One Step Closer to a Safer America
These devices are critical in response to biological and chemical threats.
- By Richard R. Thomas, Lisa J. Rogers
- Sep 01, 2005
FIRE, smoke, explosion, medical trauma, and injury present obvious threats to health and safety. But when chemical or biological toxins are floating invisibly as "aerosols" in the air we breathe, the presence and nature of the hazard are much harder to determine and the consequences potentially far reaching.
The problem has drawn more attention recently because of the rise of terrorism. Though dangerous situations can arise from natural disasters or industrial accidents, the anthrax attacks of 2001 brought home the importance of rapid and effective detection and analysis of airborne pathogens, chemicals, and particulates. Chemical and biological attacks are now a very real possibility. First responders need tools that help them determine the presence, nature, and extent of a threat so they can stage an effective response.
That's where air samplers come in. Accurate air sampling is the crucial first step in the timely and successful detection and identification of a biological or chemical agent. Today, first responders such as police, fire, military, and medical crews have more choices in air samplers. They already deploy air samplers at large public events such as the presidential inauguration, the Super Bowl, the World Series; for indoor monitoring of government and corporate mailrooms and offices; and in searches for drugs or explosives.
The sample-detect-treat response to a threat takes the following sequence: The responder takes an air sample, then submits it for laboratory analysis to identify the organism, substance, or chemical. Laboratory analysis usually takes 24 hours, but some mobile labs yield results in one to two hours.
Speed is important. In the case of a biological threat, for example, first responders usually have a window of 24-48 hours between first exposure and manifestation of symptoms. Symptoms take that long to clinically manifest, allowing time between sampling and treating. Chemical attacks, however, affect their victims much faster. In either case, laboratories absolutely need to receive a meaningful air sample that accurately represents the situation. It must also be large enough for analysis. This requires proper equipment and proper procedure.
Choosing Air Samplers
The National Guard 1st Civil Support Team (CST), Wellesley, Mass., offers an example of a good procedure for a first responder team to follow when doing air sampling for laboratory analysis.
The National Guard CST, headed by science officer Capt. Andrew Parsons, monitors large outdoor events such as Boston's July 4 celebration (attended by 1 million people) and responds to individual incidents such as an infrequent "white powder" call at an indoor venue. The CST deploys the air samplers about 10 times per year, in addition to training on them. At each outdoor event, the CST sets up two wet concentrators and several passive chemical detectors in an array. The chemical detectors draw in air, analyze for threat agents, and send an alarm if they detect agents of a certain size. The detectors are essentially similar to smoke alarms: They collect no samples and are unable to detect an unknown substance. They only provide an alert to the suspected presence of specific hazards.
Parsons configures one of his air samplers with a particle mass counter used as a "trigger" that activates the sampler on detecting a certain count. At large outdoor events, team members often sit away from the sampler and are unable to activate it immediately when needed. Thus, the trigger.
In responding to an incident such as a white powder call, the team sets the wet concentrator to take continuous air samples while team members collect samples of the powder with a spatula or swab. Both samples are analyzed in the unit's mobile lab. The trailer-truck laboratory, equipped with sophisticated instrumentation such as immunoassay, PCR analysis, mass spectrometry, and polarized light and FTIR microscopy, can identify an unknown substance within one to two hours.
Other first responder units may not have ready access to mobile labs like the CST's, but the Guard unit's procedures for general surveillance and incident response provide sound models for the front-end air sampling.
First responders can choose from among several different types of air samplers. Current technologies for air sampling include dry filter, wet cyclone, and wet concentrator. They offer different pricing, features, and performance profiles.
When assessing air samplers, Parsons considered a bulky sieve impactor (Anderson type) sampler that functions with dry media plates that users must stock, maintain, and regularly replace. The Anderson type sampler also requires a separate pump to flow air onto the media plate--"more pieces, more maintenance," said Parsons, who selected the wet concentrator for its ability to collect meaningful samples. Its design allows the unit to draw 450 liters of air per minute to produce a large enough sample to yield substantive laboratory information and truly represent the space from which the sample is taken.
Samplers that draw lesser volumes of air--for example, as low as 75 liters per minute--yield inadequate samples for definitive lab analysis. These units are also unable to produce a highly concentrated sample and are more likely to damage or destroy spores in the collection process.
Parsons also rejected dry filter air samplers in which a small pump continuously collects microbes on a dry filter. Although collection is continuous in a 24/7 mode, "you can't grow the organisms later in the lab because they dry out and die," he said. They also get trapped in the filter, becoming difficult to recover for analysis.
Validation is Critical
Because an air sampler's effectiveness is key to identifying an agent, validation is critical. After the anthrax mailings in 2001, the U.S. Government Accountability Office (GAO) criticized the lack of validation in sampling and detection methods (mostly dry swabs on surfaces) used by government agencies in 248 U.S. postal facilities. GAO says the agencies collected samples from areas they judged likeliest to be contaminated, instead of "wide-area coverage" at mathematically determined distances. The GAO report concluded: "The sampling strategy . . . could not provide any statistical confidence with regard to the basic question: Is this building contaminated?"
For example, no anthrax was found in three rounds of tests in the West Trenton, N.J., postal facility, even though one worker had contracted cutaneous anthrax.
The inescapable conclusion is that mechanical collection methods produce misleading results. Samples taken with a cotton or foam swab or cue tip from surfaces of an affected area, for example, are likely to be unrepresentative of the area. You might be swabbing the sample from an unaffected rather than an affected area, or the chemicals or pathogens might remain only in the air rather than collect on surfaces. Aerosol sampling will give the best picture of the area.
To sum up: Air samplers represent a crucial tool in America's response to terrorism. Responders will be wise to choose effective air sampling methods that represent the entire space affected for credible laboratory analysis. As air samplers become more readily available and more sophisticated, first responders will get the edge they need to stay on top of aerosol emergencies. Effective air sampling helps the nation step closer to being safer.
This article appeared in the September 2005 issue of Occupational Health & Safety.
This article originally appeared in the September 2005 issue of Occupational Health & Safety.