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How to test for combustible gas or flue gas leaks: This document explains how to use the TIF 8800 combustible gas analyzer and similar equipment, outlining methods used to test for the level of toxic and other gases in buildings and in outdoors.
In related documents we give references and explanation regarding toxicity of several of the most common indoor gases, based on literature search and obtained from the U.S. government and expert sources. We include reference links to many articles that can help diagnose the source of dangerous carbon monoxide in buildings.
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Flue gas detectors and combustible gas analyzers such as the TIF8800 discussed here can add an additional level of testing for dangerous gas leaks, flue gas leaks, and assist in detecting leaky chimneys or unsafe gas or oil fired heat exchangers.
This text may assist readers in understanding these topics. However it should by no means be considered exhaustive.
We include safety warnings about relying on any instrument to detect flue gas leaks, natural gas leaks, LP or propane gas leaks, etc.
In our photo at left the TIF 8800 combustible gas analyzer is being used to check for flue gas spillage at the built-in draft hood intake at a gas furnace.
Watch out: Seek prompt advice from your doctor or health/safety experts if you have any reason to be concerned about exposure to toxic gases.
The photograph at left shows our TIF 8800 combustible gas analyzer being used to sniff for possible sewer gases at an industrial sink. Just about any building drain at a sink includes a local plumbing trap that will produce low levels of detectable gases.
[Click to enlarge any image]
The TIF 8800 gas detection instrument is very sensitive to a wide range of combustibles and hydrocarbons, and is a quick and reliable way to check for gas leaks at LP or natural gas lines as well as for flue gas spillage.
An audible signal which makes a "geiger-counter"-like ticking noise will speed up as the sensor is moved closer to a leak source. This permits the user to not only detect that a combustible gas leak is present, but to follow the gas leak concentration to its source.
The difficulty of making sense of sensitive gas test instrument readings is illustrated by our photographs just above. Called to track down "chemical odors" in a New York law office we found that all of the offices in a one story building shared a common ceiling plenum through which HVAC return air circulated.
At the opposite end of the building from the law office was a beauty parlor whose chemicals proved to be the odor source. Checking the sink (above left) where chemicals were used gave a strong reaction from our TIF8800, but the main chemical source proved to be a closet in which loosely-capped, leaky, and even spilled chemical bottles were stored (above right).
The user can adjust the actual field sensitivity of the instrument using a knob visible at the lower right of the silver control panel in the photograph. The TIF instrument company rates the instrument as responding to very small traces of combustible gases, from 50 PPM to 1000 PPM.
When checking gas piping for leaks, if the plumber has recently sealed a connection using certain pipe sealants containing aromatic hydrocarbon solvents, this instrument will respond just as if there were a gas leak.
It's a fabulous tool when used with thought, and it has often found gas leaks that were otherwise missed by the soap or match (dangerous) method used by many plumbers.
To maximize the sensitivity of the TIF8800 and thus its ability to detect combustible gas leaks, we recommend turning on the instrument while outside in fresh air (and away from any running automobiles or similar equipment).
Let the instrument stabilize, adjust it for a steady but fairly sensitive beeping tone, then enter the area to be inspected.
Following a warm up period (electrode in the sensing tip has to heat up) an adjustable dial sets a tic noise to a steady but modest rate. The manufacturer says to use a rapid rate - which is a more sensitive setting.
As the sensing tip is moved into test locations the operator listens for an increase in the tic rate. The faster the tic the higher the concentration of whatever is being detected.
Your breath will make the instrument respond, even if you're sober - because of its humidity. Gas leaks in any serious quantity will promptly change the tic rate to a continuous siren.
If the siren sounds before the leak source can be identified, the air in the area is contaminated with heavy concentrations of gas. The user can desensitize the tip by turning the control knob to a slower tic rate. When looking for small leaks, a high tic rate must be used.
When to make heating furnace plenum measurements for gas leakage
At CO DETECTION OPTIONS we expliain in detail that when using any gas detector tool to test inside of the air plenum of a fossil-fuel fired appliance as a screen for CO or flue gas leakage, a critical test time is before the blower fan has come on. That's because once the fan begins not only is building air in the plenum diluted, the pressurization of air around the heat exchanger may change the direction of a combustion gas leak.
When using the TIF 8800 or similar gas detectors, remember to test the air for combustible gases at various levels or heights
As we illustrate below, test building air at floor, mid-room height, and near the ceiling, since despite the varying weights of gases (such as LP gas and natural gas), a combustible gas or flue gas might be found at an unexpected location.
For example, flue gases that should be heavier than air and should be found accumulating at floor level may in fact be accumulating at ceiling level in a building where they are carried while mixed with other hot or warm combustion air products (which rise by natural convection).
Our sketches illustrate at least three test locations that should be checked when using a CO detector or a Combustible gas detector (like the TIF-8800)at a heating appliance.
We test at the appliance, we test at the floor (heavier-than-air gas mixes including LP gas), and we test near the ceiling (warm air such as leaky flue gas rises). You may find surprising results.
We inspected a property that had suffered an LP gas explosion and damage. An screened porch was enclosed by solid walls in its lower half. An LP tank stored there was attached to a portable barbecue unit and was leaking.
The property owner opened the kitchen door to access the screened porch whose lower half was filled with LP gas. When the kitchen door opened and a kitchen light switch was operated, LP gas that had entered the kitchen from the porch exploded.
Also see HEAT EXCHANGER LEAK ALLOWED - separate article
Because the TIF 8800 responds to a very wide range of combustible gases, it is useful in tracking down sewer gas or septic gas odors as well. See
Yes and No. If the instrument responds we don't know just which gas it is responding-to as it is very sensitive to a wide range of hazardous and combustible gases. However, as carbon monoxide released from a heating appliance such as a furnace, boiler, or water heater is being produced by gas (or possibly fuel oil, kerosene, coal or other bio fuel) it is not going to be produced in pure nor isolated form.
Rather the CO (carbon monoxide) will be mixed with leaking or spilling flue gases.
For this reason alone, in our OPINION the detection of abnormal flue gas spillage would be a sufficient indicator of unsafe conditions in a building regardless of the absolute level of carbon monoxide in the mix at that moment.
What the heck is "abnormal flue gas spillage?" Well it's normal for there to be a brief burp or spill of flue gases from many heating appliances at the time of burner start-up and before the chimney has become heated enough to establish full draft. Certainly after a few minutes (five minutes is a reasonable rule of thumb for most residential buildings) there should be no ongoing flue gas spillage at the appliance.
Safety Warnings About Using a Gas Detection Device to Check for Dangerous Flue Gases or Natural Gas / LP / Propane Gas Leaks
Our photo at left shows a dangerously leaky heating flue - in this case it was visually obvious and no flue gas detection equipment was necessary.
Watch out: when inspecting and testing furnace heat exchangers for leaks, don't forget to look for other flue gas or carbon monoxide leak sources such as shown in our photo at left. Failure to observe a gross safety hazard such as this one risks focusing on the wrong hazard.
False positive gas test results: The TIF8800, for example, is a wonderfully sensitive instrument and it can detect very low levels of flue gas or combustible gases.
But it will also respond to other substances that are miscible in air. Just try breathing on the sensing tip when the instrument is set to a sensitive position and you'll get a response. So test instruments work best in the hands of a very experienced building investigator and instrument user.
False negative results: any gas detection instrument is vulnerable to variations in building conditions or in the operation of mechanical systems in the building that can temporarily hide the presence of a dangerous gas leak. For example, a leaky heat exchanger in a heating furnace may leak detectable gases into the warm air plenum only until the blower fan comes on. Changes in building pressures, open or shut windows or doors, fans on or off, and other such variables can completely change the detectable presence of a dangerous gas indoors.
For this reason, if you call a fire department or emergency worker to test a building for the presence of a dangerous gas such as flue gases, leaks in natural or LP or propane gas lines or equipment, or carbon monoxide levels, even if the worker detects no gas leak present at the time of the inspection that is not a guarantee that the building is safe.
What should you do about this gas test reliability problem? Where there are reasons to be concerned about unsafe gas levels in a building, a more thorough building investigation is in order. Such an investigation includes at least
Readers should see GAS DETECTOR WARNINGS for additional recommendations.
Where to Buy the Tif 8800, 8800A, or 8850 Combustible Gas Analyzer or Where to Get Your Instrument Repaired
(Oct 9, 2011) Anonymous said: where to get it repaired?
Reply: Anon when my TIF instrument needed repairs I contacted TIF Instruments and then arranged to send it to them for repair work - the results were fine.
TIF instruments and other gas detection equipment are also sold by home inspection tool and equipment suppliers, plumbing and heating suppliers, and test equipment suppliers in most countries of the world. Examples include
Continue reading at TIF 8800 FIELD TEST or select a topic from the More Reading links shown below.
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Frequently Asked Questions (FAQs)
Question: how can I use the TIF 8800 to confirm a suspected gas leak when I smell gas?
I have this detector and it is giving a positive reading near a taped off sprinkler in the ceiling of a closet and also in my HVAC vents near the ceiling... my landlord says this is normal and that the meter is just overly sensitive, but I purchased this because I sometimes smell gas in this closet and sure enough the meter gives a positive as well. Any suggestions for how I should proceed when I'm being told that everything is fine even when I have a meter reading gas? - Anon. 1/24/2014
Anon: Thank you for an excellent question.
Also keep in mind that gases other than combustion fuel (LP or natural gas) can cause the instrument to respond. Examples include
Questions & answers and safety advice for using combustible gas detection equipment
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