EXPOSURE CONTROL AT HAZ-MAT INCIDENTS:
MICHAEL B. GUNN
Ph.D., REM, CSE/WSO
Like many fire service agencies in the United States, the City of Cincinnati (OH) Fire Division has been re-sponding to hazardous-materials incidents with a specialized unit (Squad 52) for a number of years. During that time, the protection of peripheral response personnel from exposures to toxic or hazardous products has relied on their distance from the hot (red) or the warm (yellow) zones (see Figure 1).
In the red zone, concentrations may exceed those immediately dangerous to life and health (IDLH). The yellow zone defines an area in which the quantities of toxic products in the atmosphere are below IDLH but greater than those permissible without special protection. They exceed threshold limit values (TLVs).1
The resulting area, excluding the red and yellow zones, is designated as the cold (green) zone. In this area, there are no exposures to harmful amounts of toxic materials. It is a safe, protected area. However, in reality, uncontrolled or unplanned events may allow the plume or vapor cloud to shift, causing an exposure to toxic products. We must prevent these liabilities from doing us harm.
In our experience, we have found it amazing how well placed the red and yellow warning and caution tapes are located at incidents by using criteria for isolating incidents such as those provided in the North American Emergency Response Guidebook. Our chemical field-testing has verified effective placement at most haz-mat incidents. But we know too well that “stuff happens.” When it does, we, as safety managers responsible for keeping 7,500 city employees from harm`s way, find it assuring to have a protection plan in place.
Sure, we have an arrangement for monitoring at these incidents. We even have from departments a team of “safety specialists” from varied backgrounds who have volunteered to respond and verify the identities of any contaminants and to monitor their concentrations in the atmosphere. These individuals can even identify major wind shifts and toxic cloud puffs. Yet, during routine events, we have received reports that suggested that we did not have our response arms completely around the toxic materials. Personnel stationed at the edge of the yellow zone have been characteristically uneasy about whether they were being subjected to hazardous exposures.
Ordinarily, there is little focus away from the red area, and communication with those assigned on the perimeter is scant. This nervousness appears to be relieved when a member of the monitoring team comes by with measurement data indicating that conditions are safe.
The in-between times are of greater concern, and they are more frequent at larger events. This lack of certainty and nervousness can translate into diminished confidence regarding the control of an incident and are more readily sensed by onlookers and the public than we realize.
Several years ago, we got the idea to try some chemically sensitive paper detection badges to see how they may work around a toxic material release. The idea arose from our success of distributing wetted pH strips to determine the presence of acidic atmospheric conditions subsequent to a release of oleum in our community. After several years of searching for and evaluating badges that would work well for outdoor detection, we adopted, two years ago, a badge that reacts to concentrations of potentially toxic gases and vapors in the air by showing a color reaction on the face of the badge. The chemicals are detected at levels comfortably below TLVs with a minimum of interference from other products. The wearer of the badge can independently determine the absence of toxic conditions by watching the badge. (Various types of exposure badges are used in controlled industrial workplace environments to monitor workplace chemical exposures and for emergency response operations in scenarios involving nuclear/radioactive material.)
The badges have some limitations:
They are not available for all potentially toxic materials.
They must be stored under controlled conditions. Since they are reactive by nature, they degrade when exposed to heat or certain substances. They must be stored under refrigerated conditions if they are to last for an extended period of time.
Some substances can interfere with an accurate response to the targeted toxic.
To obviate most of these limitations, we store them in refrigeration and open their packaging just before use. Competent technical staff monitor the atmosphere using multiple sensitive field instruments that identify interferences.
Using data gathered by the Hazardous Substances Emergency Events Surveillance, Annual Report, 1997,2 we evaluated badges for the substances most likely to be released during incidents in our jurisdiction. Those substances were ammonia, sulfur dioxide, chlorine, nitrogen dioxide, carbon monoxide, and mercury vapor. We field-tested the concept to determine what our responders thought about the product, the level of protection the badge provided, and the badge`s capacity to make responders comfortable.
In the spring of 1999, we were called to assist Squad 52 at a release of sulfur dioxide (SO2). We provided a specific toxic sensor instrument for monitoring inside the red and yellow zones and then distributed SO2 badges to unprotected responders serving as support for the haz-mat unit. Each individual was instructed to watch the badge face constantly for a discoloration, which would indicate that the material had been detected at amounts that would be protective if not exceeded. As luck would have it, SO2 is an excellent product for evaluating the badges because it has no detectable smell below TLV concentrations; therefore, some capability of detection is fundamental for personal protection. Responders were told that if the badge indicated that the substance were present, they would have to move farther from the chemical`s source, enter a sheltering location, or don additional personal protective equipment.
BADGE PROVES EFFECTIVE
This trial proved the badge to be effective. Responders unanimously found this method of detection acceptable. Fire, police, and other city response personnel not wearing protection and stationed away from the red and yellow zones really liked this detection method. The extra protection it affords employees translates into better protection for community members.
Responders have been trained to use the badges properly, including marking the date, time, and wearer`s name on them. The badge is attached near the collar (near the user`s breathing zone) with the front side exposed to the surrounding atmosphere. Once activated, badges will be sensitive for monitoring for 10 to 48 hours, depending on the chemical being monitored. As noted, wearers must frequently observe the badge for any indication that a toxin has been detected, in which case the badge will reveal the level of sensitivity (exposure dose).
In cases of detection, responders are instructed to retreat from the source of the toxic material or to shelter in place (by entering their vehicles, closing the doors and windows, and shutting off the ventilation system) and to notify command and the safety officer.
A member of the monitoring team then responds, conducts more tests of the atmosphere, and issues a fresh badge.
We plan to gather information from future events and further evaluate the badge`s performance. It is expected that it will be useful in the postincident medical assessment of personnel, improving the quality of reports on the extent of haz-mat situations and serving as additional evidence in cases involving releases that may have legal consequences.
This system would be especially indicated for detecting nerve agents and other chemicals of mass destruction. We have requested suppliers to extend the list of toxic materials for which this product may be used.
Special thanks to Charles Perry, district chief and hazardous materials coordinator in charge of the Environmental Crimes Unit for the Cincinnati (OH) Fire Department, and Duane Herth, district chief and risk manager of the Cincinnati (OH) Fire Department, for their help in preparing this article.
1. Threshold limit values, published by the American Conference of Governmental Industrial Hygienists, are the time-weighted concentrations for a given chemical substance for a conventional eight-hour workday and a 40-hour workweek to which it is believed workers may be exposed without adverse effects.
2. “Hazardous Substances Emergency Events Surveillance, 1997, Annual Report,” U.S. Department of Health and Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry, Atlanta, Georgia.
MICHAEL B. GUNN, Ph.D., REM, CSE/WSO, has been employee safety manager for the City of Cincinnati for 10 years. He served in the fire service for 23 years, 11 as chief of the Golf Manor (OH) Fire Department. He worked in the chemical industry for 29 years as a chemist and later as a safety director. He also served as a private-sector consultant on occupational health, safety, and environmental projects.