Tips for Understanding & Using Your Gas-Detection Equipment: Hazardous Material Cbrn

Tips for Understanding & Using Your Gas-Detection Equipment

Much like golf, air monitoring can be considered both an art and a science. Each requires three distinct components: 1) good technique, 2) the appropriate equipment and 3) the knowledge and experience to use and apply the tools and techniques appropriately. Unfortunately, as firefighters and hazmat technicians, we spend far too little time honing our skills and ensuring that we can competently use our air-monitoring and radiation-detection equipment to make sound decisions.

Why We Monitor
We all know that air monitoring and radiation detection are performed to detect dangerous atmospheres. Some examples: Firefighters inspect occupancies potentially charged with colorless and odorless carbon monoxide (CO) gas generated from faulty appliances; firefighters and EMS personnel investigate chemical suicides in which hydrogen sulfide, hydrogen cyanide or phosphine gas were generated in an enclosed area; hazmat teams check leaking cylinders or other gas and vapor releases; and technical rescue personnel monitor confined spaces for toxic gases, oxygen deficiency and flammable atmospheres. Clearly, there are many reasons we may be called upon to use our air-monitoring equipment, so we must have a solid grasp of how to best approach these incidents.

Good Technique
Good technique is essential for consistently and accurately detecting atmospheric hazards. But to have good technique, we must really understand the science of gas detection as well as the limitations of our equipment. For example, some gases (e.g., ammonia, hydrogen, methane and acetylene) tend to rise since they are lighter than air, while other gases (e.g., chlorine and propane) are heavier than air and tend to sink. It is therefore important to monitor at the appropriate location when trying to find a known gas, and monitor both high and low at the location when searching for an unknown gas.  

Further, sensors take time to respond. Some sensors are comparatively fast, like photoionization detectors (PIDs), which respond in a few seconds. Other detectors are somewhat slower, such as electrochemical sensors, which take 20–40 seconds to respond. This means that if it takes you 30 seconds to walk across a 200' warehouse, your electrochemical sensor is still analyzing the atmosphere at the door, and you may have traversed a life-threatening atmosphere in the meantime. It is therefore crucial to know the response time of your detection equipment. This information can be found in the instruction manual listed as t90—the time it takes for the sensor to reach 90% of the full response. Special responses, such as confined space incidents, may require even longer sampling times due to the additional travel time of any attached hoses. A good rule of thumb is to add 1–2 seconds per foot of hose.

New Technology & Old Methods
Air monitoring technology has been advancing at an extremely rapid pace over the last 10 years. Presently, firefighters have the ability to detect almost every chemical down to the part-per-billion level. The technology—in the form of new, easy-to-operate and maintain gas chromatography mass spectrometry instruments (such as the GUARDION by Smiths Detection)—exists to separate complex mixtures and to readily determine both airborne and aqueous (dissolved in water) contaminants at parts-per-billion levels within a few minutes.

Although technology has advanced greatly, often the simplest of tools are the easiest and most cost-effective to use. One example of this is pH paper. Also known as litmus paper, pH paper is an effective tool for corrosive atmosphere monitoring. It’s best used when it is half wet and half dry. The wet portion of the pH paper indicates highly soluble corrosive materials (e.g., ammonia) faster and at lower airborne concentrations, while the dry portion indicates less soluble corrosive materials (e.g., hydrogen chloride) more readily. Surprisingly, pH paper is highly sensitive and is able to detect corrosive gases and vapors down to the parts-per-million range.

Using Your Equipment
Air monitoring should be performed systematically when approaching the suspected area of release (in the hot zone). So how can we optimally use all of this detection and monitoring technology? You need to know which equipment to use and when. In other words, what equipment should we take into the hot zone and in what order should we consider the results? There is a defined order of detection and air monitoring that directly protects the entry team, and indirectly protects the entry team by ensuring that the monitors are not damaged.

Generally, detection and air monitoring should be performed in the following order:

  1. Gamma radiation from a distance (from the suspected cold zone)
  2. Corrosive gases and vapors (as the entry team approaches the hot zone)
  3. Oxygen levels
  4. Flammable gases and vapors
  5. Toxic gases and vapors (as well as alpha, beta and gamma radiation)

We typically monitor for most of these hazards simultaneously. Multi-gas meters now have the ability to simultaneously measure gamma radiation, oxygen levels, combustible gases and selected toxic gases, such as carbon monoxide, hydrogen sulfide and/or hydrogen cyanide. The only task left is to tape a piece of half-wet/half-dry pH paper to the multi-gas meter to complete the system.

Follow the Readings
Disastrous results can occur when air monitoring is not done properly. In the past, hazmat teams have neglected to use pH paper with their multi-gas detectors and have unwittingly destroyed them by placing them in a corrosive atmosphere. Another common mistake is to move too quickly when performing air monitoring activities and enter a flammable atmosphere before the combustible gas indicator (CGI) has had a chance to even register a reading. There have also been instances where people have monitored confined spaces and have received normal background readings dozens of times, then their meter alarms one time and they assume the meter is broken, and they disregard the results to their peril. Always assume the meter is giving you the correct results when it alarms and take the appropriate actions! Air monitoring is one of the bread-and-butter skills any firefighter and hazmat technician must perform well.