vent pipe in return

I found this plumbing vent pipe running through the cold air return. Talked to a plumber and he said it was acceptable. An HVAC tech told me it wrong. Any thoughts on how to write it

Agree with the HVAC tech… it’s wrong. Even if allowed by the AHJ, it is still a potential health hazard.

In my best Arte Johnson voice: Very interesting.

For your review.

Note: 25/50 refers to flamespread/smoke rating for burning materials from ASTM-E84

Can insulated plastic piping meet the 25/50 requirement?

Plastic Piping in Return Air Plenums by R. C. Wilging - PE

Summary:Because plastic materials do not qualify as non-combustibles their use in air handling plenums has been an issue for years. The code provisions that cover this subject clearly refer to “exposed” materials. Questions about whether insulated plastic piping would meet the 25/50 limits have now been answered in the affirmative by ASTM E 84 tests of 4" and 6" PVC and ABS pipe with solid wall and with cellular core wall.

Introduction: Over the 26 years that I worked in the plastic piping industry, I received many calls pertaining to this subject. Usually the conversation started with a question that included the terms plastic piping and 25 / 50. From these references I could rather quickly bring the issue into focus by asking the following questions - Are you dealing with plastic piping in plenums ? Are you dealing with PVC sanitary waste / vent piping and roof drains ?

Most often the responses were in the affirmative. I had to tell the questioner that these code requirements derive from ASTM E 84, Standard Test Method for Surface Burning Characteristics of Building Materials, and that PVC piping will meet the 25 Flame Spread requirement but it will not meet the 50 Smoke Developed requirement. From that point the conversations usually went to another question: What can be done to meet these 25 / 50 requirements ?

Possible solutions - For years I responded to this question by reporting that since the Code reference is to the use of "exposed materials " and the 25 / 50 requirements limit what can be “exposed” in the plenum there appear to be at least two solutions that a code official could approve: 1) Box out the piping with framing and gypsum wall board in order to exclude it from the plenum, or 2) Cover the piping with insulation that meets the 25 / 50 requirements and will protect the piping from a fire if one should occur.

ASTM E 84 - This test method evolved from some tunnel test work done by Dr. Steiner at UL. Therefore, we still hear references to " tunnel test " and Steiner tunnel test. The test continues to be used as a primary reference in building and mechanical codes. Over the years some changes in terminology have been introduced so that many codes refer to the Flame Spread Index (FSI)and the Smoke Developed Index(SDI) to indicate that the numbers used are index values that carry no units. In addition, some modified smoke measurement methods have been developed that use the terms "peak and average optical density ". These are being used with the same tunnel and fuel provisions in tests that parallel ASTM E 84 (see UL 910 and UL 1887). In these two UL tests the " 50 SDI " value is replaced by “0.50 - peak optical density / 0.15 - average optical density.” These are being referenced in some of the code provisions for the specific products covered by these UL Standards. A recently published article ( ref 1 ) deals in depth with the subject of surface spread of flame and suggests some alternate test methods that have been developed and have certain advantages. However, they focus on testing materials used as wall or ceiling coverings within rooms. These alternate tests seem to be mostly tests on smaller specimens of materials. They do not address products such as piping, cables, or wiring as they are used in plenums.

As an interesting aside, the ASTM E 84 FSI / SDI requirement was even introduced into a NFPA Standard for sewer pipe to be used in sewage treatment plants. As a result, a concrete pipe trade association had a series of E 84 tests conducted on concrete pipe, corrugated steel pipe with asphalt lining, corrugated steel pipe with polymer lining, corrugated aluminum pipe, ribbed PVC sewer pipe, PVC sewer pipe, ABS composite pipe, and corrugated PE pipe. The techniques used to fit samples into the tunnel were interesting. The test results that were reported are shown in Attachment D-1

Test data available - My first encounter with actual ASTM E 84 testing was through a series of tests at SwRI in San Antonio in 1969. At that time we had E 84 tests run on 4" schedule 40 pipe samples made of 4 different PVC pipe materials. In doing those tests the specimen mounting issue was resolved by cutting the pipes in half lengthwise and mounting both halves on the AC board that was used as a ceiling of the tunnel. Two inch chicken wire was used to hold the 2 pieces in place. The results of those tests showed that all samples had FSI values of 10 or 20 but the SDI values were far in excess of 50. Attachment D-2 shows the sample mounting used in these tests and this resulted in about 26 + inches of pipe inner and outer surface being exposed to the flame even though the tunnel is only 17.25 inches wide.

In another series of E 84 tests on CPVC materials that were run to see how well the FSI / SDI values would correlate if pipe and sheet samples having the same mass per foot of length were tested, the results showed that the pipe sample yielded slightly lower SDI values.

In yet another series of tests, it was found that water filled pipes yielded lower SDI values than empty pipes. In all these tests the pipe ends were closed. Some of the tests were done with water flowing through the pipe sample at a very low rate but most were done without flowing water. This was an interesting investigation because some people expressed concern beforehand that the pipe might explode or that the tunnel might be flooded. Actually, there was no explosion and very little water leaked from the pipes during these tests. Most of the water remained in the pipe samples and the water was hot when the pipe was removed from the tunnel after the test. During the tests small amounts of water were released at the support rods nearest the burner.

Some water filled / empty pipe tests were repeated at another facility with a 48 long 1/2" deep stainless steel tray placed under the water filled specimen near the burner to catch any water that leaked out during the test. Subsequent tests were run without the tray after it became apparent that water leakage was minimal. Finally, tests on 2" and 3" CPVC pipe samples were conducted with preformed pipe insulation on the pipe sample. The intent was to determine to what degree the insulation protected the pipe from the flame. As these tests progressed it became apparent that the smoke being generated was from the insulation so the fire exposure was extended to 20 minutes instead of terminating at the E 84 prescribed time of 10 minutes. In both tests the values after the 20 minute period were below the 25 / 50 limits, and the pipe samples were scorched but not burned at the flame end.

Wisconsin Mechanical Code - The following is an excerpt from the current issue of this Code - - ILHR 64.41 Plenums “8 ) Plumbing: Plumbing within the plenum shall be of noncombustible material. (a) Exception: Plastic pipe and fittings may be used provided the plastic material is of the self-extinguishing type with an average extent of burn not greater than 10mm and an average time of burn not greater than 20 seconds when tested according to ASTM D-635. The plastic material shall be wrapped with at least one inch of noncombustible insulation or enclosed with 1/2 inch type X gypsum wallboard.”

This provision indicates either of the two “solutions” described above will meet these code requirements. I tried to determine when this provision was added to the code and what supporting data was used as a basis for the provision. It was reported that it has been in place for several years but the department was unable to find the supporting information files because files were lost or misplaced as a result of an of office relocation. One official indicated this section of the code was revised in 1986. It is likely this provision was introduced at that time. It was in the code before the most recent (1994) revision. State officials indicate this provision is now noted on many of the plans they review. A mechanical contractor reported that the use of insulated PVC piping in a library project reduced costs by 28% with a savings of $ 7000.00. The contractor also confirmed that such installations are quite numerous. He believes this code provision has been in effect for about 10 years.

Recent E84 Tests On August 25 and 26, 1999 Southwest Research Institute ran eleven ASTM E84 tests on various types of plastic DWV pipe. ASTM E84, sometimes called the “Steiner tunnel test,” is entitled, Standard Test Method for Surface Burning Characteristics of Building Materials. I was retained by the Plastic Pipe and Fittings Association to manage the project (See the table-E84 Test Results).

The purpose of these tests was to verify that plastic pipe shielded by 1 inch thick preformed pipe insulation can meet the building code FSI/SDI limits required for materials exposed in return air plenums. These requirements are a Flame Spread Index (FSI) of 25 or less and a Smoke Developed Index (SDI) of 50 or less based on the use of an ASTM E84 Test Method. These requirements are typically referred to as “25/50 results” in an E84 test.

Ten samples of the plastic pipe (both ABS and PVC) passed with flame spread results ranging from 0.00 to 4.8 (maximum allowable is 25) and smoke developed ratings ranging from 17.2 to 25 (maximum allowable is 50). One sample, a 4" cellular core ABS specimen did not pass by a very narrow margin (53 to 50). The test was successfully repeated. The retest showed quite satisfactory results of 0.3 and 24.9. Two samples, 4" and 6" solid wall PVC, were subjected to a longer (20 minute) test where optical density is measured as a test criteria. Both passed this test as well.

Summary - This issue has been around ever since plastic piping became a viable and cost effective alternative for use in these systems. The “possible solutions” I have offered are a common sense approach and in conjunction with the smoke detection requirements for plenums provide for life safety of the building. occupants. There was a recent code change proposal by a code official to bring this issue to closure but it was unsuccessful because the insulation thickness was not listed and test data was not supplied. The recently completed SwRI tests answer these questions. Thus, we believe this issue can now be brought to a conclusion. Therefore, a code change proposal has been submitted to the International Mechanical Code.