Air Monitoring

(This is part two of a two part series.)

This article is designed for regular firefighters. And as we will see, you really are involved in hazardous materials response from a certain point of view, even if you don’t realize it.


Part two of this article recognizes various monitors and detectors and what you need to know about them to perform your job safely.

Photoionization Detectors

A PID uses an ultra violet light source to break down chemicals into positive and negative ions that can easily be measured with a detector. PIDs can detect organic and some inorganic gases including ammonia, arsine, phosphine, hydrogen sulfide, bromine and iodine. Because of their sensitive nature, they can detect small amounts of hydrocarbons in the soil. Sick building calls are on the increase and the PID is a valuable tool in identifying possible hot spots within the building. The PID is a valuable resource in protecting responders and the public from toxic materials. The best way to really learn how to use a PID and to be able to interpret any readings is to use the PID all of the time.

The most common material that a PID reacts very well to is solvents, all flammable liquids. The quicker and higher the rise, the more flammable the material is. The PID is used to determine the presence of toxic risks, but many toxic risks also present a fire risk as well.

Ionization is affected because the UV lamp cannot ionize the contaminant as well through moisture or dust. This is similar to driving your car through fog or mud as both obscure the headlights. Correction factors can’t be used if chemical is unknown. In order to properly analyze the meter’s result, you must know the ionization potential of both the lamp installed in the meter and the material being analyzed.

Colorimetric Tubes

Tubes provide a fast response, are low technology and low cost and offer an excellent tool for first responders. However, tubes can be inaccurate up to 25 percent of the time, sometimes even higher. There is no automatic alarm like those on meters. Each tube must be analyzed by the operator. Unless the tube is connected to an automatic pump, the tube must be used with a manual pump that must be pumped up to 50 times. The tubes have a shelf life that must be adhered to. A tube is a one shot attempt at monitoring. If you have a house with 10 rooms, you will have to use 10 tubes — one for each room — to accurately monitor the entire structure.             

Single Gas Monitors

Single gas meters are easy to read, easy to use, small, inexpensive — a few hundred dollars or less) and can easily be clipped to turnout gear or SCBA. They only detect one gas however and must be used in concert with other meters in order to get a true picture of the atmosphere in a room. Just because your single gas meter doesn’t detect anything does NOT mean that there is nothing hazardous in the room!

Four Gas Monitors

Four gas meters are the most versatile. They can come pre-equipped for confined space rescue (O2, CO, H2S and LEL) or they can be customized to meet your department’s individual requirements. They can also be grouped with a PID for maximum effectiveness. They will not detect radiation and can run over a thousand dollars.

SpilFyter Strips

One of the easiest of multiple chemical tests for street responders is the chemical test strip. Much like pH paper, these strips are for testing unidentified liquid samples and can assist in identifying unknown materials. There are five tests on each strip and the manufacturer intends that the strip be dipped into the unidentified material. However, it is recommended that a sample be taken from the identified material using a pipette and placing a small drop onto each test area. The oxidizer risk test is important as it is a quick test for potentially explosive materials. The test for fluoride assists in the identification of hydrofluoric acid (HF).

What You Need to Know About Your Monitor

The response time of a meter is the amount of time that the meter takes to report a reading that is 80 to 90 percent accurate. The reaction time varies with the type of sensor and whether you are sampling with a pump. Instrument response varies with different chemicals. The response time can range from one second to one minute.

The recovery time of a meter is the amount of time that it takes the meter to clear itself of the air sample. This time is affected by the chemical and physical properties of the sample, the length of sampling hose and the amount absorbed by the meter.

The correction factor is the way the monitor reacts to a gas other than the one it was calibrated for. To better understand correction factors, let’s consider an analogy to time zones. A clock set to Eastern Standard Time here in Maryland is accurate only in that time zone. To use that same clock in California (Pacific Standard Time) it is necessary to adjust that time by subtracting three hours from the time displayed — applying a correction factor.

Materials such as halogenated hydrocarbons and high concentrations of flammable gases can affect sensor reliability and poison the sensor causing damage that is sometime irreversible.


One of the best methods for learning how to effectively use air monitors is to use them for every incident, even when the preponderance of information tells you that you really do not need all of the instruments or that instruments may not be required at all. It is a good habit to carry monitors on calls that do not involve hazardous materials so you can learn what they do or do not react to. The monitors can be used when you do company tours or inspections so you learn what you may expect to find in facilities under normal conditions.

A common mistake is for a firefighter to check the air only in the actual work location — room of origin — of floor but not check in other areas of the structure. It is an especially good idea to monitor at the pump panel to make sure that your engineer is not being exposed to high levels of CO.

A meter should be placed on at least one entry person, particularly in confined spaces where ventilation may be more difficult. Monitoring should be started before anyone enters the Hot Zone, during the entire length of the incident and include one final reading prior to the termination of the incident. All meter readings should be recorded along with their time for purposes of incident documentation. This may prove especially valuable should the incident be subject to court proceedings at a later date. One person should be posted at the entry point with a meter to monitor continuously and record the readings. This person can be from the HazMat team but this is not a requirement. When utilizing a hose and pump to pull a sample from a certain depth, allow one second per foot of hose for the sample to reach the meter. The OSHA Confined Space Standard, OSHA 1910.146 requires that O2, CO, LEL and H2S be continuously monitored for.

Sick Buildings

The source of a sick building is usually the building itself or the contents. Potential causes include the HVAC system, new furniture or carpet, occupants bringing chemicals such as pepper spray or mace, industrial processes or poor employee relations with management. People desiring to leave early for the day or weekend may also be a cause in addition to a recent case or cases of other sick buildings being in the news.

Any substance from outside the structure will be brought in through the fresh air intakes, which may also lead to a chemical build up on the filters. Building personnel may place HTH tablets in the drip pans of the chillers to reduce bacteria, producing large amounts of chlorine in the process. New carpets, wall coverings or furniture may off gas for up to one year. Storage areas often contain chemicals which may be the source of the odor or incident. Recently cleaned areas may have chemical residues left behind by the cleaning chemicals or processes. Start with the area that has the most affected people as that area probably has the highest concentration causing the problem.

Freon may be a responsible culprit in summer due to an increased use of air conditioning. CO may be a responsible culprit in winter due to the increased use of heating and CO being a product of incomplete combustion.

If nothing is found during your investigation, say that your meters could not detect anything. Saying that “the building is clear” or “there is nothing there” could open you and your department up to liability if a problem is found later. You may not have the proper meter to detect what is in the building or the amount present may be too small for your meter to detect. Another possibility may be that the building was ventilated prior to your arrival. In any event, if you cannot find anything but the little voice in the back of your head tells you that something is wrong, it would be a good idea to get a HazMat team en route as they have more sensitive detection gear.

General Operating Guidelines

It is imperative that your department has a written procedure — whatever your department calls them is fine — when it come to air monitoring. A written procedure ensures that the same things are done in the same way every time by everyone. It prevents A Shift doing it one way, B shift doing it another and C Shift doing nothing. A written procedure should spell out such things as when monitoring will take place, who will be responsible for not only monitoring, but care and maintenance as well. This procedure will address training issues as well and could make the difference between winning and losing should a lawsuit be filed against the department.

Calibration Methods

In a Bump Test, the meter is exposed to a gas in order to ensure that the sensor responds. For every day that a meter is not bump tested, there is a 1/250 chance that the meter will not be able to respond to gas. During Field Verification, the detector is exposed to a given gas and the operator ensures that the meter’s display is within +/- 10 percent of the concentration value of the calibrations gas in the cylinder. Field Calibration can be performed either in the station or in the field during an incident. Field Calibration takes Field Verification a step farther if the value found during verification is greater than +/- 10 percent of the concentration value and adjusts the sensor according. In most meters, this adjustment is done automatically. Factory Calibration requires that the unit be returned to the manufacturer for calibration and is the least desirable due to additional costs and lost use of the meter. Calibration verifies that the sensors remain accurate. If exposure to the test gas indicates a loss of sensitivity, the instrument needs adjustment. If the sensors cannot be properly adjusted, they must be replaced before any further use of the instrument. This is an essential part of ownership.

Calibration equipment typically includes a cylinder of calibration gas, regulator and a device to introduce the gas directly to the sensors without mixing it with ambient air. Most direct reading monitors on the market have programmed calibration routines. The programming calibrates the monitor and signals the user when the routine is finished. Always follow the manufacturer’s suggested calibration schedule. Sensors have a routine life cycle of 18 to 24 months. Do not buy sensors ahead of time. Buy them when the old sensor is close to replacement. Always calibrate the unit after a new sensor is installed.

Detection instruments must be calibrated correctly. This is the only way to safeguard against false positives, false negatives, or incorrect measurements of target chemical compounds.

Things to Remember

Remember that when you zero a monitor the electrical output of the sensor at that moment becomes the point of comparison. This can lead to readings that are lower than the actual concentration present. Sensors require a certain period of time to warm-up or stabilize when the monitor is first turned on. Some types of sensors require only a few moments to stabilize while some may take several minutes. All calibration results must be documented for a number of reasons. Should your air monitoring results ever be called into question in a court of law, you can rest assured that the calibration records will be subpoenaed by attorneys. Calibration records also allow you to plot the performance of your sensors and accurately forecast when they will have to be replaced.

The best equipment in the industry is useless if it is being used by someone who is not familiar with its operation. When meters are used by well-trained personnel, they can make the difference between success and costly failure. Gaining proficiency in meter operation is neither costly nor time consuming. A person or select group of people must be responsible for meter calibration and maintenance. This prevents too many people from messing with the internal operations of the meter. As sensors get old, get used a lot or are exposed to large concentrations of materials, their performance will be negatively affected. There is no magic meter that will tell you exactly what to do. Meters only provide data. It is the responsibility of the operator to interpret that data and make the appropriate decisions and take the necessary actions.

Many meters can be plugged into an outlet and trickle charged to ensure that the meter is always charged and ready to go. This requires rechargeable batteries. Regular batteries can be used in the meter but they CANNOT be recharged. This will cause the batteries to explode and damage the meter, possibly beyond repair. Extra batteries on hand will prolong the life of the meter particularly on longer lasting incidents. Remember no currently available instrument can be used as a catch-all that can detect everything. Operators should be well trained in the proper use, limitations and maintenance of instruments. Sensors are designed to work within a certain range. Extreme temperatures — hot or cold — and humidity — too dry or too wet — can negatively affect sensor performance.

Purchasing Considerations

The meter that you select must be reliable, both in operation and the accuracy of readings. The meter must be easy to operate and carry in full PPE, not just bare hands. Routine maintenance and calibration must be able to be performed by someone in the field as opposed to constantly sending the unit back to the manufacturer. It must also be able to be used in a potentially flammable atmosphere without the risk to responders. Some departments carry calibration gas on the unit with the meter while others leave it at the station. This is a departmental preference. You must have a good working relationship with your vendor. Do not buy a meter just because it is the cheapest or because they are going to throw in a few “extras.” If you’ve never dealt with the vendor before, check them out and ask for references. Instrument capabilities will vary from manufacturer to manufacturer.

Data logging is the ability of the monitor to continuously record the data from the atmospheric sampling. The user may then download the data to a computer. Software can then create charts, graphs and tables from that data for exposure records, incident reports and compliance reporting.  Before you buy a meter, test several units and expose them to a variety of materials to see how they react.

Firefighter safety is our number one priority and using air monitoring and sampling equipment will enable the Incident Commander to evaluate the conditions that are present and set acceptable working conditions for our firefighters.

Mark Schmitt is Captain/Hazmat Specialist for the Greensboro Fire Department in Greensboro, N.C., and a veteran of over 20 years in the fire service. The majority of his career has been spent in special operations. He is a graduate of the National Fire Academy’s Executive Fire Officer Program and holds a Master of Public Administration in Emergency Management. Schmitt has taught numerous hazardous materials courses for the Greensboro Fire Department, local community colleges and the North Carolina Office of the State Fire Marshal in addition to serving on several hazardous materials related committees at the local and state level.

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