{"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":null,"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\nTABLE 1 - INITIAL ISOLATION AND PROTECTIVE ACTION DISTANCES\nThis table suggests distances useful to protect people from vapors/gases resulting from\nspills involving:\n•\nmaterials that are considered toxic by inhalation (TIH) (PIH in the US)\n•\nmaterials which produce toxic gases upon contact with water\nThis table provides first responders with initial guidance until technically qualified emergency\nresponse personnel are available. For each material, first responders will find distances for\nthe following zones:\n•\nThe Initial Isolation Zone defines an area surrounding the incident in which\npeople may be exposed to dangerous (upwind) and life-threatening (downwind)\nconcentrations of material.\n•\nThe Protective Action Zone defines an area downwind from the incident in which\npeople may become incapacitated and unable to take protective action and/or incur\nserious or irreversible health effects. Table 1 provides specific guidance for small\nand large spills occurring day or night.\nAdjusting distances for a specific incident involves many interdependent variables. These\nadjustments should only be made by technically qualified personnel. For this reason, no\nprecise guidance can be provided in this document to aid in adjusting the table distances;\nhowever, general guidance follows.\nFactors that May Change the Protective Action Distances\nFire\nIn the orange section, under EVACUATION – Fire, the evacuation distance required to\nprotect against fragmentation hazard of a large container is clearly indicated. If involved in a\nfire, the toxic hazard may be less dangerous than the fire or explosion hazard.\nIn these cases, the fire hazard distance should be used as an isolation distance and Table\n1 should be used to protect downwind for residual material release.\nWorst-case scenario: terrorism, sabotage or catastrophic accident\nInitial isolation and protective action distances are derived from historical data on\ntransportation incidents and the use of statistical models. For worst-case scenarios involving\nthe instantaneous release of the entire contents of a package (e.g., as a result of terrorism,\nsabotage or catastrophic accident), the distances may increase substantially.\nFor such events, doubling the initial isolation and protective action distances is appropriate\nin absence of other information.\nWhen more than one large package is leaking\nIf more than one rail tank car, highway tank, tank or large cylinder, containing TIH materials\nis leaking, large spill distances may need to be increased.\nPage 280\n\nOther factors that can increase the protective action distance:\n•\n•\n•\n•\n•\n•\nIf a material has a protective action distance of 11.0+ km (7.0+ miles), the actual\ndistance can be larger in certain atmospheric conditions.\nIf the material’s vapor plume is channeled in a valley or between many tall\nbuildings, protective action distances may be larger than shown due to less mixing\nof the plume with the atmosphere.\nIf there is a daytime spill in a region with known strong temperature inversions\nor snow cover, or it occurs near sunset, this may require an increase of the\nprotective action distance because airborne contaminants mix and disperse more\nslowly and may travel much farther downwind.\n› In such cases, the nighttime protective action distances may be more\n›\nappropriate.\nIf the temperature of the liquid spill or the outdoor temperature exceeds 30°C\n(86°F), the protective action distance may be larger.\nWater-reactive materials\nMaterials that react with water to produce large amounts of toxic gases are included in Table\n1. Some of these materials have 2 entries in Table 1. They are identified by (when spilled\non land) since they are TIH products and (when spilled in water) because they produce\nadditional toxic gases when spilled in water.\nChoose the larger protective action distance if:\nit is not clear whether the spill is on land or in water\nthe spill occurs both on land and in water\nTABLE 2 - WATER-REACTIVE MATERIALS WHICH PRODUCE TOXIC GASES\nThis table lists materials which produce large amounts of Toxic Inhalation Hazard gases\n(TIH) when spilled in water as well as the TIH gases that are produced.\nNOTE: The produced TIH gases indicated in Table 2 are for information purposes only.\nIn Table 1, the initial isolation and protective action distances have already taken into\nconsideration the produced TIH gas.\nWhen a water-reactive TIH-producing material is spilled into a river or stream, the source of\nthe toxic gas may flow downstream for a great distance.\nPage 281\n\nTABLE 3 - INITIAL ISOLATION AND PROTECTIVE ACTION DISTANCES FOR LARGE\nSPILLS FOR DIFFERENT QUANTITIES OF SIX COMMON TIH (PIH IN THE US) GASES\nThis table lists materials that may be more commonly encountered. These materials are:\n•\nUN1005 - Ammonia, anhydrous\n•\nUN1017 - Chlorine\n•\nUN1040 - Ethylene oxide and UN1040 - Ethylene oxide with nitrogen\n•\nUN1050 - Hydrogen chloride, anhydrous and UN2186 - Hydrogen chloride,\nrefrigerated liquid\n•\nUN1052 - Hydrogen fluoride, anhydrous\n•\nUN1079 - Sulfur dioxide/Sulphur dioxide\nThis table provides initial isolation and protective action distances for large spills (more than\n208 liters or 55 US gallons):\n•\ninvolving different container types (therefore different volume capacities)\n•\nfor daytime and nighttime situations\n•\nfor different wind speeds (low, moderate and high)\nPage 282\n\nPROTECTIVE ACTIONS\nProtective actions are the steps taken to preserve the health and safety of emergency\nresponders and the public during an incident involving releases of hazardous materials/\ndangerous goods.\nTable 1 - Initial Isolation and Protective Action Distances (green section) predicts the size\nof the area that could be affected by a cloud of toxic gas. People in this area should be\nevacuated and/or sheltered-in-place inside buildings.\nIsolate hazard area and deny entry means to keep everybody away from the area if they are\nnot directly involved in emergency response operations. Unprotected emergency responders\nshould not be allowed to enter the isolation zone.\nThis \"isolation\" task is done to establish control over the area of operations. This is the first\nstep for any protective actions that may follow.\nEvacuate means to move all people from a threatened area to a safer place. To perform an\nevacuation, there must be enough time for people to be warned, get ready, and leave an\narea. If there is enough time, evacuation is the best protective action.\nBegin evacuating people nearby and those who are outdoors in direct view of the scene.\nWhen additional help arrives, expand the area to be evacuated downwind and crosswind to\nat least the extent recommended in this guidebook.\nEven after people move to the distances recommended, they may not be completely safe\nfrom harm. They should not be permitted to gather at such distances. Send evacuees to a\ndefinite place, by a specific route, far enough away so they will not have to relocate again\nif the wind shifts.\nShelter-in-place means people should seek shelter inside a building and remain inside\nuntil the danger passes. It is vital for first responders to maintain communications with\nsheltered-in-place people so that they are advised about changing conditions.\nSheltering-in-place is used either when:\n•\nevacuating the public would cause greater risk than staying where they are\n•\nan evacuation cannot be safely performed\nDirect the people inside to:\n•\nclose all doors and windows\n•\nshut off all ventilating, heating and cooling systems\n•\nstay far from windows to avoid shattered glass and projectile metal fragments in\nthe event of a fire and/or explosion\n•\nseal cracks around doors, windows and vents with duct tape or wet cloths\n•\ntune in to local media, and remain inside until told it is safe to leave by first\nresponders or emergency response authorities\n•\nbreathe through a wet cloth until an all clear has been communicated\nVehicles can offer some protection for a short period if the windows are closed and the\nventilation systems are shut off. Vehicles are not nearly as effective as buildings for in-place\nprotection.\nPage 283\n\nPROTECTIVE ACTION DECISION FACTORS TO CONSIDER\nThe choice of protective actions for a given situation depends on a number of factors. For\nsome cases, evacuation may be the best option; in others, sheltering-in-place may be the\nbest course. Sometimes, these two actions may be used in combination. In any emergency,\nofficials need to quickly give the public instructions. The public will need continuing information\nand instructions while being evacuated or sheltered-in-place.\nProper evaluation of the factors listed below will determine the effectiveness of evacuation or\nin-place protection (shelter-in-place). The importance of these factors can vary with emergency\nconditions. In specific emergencies, other factors may need to be identified and considered as\nwell. This list indicates what kind of information may be needed to make the initial decision.\nThe hazardous materials/dangerous goods:\n•\ndegree of health hazard\n•\nchemical and physical properties\n•\namount involved\n•\ncontainment/control of release\n•\nrate of vapor movement\nThe population threatened:\n•\nlocation\n•\nnumber of people\n•\ntime available to evacuate or shelter-in-place\n•\nability to control evacuation or shelter-in-place\n•\nbuilding types and availability\n•\nspecial institutions or populations, e.g., nursing homes, hospitals, prisons\nThe weather conditions:\n•\neffect on vapor and cloud movement\n•\npotential for change\n•\neffect on evacuation or shelter-in-place\nNOTE: Every hazardous materials/dangerous goods incident is different. Each will have\nspecial problems and concerns. Actions to protect the public must be carefully selected.\nThis section can help with initial decisions on how to protect the public. Officials must\ncontinue to gather information and monitor the situation until the threat is removed.\nPage 284\n\nThe following table can help to decide if evacuation or sheltering-in-place\nis the best option:\nConsider Evacuation: Consider Sheltering-in-place:\nVapors are flammable. Vapors are toxic, and people are likely\nto be exposed by evacuating.\nBuildings cannot be closed tightly. Buildings can be quickly sealed by\nclosing all windows and ventilation\nsystems, if applicable.\nThe vapors are continuously generated\nand will hug the ground, or it will take a\nlong time for the vapors to clear the area.\nThe vapors will quickly rise in the air\ncolumn or rapidly dissipate.\nFor anyone outdoors. For anyone already indoors.\nThere are few people to evacuate. There are too many people to evacuate\nfor current available resources.\nThe threat seems stable but long-\nlasting.\nCircumstances are changing too quickly\nto evacuate safely.\nPage 285\n\nBACKGROUND ON TABLE 1 – INITIAL ISOLATION\nAND PROTECTIVE ACTION DISTANCES\nInitial isolation and protective action distances in this guidebook were determined for small\nand large spills occurring during day or night. The overall analysis, statistical in nature, was\nconducted using:\n•\nstate-of-the-art emission rate and dispersion models\n•\nstatistical release data from the U.S. Department of Transportation (DOT)\nHazardous Materials Information System (HMIS) database\n•\nmeteorological observations from more than 120 locations in the United States,\nCanada, and Mexico\n•\nthe most current toxicological exposure guidelines\nFor each chemical, thousands of hypothetical releases were modeled to account for the statistical\nvariance in both release amount and atmospheric conditions. Based on this statistical sample,\nthey selected the 90th percentile protective action distance for each chemical and category to\nappear in the table. A brief description of the analysis is provided below.\nA detailed report outlining the methodology and data used to generate the initial isolation and\nprotective action distances may be obtained from the U.S. DOT, Pipeline and Hazardous\nMaterials Safety Administration (PHMSA).\nDESCRIPTION OF THE ANALYSIS\nRelease amounts and emission rates into the atmosphere were statistically modeled\nbased on:\n•\ndata from the U.S. DOT HMIS database\n•\ncontainer types and sizes authorized for transport as specified in 49 CFR §172.101\nand Part 173\n•\nphysical properties of the individual materials\n•\natmospheric data from a historical database\nFor liquefied gases, which can flash to form both a vapor/aerosol mixture and an evaporating\npool, the emission model calculated one or both of:\n•\nthe release of vapor due to evaporation of pools on the ground\n•\ndirect release of vapors from the container\nThe emission model also calculated the emission of toxic vapor by-products generated from\nspilling water-reactive materials in water.\nSmall spills involve 208 liters (55 US gallons) or less.\nLarge spills involve greater quantities.\nPage 286\n\nDownwind dispersion of the vapor was estimated for each case modeled. Using a database\ncontaining hourly meteorological data from 120 American, Canadian, and Mexican cities,\nthe atmospheric parameters affecting the dispersion and the emission rate were selected.\nThe dispersion calculation accounted for both the:\n•\ntime-dependent emission rate from the source\n•\ndensity of the vapor plume (i.e., heavy gas effects)\nSince atmospheric mixing is less effective at dispersing vapor plumes during nighttime, day\nand night were separated in the analysis.\nIn the table:\n•\nday refers to time periods after sunrise and before sunset\n•\nnight includes all hours between sunset and sunrise\nToxicological short-term exposure guidelines for the materials were applied to determine\nthe downwind distance to which people may:\n•\nbecome incapacitated and unable to take protective action\n•\nincur serious health effects after a single, or rare, exposure\nWhen available, toxicological exposure guidelines were chosen from AEGL-2 or ERPG-2\nemergency response guidelines. AEGL-2 values were the first choice.\nFor materials without AEGL-2 or ERPG-2 values, emergency response guidelines were\nestimated based on lethal concentration limits derived from animal-based-studies. This\napproach was recommended by an independent panel of toxicological experts from industry\nand academia.\nPage 287","truncated":false,"body_characters":14149}