A freight train derails, spewing a cloud of toxic gas… A white powder leaks from a package in the local post office… A leak at a chemical plant results in toxic vapors inundating a residential area… A fire breaks out at a bulk petroleum fuel depot…
These are just a few examples of actual incidents that have occurred in recent years — and are the types of incidents hazmat/first responders need to be prepared for. This is notwithstanding the fact that the number one hazmat response is to fuel leaks and spills, mostly from transportation incidents.
Detect, identify and quantify
Hazmat teams must be able todetectand thenidentifyandquantifyany suspect toxic material as fast as possible. As such, they arrive at the scene equipped with a wide range of detection and identification devices.Most responders are familiar with electrochemical sensors that detect gases like carbon monoxide and chlorine, and with photoionization detectors (PIDs) that detect the VOCs we now call toxic industrial compounds, or TICs. Let’s call these devices “detectors” for want of a better word. They detect and can quantify but do not identify. PIDs have become the “broad spectrum” screening tool of choice.
Some are familiar with portable gc/ms and IR. These and other related techniques, like Ion Mobility Spectrometry (IMS), can detect, quantify and identify many of the target compounds of interest, although with an increase in bulk and price.
Here’s the catch. Some existing technologies work fine for solids and liquids, some for vapors and gases. None seem to work well for both.
Also, as detection capability approaches the ppt level, cost and complexity go up, while ease of use, portability and response times suffer. Ditto for identification capability. And training is a whole other issue!
Appropriate devices
The SEL/AEL(1) list of authorized equipment helps guide the selection of appropriate devices. Detector tubes and test kits provide low-cost snapshots of the presence and approximate concentration of a number of toxic compounds. Electrochemical sensors detect single gases such as chlorine and carbon monoxide.A new generation of the workhorse PID, now available with ppb sensitivity in both PID and PID/4gas configurations, provides rapid detection and screening for most VOCs, TICs and WMDs in less than one second. IMS-based chemical detectors identify and quantify a number of chemical agents, as do SAWS-based devices.
Support from GC/MS provides detection, identification and quantification for many gases and vapors. IR provides identification of powders and non-volatile liquids.
These complementary devices offer rapid detection, followed by identification and quantification for most of the toxics of interest.
Today’s tool box is filled with individual units that are often faster, more sensitive, easier to use and less expensive than those developed just a few years ago.
PIDs and PID/4gas still represent the best, broadest range method of confirming the presence of most hazardous atmospheres. PIDs and PID/4gas units are now available with ppb detection capability, full TICs and WMD software packages and wireless communications.
A new development, patented “Fence Electrode” technology, results in optimal performance even in the extreme humidity often found at fire scenes and especially during decontamination.
Lower and lower
Why ppb? In today’s environment, you have to be prepared to detect VOCs, TICs and WMDs at lower and lower levels. It only makes sense to utilize the extra sensitivity and resolution of a ppb PID, especially one that performs when the humidity is extreme.Just like PIDs, four-gas units have been around for a while. Designed primarily for confined space entry, four-gas units typically handle LEL, O2, H2S and CO, although sometimes other toxics can replace one or more of the standard sensors.
There are two fundamental design philosophies for PID/4gas units. Traditionally, the unit has primarily been designed for confined space entry with the added protection of a PID for detection of VOCs. These units are often designed to be worn first and carried second; in other words, they are primarily a piece of personal protective equipment and second, a screening tool. This philosophy has been carried to its logical conclusion by the introduction of new low-cost units, making such devices affordable for just about every confined space entry situation.
There is a second approach. Since most PID/4gas units have limited PID range, in reality often from about 1 ppm to 2,000 ppm, many hazmat teams see a need for a PID with ppb capability, as well as a PID with range up to 10,000 ppm. This ensures there are no gaps in detection capability all the way from ppb to LEL. In the past this meant a technician would need to carry a ppb PID, a 10,000 ppm PID and a PID/4gas in order to provide equivalent full coverage.
Combining best features
Fortunately, a unit is now available that combines the best features of the full-range PID, i.e. ppb to 10,000 ppm, with a four-gas unit all integrated into one lightweight package. These units are not designed to be primarily a piece of confined space entry equipment; rather they are intended primarily as a screening tool with confined space entry capability. As a result, these units offer the fastest response to VOCs, TICs and WMDs, utilizing a flow path that minimizes sample loss and degradation for optimal response to those difficult-to-detect agents.The recent huge fire at an oil depot explosion just outside London, England provides a good example of the use of PID in first response. The Bedford and Luton Fire and Rescue Service in the U.K. were called upon to assist at the Buncefield oil depot explosion, which made international headlines as the biggest-ever peacetime explosion in Europe. The responders, who described the scene as total devastation, used ppb PID instruments to determine which areas of the site were potential explosion risk areas. Generally, readings were found to be in the 50 ppm range, but some areas exceeded 500 ppm. Those areas were found to have large quantities of hydrocarbon product among the rubble, and the responders were able to cordon off all the dangerous areas and avoid more explosions and fires.
In summary, new developments have dramatically enhanced capability at hazmat incidents. The ubiquitous PID, long the tool for broad spectrum screening, has been enhanced by the incorporation of Fence Electrode technology, which enables first responders to utilize a PID or a PID/4gas that offers ppb to 10,000 ppm range in situations where previously high humidity and moisture would not allow its use. PID/4gas units can now be configured primarily as survey tools, reducing the need to carry multiple units on scene.
