As a one-stop service point for the public in various emergencies that may occur in the world, the fire department must have a large amount of knowledge, skills, abilities and equipment. We use these knowledge, skills, abilities and equipment to help us every day. citizen. We use some equipment every day and use it skillfully, while other items are locked in our minds, and our trucks are pulled out in the rarest cases.
Experience tells us that whether something is used frequently or only once in our career, continuous training is essential to our operational success. Just because we use our defibrillator more than a dozen times a day does not mean that we can skip 12-lead and cardioversion courses. On the other hand, we need to ensure that our technical rescue skills will not rust. Although many of us use our multifunctional gas meters to detect gas leaks and carbon monoxide (CO) detection every day, in the context of some actual events and hypotheses, these instruments still have much to review.
The multifunctional gas meter is the ultimate symbol of daily hazardous goods response. When we are dispatched to daily dangerous goods calls (such as CO alarm sounding), our dispatch, rescue/public protection operations, environment, container, chemical (DRECC) assessment is quite simple. In the winter, a large-scale rescue was dispatched to a residence to obtain a carbon monoxide warning. The size of DRECC is adjusted as follows:
Scheduling: 101 West Street activates the CO alarm.
Rescue/Public Protection Action: Upon arrival, residents may need to be evacuated.
Environment: Indoors in the house in winter.
Container: The heating system, stove or water heater may be malfunctioning.
Chemistry: Reported as CO from residential detectors.
With the aging of the heating system, it is not uncommon to receive too many carbon monoxide warnings in the winter in New England, so it will not bring red flags to company executives. The fire department knows and understands that the substance is a toxic and flammable gas that is colorless, odorless, and lighter than air. The compound is a chemical asphyxiant that can replace oxygen (O2) in hemoglobin.
Officials on the way are preparing multiple gas meters. Many times, the CO level is zero and the homeowner must resolve the detector battery or power supply problem. Sometimes dispatch involves reported symptoms such as headaches and dizziness; response needs should include more companies and medical units.
Departmental policies and procedures usually have a certain level of action, if the level approaches or exceeds the exposure limit (REL) recommended by the National Institute of Occupational Safety and Health (NIOSH) or the allowable exposure limit of the Occupational Safety and Health Administration (OSHA) (PEL). In this case, when the company entered the site, the O2 sensor reading was 20.9% of normal atmosphere; the reading on the first floor was 60 parts per million (ppm).
The homeowner met with the company on the front lawn and reported that they had recently completed work on the heating system. The company put on SCBA during their initial readings and investigated the basement, and they found that the reading near the heating system was 150 ppm.
They turned off the heating system and ventilated the home, and now their reading is zero. Homeowners need to find shelter at night and contact the company that works for their heating system.
All firefighters may be familiar with this situation. Usually, in a medical call, the caller’s symptoms are ultimately due to exposure to hazardous materials.
As a rescuer (medical unit), I have been treating a patient at the back of the truck. Suddenly my SpCO reading popped up on the defibrillator. The SpCO was 12%; the person explained that he was only smoking. It makes sense. The SpCO readings of people I have recently smoked hookah have also been very high.
In other cases, patients will experience high SpCO without a reasonable explanation. Then, the company will check the carbon dioxide in the house to ensure the safety of other residents.
A few years ago, we received a call saying that someone complained about dizziness. He was working on a damaged foundation in the basement and began to feel dizzy. He felt better when he walked outside, so he went back to work in the basement. In the basement, his symptoms reappeared and he requested emergency medical services (EMS) to respond. After hearing this story, the engine company measured the basement and found that there was a lack of oxygen in the air. At first, there was no obvious reason for this lack of oxygen in the atmosphere. The next step is to use auxiliary meters and test tubes to confirm this discovery. Both meters display an atmosphere with insufficient oxygen, and a test tube dedicated to O2 supports the content displayed by the meter.
Our Deputy Director of Dangerous Goods was called to the scene and after doing some research, a carbon dioxide (CO2) detection tube was used. The tube shows that carbon dioxide is replacing the oxygen in the basement. This is the reason why the workers have symptoms. Further research shows that sometimes CO2 can seep out of the soil from the decaying material, and on the basis of damage, it will enter the basement of this home.
On another occasion—ironically, when officials were teaching dangerous goods to the recruits class—the fire department's carbon monoxide alarms started to sound in the administrative office upstairs, our training room, and the dispatcher. The heating system is not operating because the weather is relatively warm. We walked around the building with a multifunctional gas meter and carbon dioxide sensor, and the reading was 30 to 40 ppm. Then we took out the detection tube and tested it in the dispatch room, administrative office, and training room; our CO was 0 ppm.
We need to figure out why a meter designed to detect CO is in an alarm state. Some sensors are cross-sensitive; they activate when something other than the expected material is present. After further investigation, we learned that the maintenance department on the first floor accidentally cracked their acetylene tank slightly, and everything was reasonable. Acetylene is a known cross-sensitive material for CO sensors; because it is lighter than air, it found its way to the office upstairs. We turned off the water tank, ventilated the building, deactivated the station detector, and our meter read zero.
A full understanding of the purpose and limitations of the instrument is essential for the safety of the public and firefighters responsible for daily hazardous materials accidents. Understanding the type of technology in the meter is not as important as understanding its calibration gas, how it affects the readings we see in the field, the application of correction factors, the level of action required by your department’s policies and procedures, the meter’s reading limits, and its performance. Under the conditions, and its cross-sensitivity, and use a variety of techniques to confirm all readings. The following explanation is for the brand of gas detectors used in our department.
For many historical reasons, gas detector sensors are calibrated using the gases we use today, but the most important thing is to understand how this affects the response of the instrument. Our specific meters can usually measure O2; Lower Explosive Limit (LEL); and Volatile Organic Compounds (VOC), which are representative of photoionization detectors (PID), CO, and hydrogen sulfide (H2S). All our fire fighting equipment and battalion commanders are equipped with these meters.
The H2S sensors on some meters have been replaced with hydrogen cyanide (HCN) sensors for use during post-fire inspections. Gas detection companies have begun to provide multi-gas meters with four, five and six sensor slots (photo 1). We recently purchased a six-gas meter equipped with both H2S and HCN sensors.
Advances in technology allow the use of GPS to track meters and transmit the data back to the command post computer in real time. Some even have the function of people falling to the ground, which can send the SMS distress signal to the designated phone list, or directly contact the user through the meter. In addition, some newer meters can read gamma radiation (photo 2). If you use one of these meters in an accident, remember that the pump will run for 50 seconds to measure air and stop for 10 seconds to read gamma radiation. Within 10 seconds, you may walk into a higher concentration of gas without seeing an upward trend until the pump resumes measuring air.
If the gas is unknown due to the different vapor density, please remember to measure the floor, middle and ceiling of the room. Respondents should know the vapor density of the most common chemicals encountered. CO, natural gas, and HCN are lighter than air and need to be metered in the upper part of the room or structure. H2S, propane gas and chlorine gas are heavier than air and need to be metered at a lower level. All this can be traced back to our comprehensive assessment of what should and shouldn't appear in a given scenario after our scale adjustment.
Sensors designed to read specific chemical substances are calibrated for that gas. Sensors designed to read multiple chemical substances have a specific calibration gas, and when you know that the gas in the atmosphere is being measured, you will read it directly. If the sensor can even detect them, all other substances require correction factors.
Most multifunction gas meters will prompt the user to perform a "fresh air calibration" during their startup, or the user can access this option in the calibration section of the menu. Other instruments have specific buttons to perform this operation at will. This allows the meter to zero the sensor. Make sure that the air is actually fresh before performing this calibration, otherwise the readings will be biased. For example, do not perform a "fresh air calibration" near the exhaust port of a truck.
LEL and PID sensors are the most important. The LEL sensor is calibrated for methane gas, which is the main gas in natural gas. Since natural gas is used for cooking and heating, we all respond to natural gas emergencies on a regular basis. Therefore, our LEL sensor calibrated for methane gas allows direct reading in natural gas emergency situations. It must be remembered that the LEL sensor reading is a percentage. The sensor is calibrated based on the LEL of methane, which is 5% or 50,000 ppm.
In an environment where the LEL sensor reads zero, this does not mean there is nothing. Since the sensor only displays whole numbers, you won't find 1% on the meter until the methane gas setting reaches 500 ppm or 1% of 50,000 ppm. Gases may be both flammable and toxic; generally, toxicity and damage to the body occur at levels significantly lower than the LEL. Therefore, when the LEL sensor reads zero, a 450 ppm substance may be fatal.
Consider anhydrous ammonia. It takes 150,000 ppm of this gas to ignite in a confined or enclosed atmosphere, but its immediate danger to life or health (IDLH) level is 300 ppm!
In addition, when responding to a natural gas emergency, do not confuse the reading on the LEL sensor with the gas company's meter reading. The meter of the gas company is not set to the LEL of methane.
For example, if the natural gas content of a house is 50,000 ppm, and our meter reads 100%, and the gas company's meter reads 5%. This is done deliberately, because we are dealing with a large number of dangerous goods incidents, and it is not just natural gas that needs to be safely measured. Knowing when we are close to LEL is critical to our safety.
PID is read in ppm. Some of the latest technologies will start with readings in parts per billion (ppb), as shown in the VOC reading in Photo 3, and then automatically switch to ppm as the concentration increases. PID is usually expressed as VOC on the meter's screen-this is misleading because the sensor can also detect inorganic compounds. The sensor is calibrated with isobutylene and can detect concentrations as low as 0.1 ppm. This sensor is suitable for toxicity issues, and we must be able to read the lowest possible concentration.
For example, benzene is commonly found in petroleum products, and its NIOSH REL is 0.1 ppm, which is a known carcinogen. A detailed list of what these sensors can measure is available online, but it should also be printed out and saved in a binder. This becomes important for applying correction factors or knowing whether the meter will detect the substance.
To reiterate, just because the meter does not read the substance does not mean that nothing exists! Respondents must rely on their judgment of the situation, the type of incident/occupancy, which chemicals should be present, which should not, and those exposed to their symptoms to drive their incident action plan.
The technical instructions of the detector manufacturer are available online; when LEL and PID sensors read known substances, you will need to use them. You will need additional technology to further classify any unknown substances that produce meter readings; the responding dangerous goods response team or dangerous goods technician is responsible for this.
Also, please understand that PID sensors have specific lights. These sensors use light to ionize matter; the different lamps available provide different amounts of energy. The different lamps listed in the PID sensor technical description of our detector manufacturer are 9.8 electron volts (eV), 10.6 eV, and 11.7 eV; each lamp can detect a list of specific chemical substances. When researching a chemical, if its ionization potential is 9.67 eV, then any lamp can measure (ionize) the compound; if the ionization potential is greater than 11.7, no lamp can read the substance.
In our department, our PID sensor uses a 10.6 eV lamp, so the sensor cannot see the chlorine gas, and its ionization potential is 11.48 eV. However, we can measure anhydrous ammonia (NH3), but in order to get an accurate reading, we need to use the technical description to apply the correction factor. If we enter the NH3 atmosphere and our VOC reading is 100 ppm, the listed correction factor is 10.9, which will provide a corrected reading of 1,090 ppm ammonia.
In photos 4 and 5, the detector is not a multi-gas meter; it is a dedicated PID with a library, so if a chemical substance is known and it is in the library, you can change to that chemical substance and then no correction factor is required.
The same is true for LEL sensors, we will check the list in the manufacturer's LEL technical description to see if the chemical we are trying to measure is present, and then multiply the reading by the correction factor. For ammonia, if the LEL sensor reads 10%, the correction factor is 0.9. After multiplying the reading by the correction factor, we are actually at 9% of the ammonia LEL.
The action level determines how we will respond based on the readings provided by the meter and how we interpret the readings and data. Based on materials, regulations, consensus standards or your organization's standard operating procedures (SOP) will determine your level of action. Industry and emergency response use action levels in the form of exposure limits, which are concentrations set by the industrial hygiene community to determine the level of personal protective equipment (PPE) required in the presence of a given substance. Below the exposure limit, no PPE is required.
For example, for carbon monoxide, NIOSH sets the REL of CO to 35 ppm; at or below this level, PPE is not required for an eight-hour working day and 40-hour weekly exposure. This is our department’s CO response SOP: at 35 ppm or below, we don’t need to broadcast live, but responders above this value must wear a mask and continue live broadcast. The only personnel who should operate above the exposure limit are those who have received metering and training in chemical protective clothing and respiratory protection. If the concentration of a given compound exceeds the IDLH level, only qualified personnel can operate in this environment.
HCN is another substance for which we have established an action level SOP. We also measure after fire extinguishing, maintenance, and ventilation; the HCN level must be zero to allow anyone to enter the structure without an air breathing apparatus. Due to the numerous structures of hazardous compounds caused by fires, we are revising and expanding this policy. The best strategy to maximize the long-term health and well-being of the fire department is to use respiratory protection when operating in a toxic environment.
In addition to CO and HCN, a variety of toxic, carcinogenic and corrosive chemicals may be produced in the combustion structure. Some toxic gases are also corrosive, including ammonia, hydrogen fluoride, hydrogen chloride, and formic acid. In dangerous goods accidents, the presence of these gases requires Class A protection, which further emphasizes that wearing respiratory protective equipment during inspections is essential to the health and safety of firefighters.
Some additional toxic gases are also carcinogenic, including acetaldehyde, acrolein, acrylonitrile, benzene, formaldehyde, glutaraldehyde, isocyanate, naphthalene, nitrogen oxides, sulfur dioxide, toluene, and vinyl chloride. There must be more compounds; this list of chemicals comes from the technical description of the detector manufacturer's overhaul library. The equipment provides different libraries depending on the operation: weapons of mass destruction, toxic industrial chemicals, secret laboratories or overhauls. When it detects a substance in the overhaul library, it will sound an alarm and visually remind the user to "disguise" the time-weighted average (TWA) level if it detects any of the chemicals listed above. Although the meter will not visually identify a specific compound, it will tell the user to "mask" if it detects a chemical substance in the library; if the detected substance is not in the library, the display will display "Detected chemical substance" "(Photo 6).
Departments should adopt policies to deal with structural and vehicle fires, such as dangerous goods scenes, and actively carry out metering, ventilation and respiratory protection after they occur. Decontamination is another aspect that is often overlooked in post-fire operations. My department has improved in terms of purification after fire operations in the past few years. Initially, you should be decontaminated on site, and then return to the dormitory more thoroughly to clean the equipment with a suction device. Setting up and performing decontamination at the hazardous material site has been included in the OSHA standard, so it is always implemented. After exposure to combustion products, the fire department needs to change to a culture of forced purification. Whether in a dangerous goods accident or a building/vehicle fire, having a healthy professional life and long-term retirement to protect yourself from chemical exposure is essential.
When measuring the space, the O2 concentration must be between 19.5% and 23.5%; concentrations below 19.5% or above 23.5% are considered IDLH atmosphere. In most spaces, O2 is usually 20.9%. Oxygen accounts for one-fifth of the air in our atmosphere. Why is this important? If we measure a space, the reading starts at 20.9% O2, and as we continue to enter the facility, O2 rapidly drops to 19.9%, which means that 50,000 ppm of gas has replaced air—including its O2. Then, we must try to figure out whether and why there is a gas replacing O2, such as CO2, at this location.
Although rescuers can use SCBA in an O2 deficient atmosphere, protecting it in an O2 rich atmosphere is more challenging. In this case, ventilate the space and reassess how the oxygen-rich environment is created. In the above-mentioned residential basement, where carbon dioxide replaces oxygen, we use SCBA to protect ourselves, and we use multiple technologies to measure the space.
An important operating level to remember involves LEL sensors. The action level of the LEL sensor is 10%. If it is a natural gas emergency and we know that our meters are calibrated for methane, then we will not be at a 10% risk, we can continue to locate the source of the leak and try to mitigate the leak while ventilating. The manufacturer's technical specification for the LEL sensor includes a long list of detectable compounds. When dealing with unknown atmosphere, our action level is 10%, because below 10% we can be sure that it is safe to continue metering, but at 10%, we must stop, exit, ventilate and reassess. The correction factor of some chemical substances that the LEL sensor can detect is above 5; if we push the limit to 20%, we may reach or exceed the LEL of the substance and put ourselves in extreme danger.
Depending on the scenario and associated risks, the incident commander may approve operations above the 10% LEL action level. However, please consider other strategies to reduce the risk to responders, including ventilation, adjusting the size and location of personnel, and the placement and use of hoses. Adopt and train departmental policies to set action levels in hazardous material incidents to maximize the safety of responders.
Each sensor has its own specifications, which are included in the instrument manufacturer's technical description. Our manufacturer provides the following information:
In the fire service, equipment malfunctions, the battery is dead, and the truck's charging device is short-circuited. Now you can't use one of the most important instruments. Even if the meter works well initially, it sometimes fails-poor meter performance, dirty pumps, clogged filters, accidental changes to settings, or sensors that need to be replaced.
Multi-gas flow meters are sampling the atmosphere and running on four to six sensors at the same time, and rely on computer programs to provide accurate results. Our department broke down on site. If you are lucky enough to have access to multiple meters, please deploy multiple units on site to ensure accurate readings.
Please also note that some samples may damage the meter. For example, the meter is not designed to suck in liquid, but the user accidentally sucked a sample of the liquid into the meter, thus damaging the sensor and pump. Corrosive gases (ammonia, acid gases) can also damage the meter.
In order to provide monitoring redundancy, multiple monitoring units are used when dealing with unknown atmospheres. This is one of the reasons why the hazardous materials response team will also use simple chemicals (such as pH test paper or test tubes) compared to technology. If responders are well-trained in responding to hazardous materials, these easy-to-use items can confirm what the meter is telling us or exclude certain compounds, just as we did when the CO detector was activated at the fire station. If you cannot use alternative dangerous goods detection devices or technologies and can only use one multi-gas flow meter, please make sure to calibrate and repair it as planned to ensure that it can be used whenever needed.
Compounds that we can't see or smell pose a major risk to our health and safety. The daily life of human beings relies on equipment that uses explosive gas; if it fails, it will produce deadly gas. Testing equipment can save lives. Metrology expertise will ensure the safety of firefighters; confirm that we have mitigated the impact of the incident; and, most importantly, let us inform the public that they are safe.
Understanding the complexity of our meters ensures that we deploy them correctly and accurately interpret their data to help drive operations, regardless of the size of the incident. Even if a department is not equipped with a dangerous goods team and must rely on regional dangerous goods to respond, the initial company will handle the public’s first calls when people are sick, detectors are activated, and unusual odor reports are reported. Mastering the use of multiple gas meters will undoubtedly make all responders responsible for mitigating the harm of these incidents and improving the quality of services we provide to citizens.
Richard C. Beaulieu is a lieutenant in Cranston (RI) Fire Department (CFD) Rescue 2 and has been serving there since 2008. He has worked in the fire department for 15 years and has a Bachelor of Science in Fire Science from Providence College. Beaulieu has been a dangerous goods technician since 2006, is an NFPA 1041 certified lecturer, and is responsible for coordinating the training of dangerous goods technicians at the CFD Recruit Training Academy.