Understanding Multi-gas Monitor Readings - The Importance of 

Knowing your Equipment

RECOMMENDATIONS

The NIOSH Fire Fighter Fatality Investigation and Prevention Program 

(FFFIPP) recommends fire departments ensure all firefighters responding to 

natural gas and propane incidents are trained to:

 Interpret data from their specific multi-gas monitors to determine if 

a hazardous atmosphere is present. This can include low oxygen 

levels or dangerous concentrations of carbon monoxide, hydrogen 

sulfide, or other toxic gases.

 Calibrate and maintain gas detection equipment properly by 

performing bump testing at the beginning of each shift following

manufacturer’s guidance.

 Use of gas detection equipment under a wide variety of conditions 

including when at the lower explosive limit (LEL) and upper explosive

limit (UEL) of a gas or vapor.

 Utilize multi-gas monitor readings to establish isolation zones and 

ensure a continuous risk assessment is conducted throughout the 

incident.

QUESTIONS & ANSWERS on p. 2

FFFIPP INVESTIGATION 

On July 10, 2018, a 34-year old paid-on-call fire Captain died, and another firefighter was injured in a 

building explosion while responding to a report of a natural gas leak. At 1820 hours, the local combination 

fire department was dispatched for a report of gas odor at an intersection approximately one block away 

from the fire station. The initial arriving crew immediately began evacuating the surrounding buildings. The 

Captain, along with firefighters from the initial responding crew, entered a building near the suspected 

leak to control utilities in the basement. Firefighters reported the gas monitor showing high levels of 

explosive gas. As the crew was exiting, the building exploded. While misreading a gas monitor was not 

contributing factor in this incident, it still highlights the dangerous nature of natural gas leaks. Inadequate 

training on gas monitors puts firefighters (especially hazardous materials teams) at risk. Details of this 

incident are available in the full NIOSH report.

Firefighter Using Multi-Gas Monitor

Photo Credit: Chief Jerry Knapp
QUESTIONS & ANSWERS

What gases do multi-gas monitors detect? 

Firefighters and hazmat teams use multi-gas monitors to measure a variety of different gases in the environment. 

These gases usually include oxygen (O2), carbon monoxide (CO), hydrogen sulfide (H2S), as well as a range of 

flammable gases and vapors (to determine the LEL.) Users must understand that the LEL may not be completely 

accurate as the calibration gas and the gas or vapor encountered at the incident scene will respond differently to 

the monitor (i.e. methane calibration gas vs.propane gas being measured as the incident scene).

What do LEL and UEL mean? 

The LEL is the minimum concentration of a gas or vapor in air below which propagation of a flame does not occur 

in the presence of an ignition source. The UEL is the maximum concentration of flammable gas or vapor in air 

above which propagation of flame does not occur on contact with a source of ignition. The range between LEL and 

UEL is the flammable range. The UEL is extremely hazardous as it may displace oxygen creating an IDLH 

atmosphere and in the event fresh air is added the atmosphere could move into the flammable range. 

Why is bump testing, routine calibration, and maintenance needed? 

Sensors become less accurate over time due to a wide variety of factors including mechanical impacts (e.g. drops), 

dirt/dust that can block the sensor inlets, and extreme environmental conditions such as heat. Users can mitigate 

this with bump testing, routine calibration, and sensor replacement in accordance with the manufacturer’s 

recommendations. Firefighters should follow the manufacturer’s use and maintenance recommendations to 

ensure monitors will operate as intended. Calibrate monitors at least monthly to ensure accuracy. 

What can emergency responders do to ensure personnel understand proper use of multi-gas monitors and how to 

interact with public utilities or specific propane retailers? 

Fire departments and emergency responders should conduct regular hands-on training so firefighters can become 

proficient with their department’s unique multi-gas monitors and the manufacturer’s recommendations. NIOSH 

recommends departments partner with utility companies when conducting training to better understand each 

responder’s role when arriving on scene of a natural gas or propane emergency. This training should be part of a 

department’s standard operating procedures/guidelines for responding to hazardous materials calls.

Where can I find more information about responder competencies needed to respond to a hazardous materials 

event? 

National Fire Protection Association consensus standard NFPA 470. Hazardous Materials/Weapons of Mass 

Destruction (WMD) Standard for Responders, provides the minimum requirements for personnel responding to 

hazardous materials incidents

Find NIOSH products and get answers to workplace 

safety and health questions:

1-800-CDC-INFO (1-800-232-4636) | TTY: 1-888-232-6348

CDC/NIOSH INFO: cdc.gov/info | cdc.gov/niosh

FFFIPP: cdc.gov/niosh/fire/

DHHS (NIOSH) Publication No. 2022-155

DOI Number: https://doi.org/10.26616/NIOSHPUB2022155. August 2022

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