire, the evacuation distance required to
protect against fragmentation hazard of a large container is clearly indicated. If involved in a
fire, the toxic hazard may be less dangerous than the fire or explosion hazard.
In these cases, the fire hazard distance should be used as an isolation distance and Table
1 should be used to protect downwind for residual material release.
Worst-case scenario: terrorism, sabotage or catastrophic accident
Initial isolation and protective action distances are derived from historical data on
transportation incidents and the use of statistical models. For worst-case scenarios involving
the instantaneous release of the entire contents of a package (e.g., as a result of terrorism,
sabotage or catastrophic accident), the distances may increase substantially.
For such events, doubling the initial isolation and protective action distances is appropriate
in absence of other information.
When more than one large package is leaking
If more than one rail tank car, highway tank, tank or large cylinder, containing TIH materials
is leaking, large spill distances may need to be increased.
Page 280

Other factors that can increase the protective action distance:
•
•
•
•
•
•
If a material has a protective action distance of 11.0+ km (7.0+ miles), the actual
distance can be larger in certain atmospheric conditions.
If the material’s vapor plume is channeled in a valley or between many tall
buildings, protective action distances may be larger than shown due to less mixing
of the plume with the atmosphere.
If there is a daytime spill in a region with known strong temperature inversions
or snow cover, or it occurs near sunset, this may require an increase of the
protective action distance because airborne contaminants mix and disperse more
slowly and may travel much farther downwind.
› In such cases, the nighttime protective action distances may be more
›
appropriate.
If the temperature of the liquid spill or the outdoor temperature exceeds 30°C
(86°F), the protective action distance may be larger.
Water-reactive materials
Materials that react with water to produce large amounts of toxic gases are included in Table
1. Some of these materials have 2 entries in Table 1. They are identified by (when spilled
on land) since they are TIH products and (when spilled in water) because they produce
additional toxic gases when spilled in water.
Choose the larger protective action distance if:
it is not clear whether the spill is on land or in water
the spill occurs both on land and in water
TABLE 2 - WATER-REACTIVE MATERIALS WHICH PRODUCE TOXIC GASES
This table lists materials which produce large amounts of Toxic Inhalation Hazard gases
(TIH) when spilled in water as well as the TIH gases that are produced.
NOTE: The produced TIH gases indicated in Table 2 are for information purposes only.
In Table 1, the initial isolation and protective action distances have already taken into
consideration the produced TIH gas.
When a water-reactive TIH-producing material is spilled into a river or stream, the source of
the toxic gas may flow downstream for a great distance.
Page 281

TABLE 3 - INITIAL ISOLATION AND PROTECTIVE ACTION DISTANCES FOR LARGE
SPILLS FOR DIFFERENT QUANTITIES OF SIX COMMON TIH (PIH IN THE US) GASES
This table lists materials that may be more commonly encountered. These materials are:
•
UN1005 - Ammonia, anhydrous
•
UN1017 - Chlorine
•
UN1040 - Ethylene oxide and UN1040 - Ethylene oxide with nitrogen
•
UN1050 - Hydrogen chloride, anhydrous and UN2186 - Hydrogen chloride,
refrigerated liquid
•
UN1052 - Hydrogen fluoride, anhydrous
•
UN1079 - Sulfur dioxide/Sulphur dioxide
This table provides initial isolation and protective action distances for large spills (more than
208 liters or 55 US gallons):
•
involving different container types (therefore different volume capacities)
•
for daytime and nighttime situations
•
for different wind speeds (low, moderate and high)
Page 282

PROTECTIVE ACTIONS
Protective actions are the steps taken to preserve the health and safety of emergency
responders and the public during an incident involving releases of hazardous materials/
dangerous goods.
Table 1 - Initial Isolation and Protective Action Distances (green section) predicts the size
of the area that could be affected by a cloud of toxic gas. People in this area should be
evacuated and/or sheltered-in-place inside buildings.
Isolate hazard area and deny entry means to keep everybody away from the area if they are
not directly involved in emergency response operations. Unprotected emergency responders
should not be allowed to enter the isolation zone.
This "isolation" task is done to establish control over the area of operations. This is the first
step for any protective actions that may follow.
Evacuate means to move all people from a threatened area to a safer place. To perform an
evacuation, there must be enough time for people to be warned, get ready, and leave an
area. If there is enough time, evacuation is the best protective action.
Begin evacuating people nearby and those who are outdoors in direct view of the scene.
When additional help arrives, expand the area to be evacuated downwind and crosswind to
at least the extent recommended in this guidebook.
Even after people move to the distances recommended, they may not be completely safe
from harm. They should not be permitted to gather at such distances. Send evacuees to a
definite place, by a specific route, far enough away so they will not have to relocate again
if the wind shifts.
Shelter-in-place means people should seek shelter inside a building and remain inside
until the danger passes. It is vital for first responders to maintain communications with
sheltered-in-place people so that they are advised about changing conditions.
Sheltering-in-place is used either when:
•
evacuating the public would cause greater risk than staying where they are
•
an evacuation cannot be safely performed
Direct the people inside to:
•
close all doors and windows
•
shut off all ventilating, heating and cooling systems
•
stay far from windows to avoid shattered glass and projectile metal fragments in
the event of a fire and/or explosion
•
seal cracks around doors, windows and vents with duct tape or wet cloths
•
tune in to local media, and remain inside until told it is safe to leave by first
responders or emergency response authorities
•
breathe through a wet cloth until an all clear has been communicated
Vehicles can offer some protection for a short period if the windows are closed and the
ventilation systems are shut off. Vehicles are not nearly as effective as buildings for in-place
protection.
Page 283

PROTECTIVE ACTION DECISION FACTORS TO CONSIDER
The choice of protective actions for a given situation depends on a number of factors. For
some cases, evacuation may be the best option; in others, sheltering-in-place may be the
best course. Sometimes, these two actions may be used in combination. In any emergency,
officials need to quickly give the public instructions. The public will need continuing information
and instructions while being evacuated or sheltered-in-place.
Proper evaluation of the factors listed below will determine the effectiveness of evacuation or
in-place protection (shelter-in-place). The importance of these factors can vary with emergency
conditions. In specific emergencies, other factors may need to be identified and considered as
well. This list indicates what kind of information may be needed to make the initial decision.
The hazardous materials/dangerous goods:
•
degree of health hazard
•
chemical and physical properties
•
amount involved
•
containment/control of release
•
rate of vapor movement
The population threatened:
•
location
•
number of people
•
time available to evacuate or shelter-in-place
•
ability to control evacuation or shelter-in-place
•
building types and availability
•
special institutions or populations, e.g., nursing homes, hospitals, prisons
The weather conditions:
•
effect on vapor and cloud movement
•
potential for change
•
effect on evacuation or shelter-in-place
NOTE: Every hazardous materials/dangerous goods incident is different. Each will have
special problems and concerns. Actions to protect the public must be carefully selected.
This section can help with initial decisions on how to protect the public. Officials must
continue to gather information and monitor the situation until the threat is removed.
Page 284

The following table can help to decide if evacuation or sheltering-in-place
is the best option:
Consider Evacuation: Consider Sheltering-in-place:
Vapors are flammable. Vapors are toxic, and people are likely
to be exposed by evacuating.
Buildings cannot be closed tightly. Buildings can be quickly sealed by
closing all windows and ventilation
systems, if applicable.
The vapors are continuously generated
and will hug the ground, or it will take a
long time for the vapors to clear the area.
The vapors will quickly rise in the air
column or rapidly dissipate.
For anyone outdoors. For anyone already indoors.
There are few people to evacuate. There are too many people to evacuate
for current available resources.
The threat seems stable but long-
lasting.
Circumstances are changing too quickly
to evacuate safely.
Page 285

BACKGROUND ON TABLE 1 – INITIAL ISOLATION
AND PROTECTIVE ACTION DISTANCES
Initial isolation and protective action distances in this guidebook were determined for small
and large spills occurring during day or night. The overall analysis, statistical in nature, was
conducted using:
•
state-of-the-art emission rate and dispersion models
•
statistical release data from the U.S. Department of Transportation (DOT)
Hazardous Materials Information System (HMIS) database
•
meteorological observations from more than 120 locations in the United States,
Canada, and Mexico
•
the most current toxicological exposure guidelines
For each chemical, thousands of hypothetical releases were modeled to account for the statistical
variance in both release amount and atmospheric conditions. Based on this statistical sample,
they selected the 90th percentile protective action distance for each chemical and category to
appear in the table. A brief description of the analysis is provided below.
A detailed report outlining the methodology and data used to generate the initial isolation and
protective action distances may be obtained from the U.S. DOT, Pipeline and Hazardous
Materials Safety Administration (PHMSA).
DESCRIPTION OF THE ANALYSIS
Release amounts and emission rates into the atmosphere were statistically modeled
based on:
•
data from the U.S. DOT HMIS database
•
container types and sizes authorized for transport as specified in 49 CFR §172.101
and Part 173
•
physical properties of the individual materials
•
atmospheric data from a historical database
For liquefied gases, which can flash to form both a vapor/aerosol mixture and an evaporating
pool, the emission model calculated one or both of:
•
the release of vapor due to evaporation of pools on the ground
•
direct release of vapors from the container
The emission model also calculated the emission of toxic vapor by-products generated from
spilling water-reactive materials in water.
Small spills involve 208 liters (55 US gallons) or less.
Large spills involve greater quantities.
Page 286

Downwind dispersion of the vapor was estimated for each case modeled. Using a database
containing hourly meteorological data from 120 American, Canadian, and Mexican cities,
the atmospheric parameters affecting the dispersion and the emission rate were selected.
The dispersion calculation accounted for both the:
•
time-dependent emission rate from the source
•
density of the vapor plume (i.e., heavy gas effects)
Since atmospheric mixing is less effective at dispersing vapor plumes during nighttime, day
and night were separated in the analysis.
In the table:
•
day refers to time periods after sunrise and before sunset
•
night includes all hours between sunset and sunrise
Toxicological short-term exposure guidelines for the materials were applied to determine
the downwind distance to which people may:
•
become incapacitated and unable to take protective action
•
incur serious health effects after a single, or rare, exposure
When available, toxicological exposure guidelines were chosen from AEGL-2 or ERPG-2
emergency response guidelines. AEGL-2 values were the first choice.
For materials without AEGL-2 or ERPG-2 values, emergency response guidelines were
estimated based on lethal concentration limits derived from animal-based-studies. This
approach was recommended by an independent panel of toxicological experts from industry
and academia.
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