Tire Off-gassing & Earthships
Last week, as you know, I had the privilage of attending the presentations of the Permaculture Teacher training. One presentation in particular pricked my ears- that of Jeff Leinaweaver, who chose to talk about the use of old tires in permacutlure. I loved what he was saying, about the millions of uses of these giant toxic donuts could have instead of being thrown into the landfills or burned.
But of course, as with most permaculture conversations around ‘the problem being the solution’ the question was raised about whether it is a good idea to use tires in our gardens or natural buildings. We all know that tires stink and I’m sure you have been in more than one heated debate about Earthships or terracing that had to do with offgassing or leaching.
Well, today I found a tweet that led me to the Earthship Website where they proudly displayed some actual research on the topic!. Here is a little excerpt to quell your Earthship concerns with the contact info of the study locatedhere.
The following is an e-mail from an engineer in Alamosa, CO. As an engineer, I feel the need to respond personally to the technical content of the recent letter printed by the Toronto Star. This letter raises several concerns which in my judgment are not technically valid. I would like to preface my comments by stating that I am NOT an Earthship enthusiast, Earthship owner, and am in no way affiliated with Solar Survival Architecture. I AM an engineer with training and experience in dealing with these issues who finds the Earthship concept to be an interesting and novel approach to sustainable living.
What is “carbon black”? The following description of “carbon black” is found in Appendix A of the National Institute for Occupational Safety and Health (NIOSH) “Pocket Guide to Chemical Hazards”: NIOSH considers “Carbon Black” to be the material consisting of more than 80% elemental carbon in the form of near-spherical colloidal particles and coalesced particle aggregates of colloidal size that is obtained by the partial combustion or thermal decomposition of hydrocarbons. NIOSH also classifies carbon black as a class A (known) carcinogen. However, to assess the risks to human health and environment posed by the use of recycled tires in Earthships, one must look at the pathways of exposure, and the state in which this potential contaminant exists. The letter states that, “A tire under proper conditions will break down into the above products.” “The proper conditions” for rubber to degrade would be: high temperature, exposure to light, or the presence of strong oxidizing chemicals. None of these conditions exist when a tire is entombed in an Earthship wall surrounded by packed earth, vapor barrier, stucco, and paint. The argument has been made that tires must off-gas because “old tires smell.” The reason “old tires smell” is due to the photo degradation of rubber. Essentially what happens is that photons from light bombard the rubber and knock atoms from the long rubber polymer molecules. This causes the rubber to degrade, and smaller molecules to vaporize. In the absence of light, this does not happen.
Tires are not exposed to light when used in an Earthship. In order for the tires to affect the indoor air quality of an Earthship, the tires must off-gas vapors which must travel from the tires, through the walls, into the living space of the Earthship. The production of such vapors will be proportional to the vapor pressure of the compounds producing the vapors. The NIOSH pocket guide lists the vapor pressure of carbon black as “0 mm (approx.).” This is an extremely low vapor pressure. In other words, this chemical produces almost no vapor. What this means is that the potential for tires to affect indoor air quality will be severely limited by the extremely low vapor pressure of the source chemical. … more