Introduction

Hazardous materials can be classified as chemical, radiological, or biological agents that can cause human illness when contacted. The basic physical and chemical properties of a hazardous material determine the manner in which victims/patients are exposed, the degree of morbidity and mortality associated with a given “hazmat” event, the type of decontamination necessary, and the type of personal protective equipment (PPE) required in the response.

Each hazardous material has a unique set of chemical properties. Here we will discuss the chemical properties of a hazardous material that can be used to place it into a group allowing assessment of the potential for contamination, the extent of exposure, the decontamination process, and type of PPE required.

One of the best examples of how the chemical properties of a substance can affect a hazmat response can be seen in the “sarin gas” attacks which occurred in Japan. On June 27, 1994 in Matsumoto, a Japanese terrorist released sarin gas, producing symptoms consistent with a cholinergic syndrome in approximately 600 individuals over a few hours. Over that time period, eight of the 53 prehospital responders developed symptoms of sarin exposure [1] and one of those responders required hospitalization for treatment [2]. Similarly, 11 of the 18 physicians caring for these patients in one emergency department developed symptoms, six of whom required treatment after exposure to contaminated patients alone [3].

In Tokyo, Japan, on March 20, 1995, a terrorist released sarin into five subway cars on three separate rail lines. As a result, 11 commuters were killed and over 5,000 patients required emergency medical evaluation. Again, victims quickly developed symptoms of cholinergic agent exposure and 640 victims arrived at the closest hospital (St Luke’s International Hospital) over just a few hours. Although unable to fully decontaminate all who arrived, simple measures taken (removal of clothing, optimization of ventilation in patient waiting areas, and frequent rotation of staff through waiting areas) resulted in limited exposure of medical staff. No staff required treatment for toxic exposures [4]. Of note, several other hospitals reported staff members who required treatment for exposure to sarin (25 of 39 prehospital providers required treatment at one facility) [5].

Types of contamination

In order to understand the effect of chemical properties on hazardous materials response, we must first differentiate between exposure and contamination and discuss the types of contamination that can occur.

When an object or individual is exposed to or comes into contact with a hazardous material, that object or individual may or may not become contaminated with the substance. Contamination occurs when the hazardous substance is physically transferred from the source to an object or individual.

Primary contamination occurs when an object or individual comes into direct contact with a hazardous material in such a manner that the material is transferred from the source and is physically on the object or individual. This type of contamination is most common in victims at the hazmat site, as well as first responders including police, fire, and EMS personnel [6].

Secondary contamination occurs when an object or individual comes into contact with a contaminated object. The hazardous material on the object may then be transferred to the clean object or individual, resulting in secondary contamination. Secondary contamination is the most common manner in which health care workers, such as emergency department staff receiving patients from the field, become contaminated after the release of a hazardous material [6,7].

Contamination may be best understood through the example of a child with dirty hands. A child gets out of the bath and is clean (non-contaminated). The child goes out to play in the yard, finding a mud puddle (the contaminant). After playing in the mud, the child has mud all over his hands (primary contamination). The child then goes inside and pets the dog, leaving dirty handprints on the dog (secondary contamination). The child washes his hands (decontamination) and no longer has any evidence of playing in the dirt. The child’s father later arrives home and gives his perfect child a hug. He pets the dog and notes dirt on his hands (secondary contamination). The father looks at his dog and asks, “Have you been rolling in the mud again?”

Both primary and secondary contamination may occur in an overt or covert manner.

Overt exposure occurs when something is obviously contaminated or exposure is known. Overt exposures may become obvious when a material causes rapid onset of symptoms, or the material is a large liquid or solid that can easily be identified. Both of the examples above (the release of sarin and the child with muddy hands) illustrate overt exposures. The release of sarin “gas” (actually a liquid vapor) may be too small to detect visually but the rapid onset of symptoms allows for early identification of contamination. The dirt on the child’s hands illustrates a material that can be visually identified despite the distance in both time and space from the scene.

Covert exposure occurs when an object or individual does not have obvious contamination or does not immediately know that he or she has been contaminated. Covert exposure may occur when the hazardous material is associated with delayed onset of symptoms or a hazardous material is too small to see. Biological agents are commonly associated with covert exposure. As illustrated in the example below, biological agents not only are too small to see but also have an incubation period in which exposed individuals are not aware that they have been exposed.

In the fall of 2001, envelopes filled with spores of Bacillus anthracis were mailed via the United States postal services to multiple locations. Individuals inhaled these microscopic spores when they were released from the envelopes during the mail sorting processing, delivery of the envelopes, or opening of the envelopes. Initially, ten patients became ill with symptoms of inhalational anthrax and four died. None of these individuals were aware that they had been exposed [8]. As awareness of the anthrax attacks spread, early recognition, aggressive medical management, and prophylactic treatment resulted in only six deaths in the 22 individuals known to have become ill [9].

An understanding of the types of contamination allows first responders to be aware of the potential for contamination and protect themselves and others. Only with vigilance can we control or mitigate secondary contamination. Mitigation is critical and can prevent a small incident from becoming a mass causality incident or true disaster.