Survival Tip 1 – Calibration of Atmospheric Monitors
By Steven De Lisi
As a first responder, you respond to a call during the evening to investigate a carbon monoxide detector activation that has alerted the occupants of a single family residence to the possibility of a dangerous condition involving this deadly gas. While on scene, you evaluate the atmosphere inside the residence using the atmospheric monitor assigned to your apparatus. Based on your readings, you determine that the building is safe for reentry and you allow the occupants to return.
Early the next morning, an ambulance responds to the same location for several people who are not feeling well. Shortly after these patients arrive at a local hospital, hospital personnel determine that all are suffering from exposure to excessive levels of carbon monoxide. During a subsequent investigation of this incident, investigators determine that the atmospheric monitor you used the day before was incapable of providing accurate readings since it had not been calibrated for quite some time. In fact, no one in your department can remember the last time the instrument was calibrated or who performed this task. There is no written record of this calibration other than an adhesive label on the side of the instrument, but the writing on this label is now worn and illegible.
Lawyers for the residents claim that fire department personnel using the atmospheric monitor were negligent because they did not properly maintain this piece of equipment. A lawsuit naming all fire department personnel on scene that evening as defendants as well as the fire chief is pending.
Could this type of incident happen to you? You bet! To avoid this problem, remember that all atmospheric monitors require routine maintenance, including calibration, to determine the ability of the instrument to delivery accurate readings. Most atmospheric monitors are subject to “calibration drift,” which occurs as the signal output of sensors changes due to routine use and normal degradation over time. Misuse and abuse of these instruments can also alter signal output.
As a general rule, all atmospheric monitors should be subjected to a functional (bump) test prior to each use to ensure that they operate as intended. During a bump test, a device is exposed to a “calibration gas” where the concentration of the gas is known. The device must respond with an acceptable reading.
For example, if you are attempting to conduct a bump test on a carbon monoxide detector and the concentration of this material in your calibration gas is 50 ppm, then the device should display an identical reading. However, the manufacturer of the device may provide an allowable tolerance for a reading that is greater than or less than a certain percentage. For example, using the previous reading of 50 ppm, a manufacturer’s tolerance of plus or minus two percent would allow for acceptable readings that range from 49 to 51 ppm. Any readings above or below these levels would mean the device failed the bump test.
Remember that whenever you conduct a bump test, the concentration of the calibration gas used should be high enough to cause the instrument alarms to activate to ensure this component of the detector functions as intended. During a bump test, there is usually no means to make any adjustments, so if the readings are unacceptable, a full calibration will be necessary.
A full calibration is similar to a bump test except that the instrument readings can be adjusted to coincide with the known concentrations of the calibration gas. In addition to performing full calibration whenever an instrument fails a bump test, perform full calibration on a regularly scheduled basis, such as every 30 days, as well as after any repairs, including the replacement of sensors. The manufacturer of your atmospheric monitor will also provide its recommendations for calibration frequency.
Proper training of personnel who conduct any calibration activities is essential, as is having access to the correct calibration equipment, which is usually available from the instrument manufacturer. It is also important that any calibration be conducted in an environment similar to the one where the instrument will be used. Such considerations include altitude, temperature, and humidity. Instruments should also be “zeroed” before calibration to provide for more accurate results.
The specific concentration of calibration gas used can vary depending upon the manufacturer of the gas. If a different supplier of this gas is used, first responders should be sure to check the new concentration and adjust the monitor accordingly. This is important because a monitor must recognize the concentration of each calibration gas used in order to determine if the monitor either passes or fails the calibration process. For multi-gas detectors, cylinders that contain a combination of all gases to be measured by the instrument are often available.
First responders should remember that most calibration gas is sold with an expiration date. Any attempts at calibration after that date may not only provide inaccurate results but may also subject first responders to greater legal scrutiny if the performance of their atmospheric monitors is ever called into question.
Finally, thorough documentation of test results from both functional and full calibrations is a must. If you use a computer to maintain these records, remember to back up this information. First responders never know when they will need to produce this documentation in court
When using atmospheric monitors, be smart, be safe and remember everyone goes home.
At your next drill, use the following questions for a discussion about the meters your company carries:
- Does your department have a policy on conducting functional calibrations before each use of an atmospheric monitor? If so, are personnel properly trained and do they have access to calibration equipment for conducting these functional tests?
- How often is a full calibration of these instruments conducted? Are these tests conducted in-house or are the instruments sent out to a vendor or manufacturer for full calibration?
- How are calibration records maintained?
- When conducting a functional calibration, do you know the allowable calibration tolerance for your atmospheric monitors?
- If you are responsible for conducting instrument calibrations, do you know the expiration date of the calibration gas you are currently using?
Steven M. De Lisi is Deputy Chief for the Virginia Air National Guard Fire Rescue located in Henrico County and a 26-year veteran of the fire service. He has served as a company officer for the Newport News (VA) Fire Department and as a regional training manager for the Virginia Department of Fire Programs. He is a certified Hazardous Materials Specialist and previously served with the Virginia Department of Emergency Management in the Technological Hazards Division. De Lisi is currently chairman of the Virginia Fire Chiefs Association’s Hazardous Materials Committee and a former member of the National Fire Protection Association’s committee on Hazardous Materials Protective Clothing.