Simulated Smoke, Real Health Effects


In 2011, a fire training facility used by approx- imately 255 full-time firefighters and five full-time trainers contacted the National Institute for Occupational Safety and Health (NIOSH), an agency within the Centers for Disease Control and Prevention (CDC), for assistance. During preparations for a training exercise, three trainers without respiratory protection had been exposed to a cloud of oil-based smoke simulant for at least 30 minutes. The trainers reported respiratory symptoms such as coughing, shortness of breath, difficulty breathing, and chest tightness. Two of the trainers improved, but one worsened and was hospitalized for a week with chemical pneumonitis/lipoid pneumonia. Many of the firefighters and trainers had been under the impression that the smoke simulants were not hazardous. After this incident, they became concerned about the effects of exposure to the chemicals in the smoke simulants and asked NIOSH to conduct a health hazard evaluation.


The facility conducted training exercises designed to teach fire attack and victim rescue techniques under low-visibility conditions inside a three-story concrete tower (photo 1). Some exercises involved only smoke simulant (photo 2), and some involved smoke simulant and heat (photo 3). Propane burners produced the flames that generated the heat, which was intended to create rollover fire conditions with temperatures of more than 400°F. Two types of fog machines were used to produce the smoke simulant. A built-in system generated a mineral oil-based simulant, and portable fog machines generated a glycol-based simulant. Trainers were responsible for preparing the rooms in the training tower for the exercises; checking the room conditions prior to the exercises; directing the exercises from inside the room, usually while wearing respiratory protection; and venting the tower once the exercises were complete. Trainers typically wore respiratory protection including self-contained breathing apparatus (SCBA) for exercises involving heat and smoke simulant and N-95 filtering face piece respirators for exercises involving only smoke simulant. Occasionally, trainers without respiratory protection opened doors and looked into the smoke-filled rooms.

Photo 1
Photo 2
Photo 3
Photos courtesy of NIOSH.
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We took area and personal air samples during six training exercises and tested them to determine to what contaminants the trainers were exposed and in what concentrations. For each exercise, area air samples were collected at a point one to three feet above the floor in the middle of the room, where trainers would kneel, and five feet above the floor outside the training room door, where trainers would stand to check room conditions. In addition, we collected personal air samples just below each trainer’s SCBA mask while the trainer was inside the training room. Researchers took other area air samples from different locations inside the rooms during certain exercises to measure particle size. Two exercises involved only oil-based smoke simulant; one involved only glycol-based simulant. Because certain chemicals break down with heat and may generate different exposures, we also collected samples from an exercise involving oil-based simulant and heat, another involving glycol-based simulant and heat, and one more involving oil-based and glycol-based simulants and heat. For the last exercise, we also tested the effect of height on contaminant air concentrations.

For this evaluation, we compared the air testing results to occupational exposure limits, in particular, the excursion limits for exposure to hazardous substances set by the American Conference of Governmental Industrial Hygienists (ACGIH) and the American Industrial Hygiene Association (AIHA), as well as ACGIH and NIOSH ceiling limits. Air concentrations should not exceed the excursion limits or ceiling limits even for a short time. When different organizations had different occupational exposure limits, we chose to use the most protective (lowest) limits. The exposures in this evaluation were measured over a period of 15 minutes, which is the time it normally takes to complete each training exercise.

Because it is impossible to test for all potential contaminants, we focused on those most likely to be generated in the exercises. The testing methodology and the full sampling results are contained in the Health Hazard Evaluation (HHE) report “Evaluation of Chemical Exposures During Fire Fighter Training Exercises Involving Smoke Simulant” at This article summarizes the report’s findings.


Oil-based simulant. For exercises involving only oil-based smoke simulant, samples inside the training room showed exposures to mineral oil mist above its exposure limit. Oil mist concentrations measured outside the room also exceeded this limit with the door open but were well below the limit when the door was closed. The highest concentrations of oil mist were measured nearest the discharge nozzle of the fog generator within the room. The oil mist particle sizes were small enough to penetrate deeply into the lungs if inhaled without respiratory protection.

Simulant and heat. For the exercise involving oil-based simulant and heat, concentrations of oil mist, formaldehyde, and acrolein were above their limits. Oil mist and formaldehyde concentrations were above their limits even outside the room with the door mostly closed.

Glycol-based smoke simulant. For the exercise involving only glycol-based simulant, exposure to diethylene glycol was above its exposure limit inside the room and outside with the door opened. These particles were also small enough to penetrate deeply into the lungs. Formaldehyde was found inside the room at concentrations above background levels but below its limit.

Simulant and heat. For the exercise combining glycol-based simulant and heat, concentrations of diethylene glycol and formaldehyde within the room exceeded their limits, and benzene and acrolein were found at concentrations above background levels but below their limits inside the room.

Oil- and glycol-based simulants with heat. For the exercise involving oil-based simulant, glycol-based simulant, and heat together, concentrations of mineral oil mist, diethylene glycol, acrolein, and formaldehyde exceeded their exposure limits inside the room. The training room door was slightly open during this exercise, and the formaldehyde concentration outside the room also exceeded its limit. Mineral oil mist exposure outside the room was at its limit. Concentrations of benzene and crotonaldehyde, which were above background levels but below their limits, were also measured in the room. Because the heat inside the room forced much of the smoke toward the floor, air samples were taken inside the room at two-foot and five-foot heights. Some chemical concentrations were greater at two feet, and some were greater at five feet.


Short-term exposure to inhaled mineral oil mist may result in lipoid pneumonia or chemical pneumonitis. Other effects of exposures include eye, skin, and upper respiratory tract infection; central nervous system effects; and respiratory distress. The trainer who was hospitalized with lipoid pneumonia had been near the supply valve without respiratory protection and was exposed to a high concentration of mineral oil mist over 30 minutes.

Short-term exposure to diethylene glycol may have adverse effects on the blood, liver, kidneys, and central nervous system. Short-term exposure to formaldehyde, acrolein, and crotonaldehyde may result in skin, eye, and respiratory tract irritation, and inhaling high concentrations of these aldehydes may cause pulmonary edema. Short-term exposure to benzene may cause skin, eye, and respiratory tract irritation as well as adverse effects on the central nervous system.

The results of this evaluation show that exposure to the smoke simulants and their breakdown products when heated may exceed exposure limits, which are intended to prevent adverse health effects resulting from short-term exposures. Because of the potential for adverse health effects, firefighters should not be exposed to smoke simulants without appropriate personal protective equipment (PPE), even for brief periods.


Based on the findings of this evaluation, we recommend the following actions to reduce harmful exposures in training exercises involving smoke simulant. These recommendations are based on the hierarchy-of-controls approach, which prioritizes actions based on their likely effectiveness from the most effective to the least effective.

Engineering controls would reduce exposure by removing the hazardous substance from the workers’ environment. Use the training tower’s exhaust system to completely ventilate the structure immediately after completing a training exercise, and do not allow anyone to re-enter the tower without appropriate respiratory protection until all smoke simulant has visibly cleared.

Administrative controls (practices and policies to prevent or reduce hazardous exposures) only work if employers commit to them and workers follow them. Recommended administrative controls for these exposures follow:

  • Rotate training duties throughout a full day of training exercises to reduce each trainer’s chemical exposure. This also lessens the physiological strain associated with repeated training exercises.
  • Encourage trainers to report symptoms or health concerns associated with work tasks to a supervisor. Irritation to the eyes or respiratory system may be the most immediate symptoms a trainer experiences if not adequately protected during training exercises.

-The use of PPE is the final and least effective method in the hierarchy of controls. Users must use the correct equipment for each type of exposure, and they need to be trained to get the full benefit. For some types of equipment, fit testing or medical clearance may be necessary. In general, PPE should not be the only method for controlling exposure. We recommend the following:

  • Wear structural firefighting ensembles, including SCBA, inside the training tower during preparation and execution of training exercises involving heat, even when the trainer is outside the training room and only looks in briefly. The SCBA provides the best respiratory protection against the contaminants we measured as well as others that were not measured but might be present. These ensembles would also provide protection if an emergency occurred inside the training room and the trainer needed to provide assistance. SCBA can also be used for exercises not involving heat, but the added weight increases the physical burden on the trainers.
  • Wear NIOSH-approved full face piece air-purifying respirators with NIOSH-approved cartridges/canisters effective against oil aerosol, glycol aerosol, and formaldehyde during the preparation and execution of training exercises involving smoke simulant (but not heat), even if the trainer is outside the training room and only looks in briefly. Consult the respirator manufacturer to choose the appropriate cartridges/canisters. Combination P100/formaldehyde cartridges may be effective, depending on the makeup of the simulant used. Full face piece respirators will also protect trainers’ eyes from chemical irritants or other hazards. Trainers should be clean-shaven and should check the seal of the respirators before using them. This is especially important for negative-pressure air-purifying respirators because an improper seal will allow contaminated air to leak in.
  • Fit-test full face piece respirators under the configuration in which they will be used.
  • Determine a cartridge/canister change-out schedule based on the service life of the cartridge/canister according to use. Consult with the respirator manufacturer and see the NIOSH HHE report for information and resources on how to determine this schedule.
  • Wear nitrile gloves when refilling fog machine reservoirs with oil-based or glycol-based fluids.
  • Wash your hands at the end of each training exercise and shower at the end of a series of training exercises to rinse any chemicals off the skin.

Firefighting by its nature involves unavoidable dangers and hazardous exposures, which makes it all the more important to take precautions against avoidable ones. Although exercises involving smoke simulant were considered nonhazardous by the trainers, we found that they posed health risks. We encourage firefighter training facilities to use the controls discussed above to limit exposures to smoke simulant and better protect their personnel.

T.M. JACKSON is a technical writer with CACI, Inc.

KENNETH W. FENT, Ph.D., CIH, is a research officer in the Industrywide Studies Branch at the National Institute for Occupational Safety and Health (NIOSH), a certified industrial hygienist, and a lieutenant commander with United States Public Health Service. He has performed numerous evaluations of firefighters’ chemical exposures.

KRISTIN MUSOLIN, D.O., M.S. is a medical officer in the Hazard Evaluations and Technical Assistance Branch at NIOSH.

MARK METHNER, Ph.D., CIH, is a senior research officer in the Hazard Evaluations and Technical Assistance Branch at NIOSH, a certified industrial hygienist, and a captain with the United States Public Health Service.

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