Investigating Strange Odors


One commonly used phrase in firefighter terminology, “smells and bells,” refers to the large percentage of fire alarm and odor calls we respond to. In a way, these are positive situations because more often than not, they turn out to be nuisance calls rather than actual fires, which mean fewer lives lost and less property damaged.

Another positive: For years, we’ve taught the public to call 9-1-1 as soon as they discover a problem, rather than waiting until the fire begins to grow, threatening lives and property. Now, many people are listening to us, which is great–but “problems” that turn out to be nuisance calls can wear on both personnel and equipment.

Today, because people live closer together, particularly in multi-family units, the odors from one residence might easily waft into another, at times causing people to become concerned, even if it’s just an odor that’s not familiar to them. And it can prove quite challenging to determine an odor’s source.

In this article, I’ll discuss how to search for and identify an odor on scene, so that you can identify the source more easily and quickly return to the station to be prepared for your next run

Searching for the Source
Odors that alarm our customers have many causes. One of the most difficult situations occurs when you clearly smell something that’s burning, but can’t locate the odor’s source. Although it can take some time, you must continue searching until you find the odor’s cause or the fire that’s causing the odor reveals itself.

Search tip: When first arriving on scene at this type of call, ask the occupants if they’ve recently used any appliances. Then try to isolate the odor to the room or area that it seems strongest. One primary spot to check: the heating, ventilation and air conditioning (HVAC) ductwork. Checking the HVAC system will help determine if the odor is coming from it or traveling through it from another area. If the odor is coming through the HVAC equipment, you’ll need to trace it back through the system. This will most likely require you to gain access to the HVAC unit itself, which may be in a basement, mechanical room, outside the building or on the roof.

You may also need hand tools to dismantle the cover of the HVAC unit to look inside and locate the problem. One very cold night, our firefighters spent well over an hour searching for a burning paper odor in a house. They didn’t give up the search until they located a service manual that had been left inside the heating unit and had begun to char a bit.

Note: It’s important to remember that firefighters are not HVAC technicians! Do not try to service or repair HVAC equipment. Simply troubleshoot where the fire/odor is coming from, shut down any equipment that’s malfunctioning and recommend that the occupant call an expert to make repairs. In commercial buildings, building maintenance personnel or HVAC technicians may be available on site to assist.

If leaving a property without heat in freezing weather, advise the occupant to safely use alternatives or relocate elsewhere until the system can be repaired. In cases where no heat will be available in freezing temperatures, water pipes may need to be secured and drained to prevent freeze-ups.

Other Appliance Culprits
Besides the HVAC system, other appliances may emit smoke odors, such as the dishwasher. Sometimes, plastic utensils or wooden material may fall to the bottom, coming in contact with the machine’s heating element. This will melt the plastic or burn the wood, causing it to give off an acrid odor that may be difficult to pinpoint if you don’t check inside the appliance.

Another appliance-related problem: self-cleaning ovens. Many consumers don’t realize these ovens clean by burning off residue. As a result, when they see or smell smoke (or flames) and determine that the oven is hot (it’s supposed to be), they call the fire department.

Search tip: In most cases, these ovens have a safety feature that keeps the door locked during the cleaning cycle, so you’ll be unable to open the oven door. Check for any fire extension to surrounding cabinets or areas, paying close attention to napkins or paper towels that may be stored in cabinets connected to or near hot surfaces, and advise the homeowner to confer with the dealer/manufacturer, even though there’s a good chance the unit is functioning as designed. If the homeowner insists the self-cleaning function is a hazard, your only recourse may be to shut down the electrical breaker feeding the unit.

Electrical Issues
Buildings with fluorescent lighting always have the potential for an overheated light ballast. These give off a distinctive odor, but you may find it difficult to determine exactly which light overheated, particularly if you can’t reach them.

Search tip: Visually check the lights for darkening bulbs or one light that appears dimmer than the others. But be sure maintenance personnel or an electrician is on hand to remove any problem unit. Stand by until you can confirm that the light has not ignited the ceiling, as hot ballasts in contact with combustible materials on or above a ceiling have caused numerous structure fires.  A thermal imager can be quite handy in checking for overheated ballasts.

Overheated wiring can also result in odors and will require more detective work. You may need to check the breaker/fuse box to see if any circuits are warmer than others; a thermal imager can help with this. Firefighters should limit their involvement to verifying no fire is present, shutting down appropriate breakers where necessary and referring the occupant to a qualified electrician. In some cases, drywall may need to be removed around “smoked” outlets or other electrical equipment, to verify there has been no fire spread.

Computer Trouble
One major challenge: Electrical odors that have been detected in buildings with many computers. If you’ve ruled out all other sources, such as HVAC equipment, and believe you have a burned-out PC, the best way to locate the odor’s source is to check the functionality of all the equipment in the area. If the building has been evacuated, instruct employees to return to the area in which you’ve isolated the problem and have them turn on all their computers, monitors, printers, etc. Station firefighters with an extinguisher or two (CO2 is best) in the area, and ask the employees to indicate whether their equipment is working.

If you discover malfunctioning equipment, put your nose to it, and if it’s giving off a distinct odor, you’ve most likely identified the source. Unplug the problem unit and remove it from the building to a safe area. Similar tactics can be employed at residences where electrical surges may have occurred and multiple electrical appliances are present. Refrigerators, TVs, and home computers are all susceptible to this type of situation.

To make matters even more challenging, newer types of air-sampling smoke-detection systems that can detect chemicals and other combustible products before you see or smell them are becoming more common. So, you may respond to a smoke detector activation call, and even though you won’t be able to see or smell anything, you’ll know a problem is lurking in the area.

These systems are typically located in computer rooms or other high-value areas, and the cause of the system activation will likely be electrical in nature. Tip: Contact personnel familiar with the equipment so they can check it for any malfunctioning parts. This will likely determine the cause of the problem. A thermal-imaging camera (TIC) could also be very handy in this situation.

FOTS Fires
In multi-family dwellings, smoke odor calls are common around dinnertime, which I have learned from experience can be almost any time of day, but it’s usually between 1700 and 2100 HRS.

The food-on-the-stove (FOTS) odor is an obvious one, but once you arrive on scene, don’t stop searching until you’re sure you’ve found the source. More than one oven/stove fire has extended into overhead cabinets or to the remainder of the kitchen, and at times may include a victim passed out in the area. The offending party may not quickly open their door to you, but you must verify that there’s no extension. Tip: At times, you may want to enlist the aid of your local police department to help convince residents of the value of further investigation.

Problems with debris caught under stove burners, material stuck in toasters or the infamous scorched-popcorn-in-the-microwave scenario are good sources of FOTS smoke odors. Look for traces of scorched popcorn in the microwave or in the trash in office or dormitory kitchen areas. If you find popcorn in the trash, the offender probably discarded the burned remnants of their snack, but an innocent second party entered the area, smelled the smoke and called emergency services. A little detective work on your part can quickly isolate this problem.

Note: Unfortunately, the FOTS smell may not dissipate quickly–it is rather distinctive and persistent.

The Great Outdoors
Mulch odors have become more of a problem over the past decade or so. Freshly spread mulch has a distinctive odor that many city folk aren’t used to, so when the smell translates to the inside of a building, people mistake it for the smell of smoke.

Mulch generates heat as it decomposes, giving off an intense, smoky odor, and it may even begin to smolder or burn, particularly during very hot weather. A discarded cigarette inside the mulch can enhance the degradation process as well as become an ignition source.

Search tip: Check around building air intakes for mulch problems. I’ve seen this particular situation in hotels/motels where each room has an individual HVAC unit mounted under a window, bringing air in from the area immediately outside the room.

Another problem dislocated city folk may encounter when they move: the scent of skunks. Skunk odor is distinctive, but may change as it moves indoors. Ask the homeowners if they recently brought their dog(s) in from the outside, because they can bring the skunk odor in with them. Check in and around heating units to see if a skunk is living there, has just visited there or–worst-case scenario–has decided to end it all in or around the moving parts. If needed, you might suggest the homeowners spend the night somewhere else until they can get someone to deodorize the place.

Firefighters have also been called to properties to investigate a “chemical odor,” only to find the fragrance is being emitted by blossoming trees or shrubbery. My only suggestion: Be sure to involve your most sensitive, tactful crew on this one.

Remember: Keep eyes and ears open, and remain open-minded to unusual circumstances. One rather unusual incident that we handled involved an odor of wood burning inside a house. Three crews checked the home thoroughly for 45 minutes and were unable to locate the source. The homeowner had opened the windows prior to our arrival, and the odor dissipated. Eventually, the odor was tracked down to a window frame in the bathroom that had a swing-out vanity mirror in front of it. The setting sun coming through the window hit the mirror at just the right angle so that the reflected sunlight actually scorched the window frame. Once the sun set, the heat source was removed, and thus the incident never spread beyond the 3″ inch scorch mark on the frame.
Drainage Pipes
Foul odors that smell like sewer gas or a very acrid smoke will most likely be found in a home where the owner has been away for a few weeks or more, in a basement where floor drains get little use, or in a laboratory building. Drainpipes are equipped with U-bend traps designed to prevent odors from traveling back up into the working/ living area. This includes all drain lines from appliances or other equipment. But if the drain hasn’t been used in a while, the trap can dry out, allowing any odors from that waste system to filter back up into the living/working area. This is particularly true for bathrooms or kitchens. You can easily fix this (and look like a real hero at the same time–it may be the easiest win ever) by running water down the drain line, restoring the water seal in the trap and preventing the odors from backing up into the area. It’s quick, easy and effective–the way I like to roll!

Your Nose & Other Tools
There are a number of critical tools you can use when investigating smells and bells calls. One of the most important is a fresh, unclogged nose. If a crew has been investigating one of these types of calls for 10—15 minutes with no success in determining the odor’s source, you may need to bring in different personnel because the initial crew can become desensitized to the odor. That doesn’t mean rolling apparatus with lights and sirens as if the world is coming to an end, but bring the crew in efficiently to help out.

Other important tools include gas meters (where available) and TICs, which are quite useful when checking a large area quickly and when searching for overheated, ceiling-mounted, fluorescent lights that aren’t easily reachable.

A toolbox equipped with a variety of hand tools that can be used to dismantle machinery, such as heating units, appliances, etc., is another useful, investigative tool. Keep at least one extinguisher handy (water or chemical, depending on the hazard), as you want to be ready if you indeed find a fire during your investigation.

It’s almost a guarantee that your fire department will be called to investigate a strange odor at some point. It may not be the favorite call of many firefighters, but we have told the public to contact us, so we need to investigate each call properly. Worst-case scenario: You’re unable to (or just don’t bother to, which is much worse) identify the source of a building odor, and later that day or night, you return to the same location for a working fire. If this occurs, you must have good documentation of the original call and a good lawyer on retainer.

Think now about how you’ll handle these situations, so that when you respond to the “smells and bells” calls, you’re able to quickly and effectively identify the problem and return to service for the next run.

Sidebar: What’s That Stench? Tips for seeking out nasty smells

  1. Isolate the odor;
  2. Search possible sources, such as ventilation, heating and air-conditioning ductwork;
  3. Ask residents about recently used appliances, such as the dishwasher, stove, microwave, self-cleaning oven, etc.;
  4. Check light fixtures for darkened bulbs and heat;
  5. Examine fuse/breaker boxes for heat;
  6. Check computers (and ancillary equipment) for functionality;
  7. Search trash receptacles for any discarded or burned food;
  8. Scan immediate outdoor area for decomposing mulch;
  9. Check in and around outdoor heating units for signs of skunks;
  10. Run water down any drainpipes to restore traps; and
  11. Use available resources such as a fresh, unclogged nose, heat guns, TICs and toolboxes.


  • Greg Jakubowski, a fire protection engineer and certified safety professional, started his fire service career in 1978. Currently, he serves as a Pennsylvania State Fire Instructor and as chief of the Lingohocken Fire Company in Bucks County, Pa. Jakubowski is also a member of the IAFC and a principal in Fire Planning Associates, a company dedicated to helping fire departments, municipalities and businesses with pre-emergency planning.

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