The severity of a chemical release depends on the toxicity, latency, transmissibility, and persistency of the chemical released. Toxicity measures the degree to which the chemical impairs human health. Latency is the time interval between exposure and the development of clinical symptoms. Transmissibility refers to the potential passage of the chemical between exposed persons and rescue workers, such as hospital staff. Persistency is the time it takes for the chemical to disperse. Where there is uncertainty about a chemicals persistency, responders will act with an abundance of caution. For example, the 2018 Novichok attack in Salisbury, England required a lengthy environmental remediation effort as the persistency of Novichok, which collects in low-lying areas, was unknown. The location of a chemical release and the proximity to residential and commercial areas is key to determining the extent of the likely exposure.

For chemical hazards, the National Fire Protection Association (NFPA) 704M rating system indicates the level of severity of exposure. This system uses numbers and primary colors on a label to define the basic hazards of a specific material. The system represents the risk posed by a particular substance, using a diamond with four colors: blue for health, red for flammability, yellow for reactivity, and white for special hazards. These categories are ranked on a scale from 0 (no hazard) to 4 (extreme hazard), as shown in this graphic.

Material Safety Data Sheets (MSDS) are also used to assess the severity of a chemical release. These documents, developed by the Occupational Safety and Health Administration (OSHA), contains information on the potential hazards associated with chemicals.

NFPA 704M Rating System for Chemical Hazards

The severity of a biological hazard depends on the type, location, and amount of the release, as well as the size, density, and characteristics of the population affected. For more information about Biological Hazards see the [link to Biological Profiles from DOHMH].

For radiological hazards, severity depends on a number of factors, including whether the dose was a partial body or whole body dose, the exposure rate, the duration of the exposure, the effectiveness of the radiation to harm human tissue, and if internalized, the organs affected. Exposure to a single, short-duration, high dose of radiation (a dose is the amount of energy absorbed by tissue per unit mass) can cause health effects such as acute radiation syndrome. Relatively low doses given over extended periods can cause a cumulative effect resulting in chronic health effects later. The unit of measurement for absorbed dose is the RAD (radiation absorbed dose).

Because certain types of radiation are more biologically effective than others, the absorbed dose must be multiplied by a quality factor to produce a dose equivalent that reflects the type of radiation to which an individual is exposed. The units of measurement for dose equivalent are the rem (roentgen equivalent man); its metric equivalent, the Sv (Sievert); and mSv (milliSievert). One Sv is equivalent to 100 rem and 1,000 mSv.

Doses received over a short period, such as a during a bomb blast, that are greater than 100 rem/1 Sv/1,000 mSv are likely to cause acute radiation syndrome. Acute exposure above these levels can lead to death absent medical intervention.

The table below describes symptoms of radiation exposure from different levels of dose equivalent.

Radiation Exposure and Associated Symptoms

Source: Nextbigfuture.com

Accidental chemical releases occur at fixed sites or when chemicals are in transit. Fixed sites include industrial facilities, open industrial areas, construction sites, commercial businesses, and even residential buildings with day-to-day materials, such as heating oil. Fires and explosions are possible secondary impacts of chemical releases, and they may also disperse the materials.

Chemicals are transported via highway, rail, air, maritime routes, and natural gas pipelines. A significant number of chemical spills and leaks happen during accidents when hazardous materials are in transit to and from storage or manufacturing facilities.

The locations at highest risk of accidental chemical releases include areas proximal to chemical plants; industrial facilities/storage sites; warehouses; and fuel stations. Throughout its history, New York City has had many industrial facilities located strategically along the waterfront to facilitate operations. Residential areas especially, low-income neighborhoods, may be near industrial facilities and present special concerns when recovery is considered.

Industrial and commercial businesses continue to operate on New York City’s waterfront in places such as Hunts Point in the Bronx; Newtown Creek in Queens and Brooklyn; the Brooklyn Navy Yard, Gowanus Canal, Sunset Park in Brooklyn; and Kill Van Kull in Staten Island. Flooding or coastal storm events heighten the risk of a hazardous materials (HAZMAT) release in these locations – the places in New York City at greatest risk from unintended chemical release.

The most likely targets for intentional chemical releases are densely populated, crowded places (such as tourist attractions, the subway system, and entertainment venues) and facilities critical to the life of the city (water supply reservoirs and distribution systems, power plants, ports, and hospitals). Financial centers and government offices are also potential targets for an intentional chemical release.

On a much smaller scale, common household chemicals (such as cleaning solutions) or materials (such as heating oil) are present in most buildings. An unintended release of these everyday chemicals in a home or in the workplace could pose a hazard to human health and life depending on the chemical and amount of direct exposure to humans.

Biological incidents can occur anywhere in the city. New York City’s high density neighborhoods provide biological agents the opportunity to quickly spread. These outbreaks could potentially start from, for example, restaurants or food markets selling tainted food, or from a combined sewer overflow outfall that exposes the public to raw sewage. The most vulnerable locations for intentional biological attacks are the same as those discussed for intentional chemical attacks.

Accidental radiological incidents are most likely to occur near facilities storing radioactive materials or waste. Buildings that store radioactive materials include hospitals, medical facilities, research and development facilities, colleges, and universities. Hospitals, medical facilities, research and development facilities, colleges, and universities may suffer small spills on occasion but these do not represent a threat to public safety.

The most likely targets for an intentional radiological attack are often cited as public spaces where contamination can be spread by outdoor conditions. Transit accidents or intentional vehicular attacks involving vehicles transporting medical isotopes also involve the outdoor environment.

Nuclear power facilities do not exist within New York City. The nearest nuclear power facility is the Indian Point Nuclear Power Plant in Buchanan, NY. A nuclear release from this plant (whether accidental or intentional) is not expected to expose New York City residents to harmful radiation unless an extremely large amount is released and combines with a very unique set of meteorological conditions.

When considering improvised nuclear devices, the target set becomes the city in general. According to the FEMA planning assumption, the damage zones for a 10 kiloton weapon extend out at least 3 miles from ground zero. The fallout plume could be at least 150 miles in extent (dose rate > 10 mR/hour).