|At any point and time in which hazardous materials air monitoring is discussed, the conversation usually is peppered with words such as “Wheatstone bridge,” “relative response correction factor” and other similar pieces of the hazmat lexicon that apply to the technician level arena. What is often forgotten in the present day is that air monitoring is not only being performed at the technician level, it is also being performed by operations level personnel as members of fire departments that do not have a hazmat team. Such personnel need to know more than just how to turn a meter on and look at readings, as air monitoring activities just described can indeed be a life or death situation.|
Air Monitoring Today
In this discussion, we will first look at what has changed in the air monitoring world at fire departments without technician level responders. In years past such fire departments left air monitoring to those organizations with technician level capabilities. As the price of air monitoring equipment decreased to a more affordable level and the ease of use of such equipment increased, the acquisition and use of basic four gas, and other meters became more attainable by those departments not in the technician level arena. Paralleling this trend was the need for quantitative air monitoring at scenes involving natural gas leaks or carbon monoxide alarm activations. The trend was then exacerbated by our increased knowledge of the hazards of first carbon monoxide and then hydrogen cyanide at structure fire scenes, especially during the conduction of overhaul activities. The National Fire Protection Association (NFPA) also underscored the need for air monitoring training for operations level hazmat responders in the 2008 revision of the NFPA 472 Standard for Competence of Responders to Hazardous Materials/Weapons of Mass Destruction Incidents, in which the mission-specific competency for air monitoring and sampling was first developed and published. To use the state of North Carolina as an example, operations level personnel that wish to become certified in the air monitoring and sampling mission-specific competency complete a 16-hour course of training in order to learn and demonstrate competency in the performance of air monitoring activities.
Air Monitoring Competency
In order to competently perform air monitoring activities, operations level personnel should first begin with a thorough understanding of basic air monitoring concepts and how the equipment utilized operates. For example, air monitoring equipment is not something that can just be thrown in an apparatus compartment and forgotten about until it is needed at an incident scene. Such equipment should first be stored in a manner that will protect it from jarring impacts and changing environmental conditions. Each sensor should be calibrated as specified by the manufacturer, normally at a monthly interval. Calibration involves flowing a known concentration of gas through each sensor. The meter then corrects the sensor readings to the gas concentrations that have been previously programmed into the meter. Ideally each sensor should also be “bump tested” prior to each use by flowing calibration gas through the sensor and then ensuring the meter readings match the values displayed on the calibration gas cylinder. Challenges often arise in bump testing sensors in the field, as the purchase of the calibration gas or gases needed is expensive and it is often impractical to carry such cylinders on apparatus. If bump testing is not possible prior to the use of a meter, personnel should at least perform a “fresh air check” in which the sensors are reset in a clean air environment to reflect the proper readings.
The meters utilized in the performance of routine air monitoring activities vary from very simple to complex. Single sensor meters can be used, in which the name says it all — the meter contains a single sensor to indicate the concentration of a specific gas or vapor; or the flammability of an environment. Four gas meters are often employed at incident scenes, as they can be used to monitor several parameters at once. The “standard” four gas meter setup contains sensors measuring the concentration of oxygen, carbon monoxide, hydrogen sulfide, and the flammability of the environment — measured in percent of the lower explosive (also known as lower flammable) limit. Some agencies utilize four gas meters with the hydrogen sulfide sensor replaced with a hydrogen cyanide sensor for structure fire overhaul operations.
When to Use a Meter
Let us now turn to a discussion of the types of incidents in which operations level hazmat responders may utilize air monitoring equipment. We must again underscore that such personnel should receive thorough training in air monitoring equipment and techniques prior to performing the aforementioned functions. Natural gas leaks are a common occurrence in present times due to the widespread use of natural gas as a fuel source and the frequent occurrence of ruptured underground lines due to construction activities increasing as our economy improves. Natural gas has a vapor density of less than one, which means that it rises in the air column. Its main constituent is methane, and we are most concerned about the flammability of the environment proximate to any leak. We rely on our combustible gas indicator sensor to discern the flammability of such an environment in terms of the percentage of the lower explosive limit (LEL) of the product. In simple terms, how close are we getting to the lower explosive limit? Our level of concern for areas that are not considered to be a confined space is 25 percent of the LEL. We also need to remember the concept of relative response, in that if we are monitoring for any gas or vapor other than what the sensor is calibrated to, we need to multiply the meter units displayed on the sensor readout by the relative response correction factor for the gas or vapor being monitored — which is given by the manufacturer — to determine the percentage of the LEL. We are fortunate in my department that the combustible gas indicator sensors we use are calibrated to methane — again the largest constituent of natural gas; therefore the relative response correction factor is negligible. Departments in areas without natural gas service should familiarize themselves with liquefied petroleum (LP) gas, as it is often used as a fuel in such areas and is present in cylinders or tanks. LP gas is unlike natural gas in that it has a vapor density of greater than one and will descend in the air column.
Another type of response in which operations level hazmat responders may find themselves performing air monitoring activities is that of carbon monoxide calls, which can be initiated by alarm activations or the presence of exposure symptoms in residents — e.g. flu-like symptoms and cherry-red skin. Carbon monoxide is odorless, colorless, flammable, and is produced by incomplete combustion — such as a malfunctioning heater flame. The vapor density of carbon monoxide is reported as 0.97, which means that it should slightly rise in the atmosphere. The word “should” is used due to the fact that since the vapor density is so close to one, carbon monoxide can actually become neutrally buoyant (float) or even sinks in the air column depending upon temperature and humidity levels. This characteristic underscores the need to monitor both high and low in the air column; and to use the proper techniques of monitoring slowly and methodically. Responders should also wear structural fire fighting gear with SCBA when monitoring. Carbon monoxide sensors are direct reading instruments that display the concentration in parts per million (ppm). The level of concern for persons in indoor areas is nine ppm. We may also monitor for carbon monoxide concentration at structure fire scenes to determine when it is safe to doff respiratory protection. In times past, many departments utilized the NIOSH Recommended Exposure limit of 35 ppm as the threshold below which respiratory protection could be doffed by firefighters. Many departments now follow the same EPA guideline used for civilians in indoor areas of nine ppm to ensure the safety of personnel.
Detecting Hydrogen Cyanide
The final type of response we will discuss in which operations level hazmat responders may perform air monitoring activities is the detection of hydrogen cyanide concentrations in post-structure fire conditions. Hydrogen cyanide is produced by the combustion of synthetic materials, which are heavily prevalent in modern day structure fires. Hydrogen cyanide produces the same type of symptoms as carbon monoxide in humans; however the treatment for exposure is much different. High flow oxygen and possible hyperbaric chamber application is used to treat carbon monoxide exposure, while an antidote such as amyl nitrite is used to treat hydrogen cyanide exposure. Since it takes less concentration of hydrogen cyanide to result in detrimental physical effects than with carbon monoxide, the level of concern is lower at the NIOSH Recommended Exposure Limit of 4.7 ppm. Hydrogen cyanide sensors can also be used to monitor structural fire fighting turnout gear to evaluate any residual hydrogen cyanide that may off gas and to determine if the field decontamination of gear — whether by off gassing or washing — is effective.
In summation, many fire departments now utilize air monitoring equipment at the scenes of natural/LP gas leaks, carbon monoxide exposures and structure fires. What was once only within the realm of hazmat teams and technician level personnel is now the reality for most operations level personnel. Such personnel should receive appropriate training in the use of air monitoring equipment; and in the operation and care of same to ensure the safety of civilians and emergency response personnel alike.
As always, stay safe out there and be sure to visit the North Carolina Association of Hazardous Materials Responders website at www.nchazmat.com.