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Transite HVAC air ducts:
This article explains the potential hazards of transite (cement asbestos) air ducts - asbestos fiber release, radon, and indoor air quality concerns, and duct collapse when transite air ducts are is found in buildings. Transite pipe, an asbestos-cement product, was used for HVAC ducts and for chimney or flue material to vent gas-fired appliances.
Cement-asbestos transite pipe may also have been used for water piping in some communities.
We discuss how to identify cement asbestos transite air ducts, what the safety & health hazards are, how to seal or abandon the ductwork, & alternative approaches.
This document assists building buyers, owners or inspectors who need to identify asbestos materials (or probable-asbestos) in buildings by simple
Transite Pipe HVAC Ducts: Asbestos Heating or Air Conditioning Duct Material Warnings
Transite pipe, which contains significant percentage of asbestos fibers, was often used for heating ducts and on occasion heating
and cooling ducts in older buildings. Transite pipe used as HVAC ducts or air ducts for heating and air conditioning was often installed buried in a concrete floor slab - methods that placed
the asbestos-cement transite piping below or in a building floor slab.
Asbestos-containing transite pipe HVAC ducts were also used
in exposed areas such as shown in the crawl space photograph at the top of this page. And transite pipes were also used as flues or chimneys for some heating equipment, usually where gas fired heaters were installed.
Definition & Composition of Transite materials
While the term "transite" has been used to describe many asbestos-cement products (pipes, ducts), Transite™ is the trademarked name used by Johns-Manfille for asbestos-cement products that were manufactured by that company to its own specifications.
Those specifications varied by individual products but typically included a mixture of 15-25% chrysotile asbestos, 45-55% portland cement, and another 25-35% silica "flour" (that I read as finely-ground sand).
We emphasize that while Transite™ pipe materials, if they have not been painted nor exposed to the weather, usually will display a black stencil-stamp identifying the company and product, for example "JM-TRANSITE-FLUE", many other asbestos-cement products of similar formulation were produced by other companies including Celotex, CertainTeed, GAF, National Gypsum, and others. See ASBESTOS PRODUCING COMPANIES.
Transite air ducts in slabs often collect water, mold, pathogens. We provide photographs and descriptive text of asbestos insulation and other asbestos-containing products
to permit identification of definite, probable, or possible asbestos materials in buildings.
The photo (above-left) of a sewer line routed immediately below a transite asbestos in-slab floor heating duct was provided courtesy of reader Conrad.
While an expert lab test using polarized light microscopy may be needed to identify the specific type of
asbestos fiber, or to identify the presence of asbestos in air or dust or water samples, many asbestos-containing building products
not only are obvious and easy to recognize, but since there were not other look-alike products that were
not asbestos, a visual identification of this material can be virtually a certainty in many cases.
Readers should also see:
ASBESTOS DUCTS, HVAC - Guide to Identification of Asbestos Materials On or In Heating and Cooling Duct Work: carbon monoxide hazards of transite chimneys and vents
Transite-type HVAC or Air Duct Asbestos Warnings & Hazard Details
Transite ducts used for HVAC air flow, especially when used buried in building
concrete floors or slabs, may break, collapse, leak water in (forming a mold and bacterial reservoir in the HVAC system,
or may release asbestos and other particles in building air when the HVAC system is operating.
An up-flow or down flow furnace in a building with concrete slab and with perimeter duct work
raises some important health and cost questions:
The photograph above shows a transite cement asbestos heating duct in a carpeted floor slab.
We recommend that in-slab heating or air conditioning ducts made of transite be sealed and abandoned, and alternate heat sources installed. This improvement
removes an asbestos hazard, a flooded duct and mold hazard, and in some locales, also a radon gas entry point.
The photograph shows the edges as well as surface of the transite material. Transite pipe
HVAC ducts get quite dirty and are not always easy to identify. [Photo and comments on transite in-slab HVAC ducts
courtesy of Roger Hankey, a Minnesota home inspector.]
Asbestos hazards of transite ducts: Cementious duct material may contain asbestos. What is this "cement"
duct work made of Cement and asbestos fibers.
How much asbestos is in Transite pipe? While it's cementious, transite ducts or even transite pipe used
for heating flue vents is a potential asbestos hazard in buildings. Transite pipe typically contains about
15% to 25% asbestos fibers, typically fibrous chrysotile asbestos.
A careful asbestos testing lab may report both fibrous and fragmented
asbestos which can occur in still smaller pieces (thus more easily remaining airborne and increasing human exposure to asbestos).
The balance will be cement and possibly other fibers or binders. If transite pipe is damaged or is cut mechanically (such as by using power equipment), friable, airborne asbestos fibers may
be generated - a health and costly cleanup concern.
HVAC air ducts located inside concrete slab floors invite flooding, mold, insects, and where transite - cement asbestos - ductwork was used, asbestos particle contamination or collapsed ductwork.
SLAB DUCTWORK - catalogs the functional and environmental problems found when HVAC air ducts are routed in or below floor slabs
Air quality hazards of in-slab duct systems: include water leaks into the duct system which can in turn generate a
mold or bacterial hazard or can cause softening, collapse, and blockage of the in-slab transite pipe duct.
While there are companies offering duct cleaning and duct sealing services, we remain cautious
that such a "sealing" project creates a false sense of confidence that no remaining duct issues exist, causing the
occupants to miss the discovery of future leaks and in-duct problems.
Radon entry through in-slab duct systems: can occur in areas where radon is present at problem levels in the soils.
In particular, because a return air duct is often at negative pressure (when the blower is operating), the movement of radon
gas from the soil into the building air through a leaky in-slab duct can be significant, certainly greater than the movement
into the building from other openings such as through a basement slab crack.
Sewer Gas entry into the HVAC duct system through in-slab transite asbestos ductwork: as reader Conrad discovered while tracking down the odor of sewer gas that was appearing in a home's in-slab ductwork, placing in-slab ductsclose to sewer piping (or septic system piping ) invites any future sewer gases leaking out of the piping right into the HVAC duct system. SLAB DUCTWORK
The owner tracked the sewer gas odor that was coming out of the building's heating ducts to a break in the sewer piping located in the same floor.
The repair of the sewer gas odor involved jack-hammering out the floor slab, removing and replacing the leaky cast iron sewer pipe, and repairing the floor.
Because of the inconvenience and cost of relocating these air ducts or converting to an alternate heating distribution method, the owner elected to retain the transite in-slab floor ducts.
This case of cast iron drain leaking sewer gas into a transite asbestos heating air duct is illustrated in more detail at CAST IRON DRAIN PIPING.
Incorrect spellings of transite asbestos piping or transite duct material that we've seen include transit pipe, transit ducts,
transite chimneys, transide pipe, transide ducts, and transight pipe or transight ducts. "Transite" is the correct spelling.
Recommendations where Transite Asbestos HVAC Ducts are Installed
Apply an internal transite HVAC air duct sealant
There are also duct-sealants that some contractors offer as an in-duct sealant/spray. The contractor extends a spray wand into the HVAC ducts to deliver a coating that, if perfectly successful, can prevent or at least reduce the risk of asbestos fiber release into the building air.
And Andrew Oberta has described standards methods for repairing asbestos-cement products including underground transite piping.
A down-side with in-slab ductwork is the difficulty in accessing for application of the spray and difficulty in inspection in the future to see what's going on inside the duct: collapsing walls, sealant falling off of duct interior, flooding, mold, asbestos-releasing scraps, rodents, etc.
Our in-slab air duct photo (left) shows evidence of a history of floods in the duct system as well as rodents (the rodent poison).
A second concern is that even if the coated transite air duct interior surfaces appear to have been treated successfully, especially with in-slab ducts we are not assured that the in-slab ducts remain clean, dry, and undamaged in the future nor that the transite duct interior coating remains bonded to the duct surfaces.
See SLAB DUCTWORK
But given the history of concerns with the product, in particular with in-slab ducts, we would give strong consideration to abandoning in-slab ductwork entirely.
Abandon in-slab and other transite asbestos HVAC air ducts
We recommend abandoning in-slab HVAC air ducts, including transite asbestos cement HVAC ducts, reasoning that there are multiple indoor air quality and potential health as well as functional concerns with such installations.
We described concerns with ductwork run in floor slabs in the article above, including risks of air duct collapse that interferes with air flow through the system, water leaks into the in-slab duct system (not a problem unique to transite ducts), and rodent or insect infestations or even mold contamination.
At SLAB DUCTWORK we give details about abandoning in-slab HVAC ductwork. That article also catalogs the functional and environmental problems found when HVAC air ducts are routed in or below floor slabs.
When abandoned, in-slab ductwork of any material can usually be left in place. However where radon gas is an issue, we seal the ducts at the air delivery registers in the building floor slab, as well as sealing any slab cracks that may allow radon gas to enter the building at increased levels.
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can I seal a crack in a transite HVAC duct?
Can a crack in a transite HVAC "duct" be sealed or repaired. I am having foundation issues with my slab on grade living room and one of the ducts is cracked. - Brad 8/6/11
Brad transite is a cementious product. It could be "repaired" using a bonding agent and high-portland content patching cement, and perhaps even duct seal.
There are also duct-sealants that some contractors offer as an in-duct sealant/spray. A down-side with in-slab ductwork is the difficulty in accessing for application of the spray and difficulty in inspection in the future to see what's going on inside the duct: collapsing walls, sealant falling off of duct interior, flooding, mold, asbestos-releasing scraps, rodents, etc.
But given the history of concerns with the product, in particular with in-slab ducts, I'd give strong consideration to abandoning in-slab ductwork entirely.
Question: Water leaked into our transite air ducts - is this a problem?
I had some water get into my transite pipe buried into the slab of my house. I stopped the water by putting a new cement slab and redirecting the water. I immediately dried it up with a wet vac and kept the air conditioning on. I obviously have a leak in the pipe and have noticed some debris which I had removed by a HVAC vacuum company. I was told by an inspector when I bought the house that the transite probably had asbestos. Is this a problem? What should I do ? - Jack 9/22/12
Jack: I'm not sure which concern or problem you were asking about.
Basically if you abandon an in-slab transite pipe duct and seal the floor (you added another layer of concrete over your original floor slab) so that it can't easily send radon, rats, or mold into the building, it's not much of a concern - the cement-asbestos material won't move up through the new slab and thus won't be an ongoing asbestos hazard.
Your inspector, by saying that transite "probably had asbestos" was perhaps trying to please the seller and real estate agent from whom s/he receives referrals. Transite HVAC ducts are a cement-asbestos product and contain about 50% asbestos materials (fibers and powder filler) by volume.
Because it's in a cementious form the transite duct material is not normally friable so is less likely to release significant levels of asbestos into building air than softer asbestos materials such as asbestos pipe or boiler insulation. But when water-damaged or mechanically damaged, the asbestos release hazard from transite ducts can increase significantly.
What should a homeowner do about a transite air duct system? Is it a health hazard? I have two 12 - 15 foot lengths of HVAC ducts under a slab portion of my home. The ducts look to be in good shape through visual inspection from the floor vents with the exception of one crack (see post and answer below). If I want to stop using the ducts, what should I do as far as sealing them off from the furnace? I have installed a gas burning insert in the room so I can get away without using the ducts. Any help would be greatly appreciated. - Brad 6/11/12
If you abandon use of a transite duct, and provided it's not damaged so as to have become friable (releasing dust, easily crumbled between your fingers) it can be left in place - it's not "radioactive" - and is better left undisturbed. Don't run power tools, saws, grinders, etc. on cement asbestos material. But in the article above we give some reasons why in-slab air ducts of any sort present indoor air quality risks and hazards from future and un-discovered flooding, rodents, mold, etc. Add to that the risk of softening (asbestos fiber release) from water or moisture condensation in the ductwork, and the collapse risk. I'd prefer to abandon the in-slab ducts (SLAB DUCTWORK) and seal off those supply registers.
With that approach, and as long as there are not other slab cracks that leak contaminants into the building, it may not be necessary to try fill the entire in-slab duct with cement or other fillers, and the material can safely be left in place.
(Apr 3, 2014) Anonymous said:
About transite air ducts, and asbestos cement air duct issues: Was there a time frame these asbestos cement ducts were installed, or are they still being installed today?
Transite asbestos HVAC ducts are not currently installed in any country that I know about, nor is the material used for new water pipes, chimneys etc. The time frame for cessation varies by country, generally late 1970's to early 80's.
(July 13, 2014) Anonymous said:
Where transite ductwork is found to contain asbestos, should the furnace also be replaced/
No, there is no justification for furnace replacement on that basis. But cleaning may be appropriate.
To be clear about the wording of your query, transite duct is not "found to contain asbestos" - it does contain asbestos.
Is it justified to replace the furnace because there was asbestos dust contamination in the ductwork?
It's likely that there has been some airborne asbestos through the duct system and the air handler, though just how much depends on a number of variables including the amount of damgaged asbestos, moisture levels (water in in-slab ducts may have reduced the hazard though produced a different mold issue), air velocity, other dust levels, and surly other variables.
Unfortunately, when I've run into this sort of issue (which I've seen a few times) the cost estimate from the cleaning company to properly and thoroughly clean the equipment is greater than the replacement cost.
Your options are to inspect, identify the highest risk locations and test dust and debris from those areas for asbestos, acting accordingly on the results, (probably spending a few hundred dollars on testing), or to just replace the equipment.
If the furnace is more than 20 years old I'd lean towards replacement of furnace, ducts, and other parts that are not easily cleaned.
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Questions & answers or comments about transite air ducts: asbestos cement air duct issues.
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 Thanks to astute reader Conrad for discussion of the procedure for diagnosing and curing the cause of sewer gas odors in ductwork, 01/31/2010.
 Asbestos Identification, Walter C.McCrone, McCrone Research Institute, Chicago, IL.1987 ISBN 0-904962-11-3. Dr. McCrone literally "wrote the book" on asbestos identification procedures which formed
the basis for current work by asbestos identification laboratories.
 Stanton, .F., et al., National Bureau of Standards Special Publication 506: 143-151
 Andrew F. Oberta, "A New Standard for Repair and Maintenance of Installed
Asbestos-Cement Materials", web search 6/11/12, original source: http://www.worldasbestosreport.org/conferences/gac/gac2004/pl_6_06_e.pdf [copy on file as Asbestos_Cement_Repair_Oberta.pdf], Andrew F. Oberta, MPH, CIH
The Environmental Consultancy
The ASTM Standard Practice for Maintenance, Renovation and Repair of Installed Asbestos
Cement Products has been developed by ASTM International
and assigned the designation E2394.
The standard provides the underlying rationale and detailed procedures for working with asbestos cement products – roofing, siding, ducts, pipes and other construction materials – that have already
been installed in and between buildings. It covers operations that can produce dust and airborne
asbestos fibers – drilling, cutting, breaking, filing, etc. – during routine maintenance, repairs and
small-scale renovation. Control of dust and fiber release using wet methods – soapy water, shaving
cream and similar substances – is stressed. Four appendices cover underground pipes, buried
ducts, drilling holes and removing panels, and additional appendices will be prepared to cover
other operations and materials. Installation of new asbestos-cement products is not encouraged by
the standard. Large-scale abatement is not the intended purpose, although some of the procedures
may apply to such operations.
The procedures are intended for use in developing as well as industrialized countries; therefore, the
use of hand tools and easily-obtained equipment and supplies is emphasized. The use of power tools
is discouraged to minimize the possibility of creating airborne fiber levels that would require
wearing respiratory protection.
E2394 is intended for use by supervisors and managers responsible for construction and
maintenance as well as by government agencies and NGOs responsible for worker and community
health programs. The standard offers useful guidance for countries in the process of developing
their asbestos laws and regulations. ASTM International intends to provide training on the use of
this standard in countries where it will be used through arrangements with standards organizations
in those countries.
 Anavi Z, Dizenhouse D, Oberta AF. Remediation of Land in Israel Contaminated by Asbestos Cement
Waste Material. Global Asbestos Congress, Osasco, Brazil. September 2000
 Brown SK. Physical Properties of Asbestos-Cement Roof Sheeting after Long-term Exposure. J. Occup.
Health Safety-AustNZ 1998, 14(2), 129-134.
 Asbestos: Publication of Identifying Information; Notice. U S Environmental Protection Agency,
Washington, DC. Federal Register, February 13, 1990.
 ASTM E2394, ASTM Standard Practice for Maintenance, Renovation and Repair of Installed Asbestos
Cement Products, available from ASTM International, www.astm.org.
 ASTM E1368, ASTM Standard Practice for Visual Inspection of Asbestos Abatement Projects
 ASTM E2356, ASTM Standard Practice for Comprehensive Building Asbestos Surveys
 Nguyen, Tuan ; Hamilton, Jill, " Asbestos in Crawl Spaces", Corporate author: Naval Facilities Engineering Service Center, Port Hueneme CA, Oct. 1999, web search 6/11/12, PDF source: http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA370467, Abstract : This document has been developed for use by Navy Asbestos Program Managers (APM), industrial hygenists, Safety and Health Managers, and facility managers to address asbestos contamination in crawl spaces. The contents provide direction for managing and abating asbestos hazards in these areas. Section 1 contains primarily the technical and regulatory requirements. Sections 2 and 3 are checklists with detailed discussions for clean-up or abatement in crawl spaces. These augment the NFESC Field Procedure Manuals for Managing Asbestos Abatement Demolition and Renovation Contracts, TM-2210-ENV and TM-2211-ENV, respectively. Section 4 lists the regulatory and technical references.
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