Step #2 - It is crucial to sample environments that can ignite or combust simultaneously with the oxygen levels. Since combustible gas indicators (CGI) need sufficient oxygen to oxidize a sample, adequate oxygen levels have to exist in the sampled environment. CGI's also sample environments on a percent basis, and, since 1 percent equals 10,000 parts per million (ppm), a material will not combust until there is a large amount present. So, this step is measuring not only flammability and oxygen content, but also large amounts of an airborne material. Absence of a reading on a CGI does not necessarily indicate the environment is hazard free. A toxic hazard that the CGI could not detect may exist. We also use a radiation detector on Step #2 as a precaution to rule out the presence of radiation early in a response.
Step #3 - Many monitoring instruments today are manufactured with sensors that detect flammability, oxygen, and the toxic gases hydrogen sulfide and carbon monoxide all in the same instrument. These combination instruments are required by the OSHA permit-required confined-space regulation (29 CFR 1910.146). For many instruments, Step 3 can be achieved at the same time as Step 2. Other instruments can be utilized individually to check for specific toxic gases, but sampling should always be conducted along with a CGI and oxygen sensor for safety.
Step #4 - Colorimetric tubes can be used if the environment is known and the needed tube is available. Each tube can be read to determine the amount of the gas in the environment. Similarly, new chip system detectors can also be used as colorimetrics. If the environment is unknown, several manufacturers offer a tube system by which several tubes can be used at the same time to categorize an environment. A positive result may indicate the classification of the gas/vapor in the environment.
Step #5 - A PID (photoionization detector) can be utilized to quantify an environment after the material is identified. PID's can also verify concentrations found with colorimetric tubes or can be relied upon solely to find environmental concentrations. PID's should always be accompanied by CGI's and oxygen sensors for safety and because PID's commonly do not measure more than 1 percent or 10,000 ppm. It is important to remember that PID's measure small concentrations of an airborne hazard that are in the toxic range rather than the flammable range.
Step #6 - Depending on circumstances, sampling efforts may utilize both radiation detectors and/or weapons of mass destruction (WMD) agent detectors early in the procedure. A precaution with these detectors is that they may not be intrinsically safe, so they should not be used until Step #2. If they are accompanied by a CGI with an oxygen sensor, and a flammable environment can be ruled out, these detectors may prove to be invaluable. As a result of the terrorism and "dirty bomb" threat, many hazmat response teams are currently screening every incident for radiation.
Step #7 - Use other expensive and intricate instruments as needed. This step may include the use of infrared devices although some teams have adopted guidelines that bring the sample to the instrument instead of taking a bulky and intricate operating device into the hot zone. This type of thinking also works well with the wet chemistry type of identification kits that also utilize open flames in their processes. Finally, some teams also use vacuum canisters that can capture a gas or vapor in the release area and then be analyzed at a later time at a laboratory.
These steps should be utilized on the initial entry to categorize an atmosphere to protect not only personnel but the instruments themselves. Subsequential entries may find only selected instruments being used depending on initial findings or further environmental quantifying or qualifying. Paramount findings on the first entry would rule out excessively dangerous pH levels, flammable environments, and the presence of radiation. Entry personnel can then focus on the toxic hazard by identifying the hazard and its airborne concentration.
We have used a small plastic bucket with a metal handle to sample environments with this procedure. All of the initial entry environmental samplers fit nicely into the bucket. Upon entry in the hot zone or release area, one entry person would conduct the sampling with each step's equipment while the other entry person holds back with the sampling bucket while still maintaining close contact. The bucket person radios sampling results to team officials in the cold zone.