UPDATE 1, July 3, 2010 -- The tire regulation has been postponed, it is not in effect as of July 1st. There are problems with the wording that require ARB to re-draft the language. -- end update.
Original post begins:
There are numerous problems with the AB 32 tire inflation measure, soon to be law in California. The law goes into effect July 1, 2010. As a result of this ill-considered law, many vehicles will have tire-related accidents, and many lawsuits will be filed. Victims will need an attorney such as Roger Sowell who understands this law, and the issues surrounding tire inflation. The tire inflation law seems simple enough, but there are several problems.
Tires have a target inflation pressure written on the sidewall. Even if the service technician inflates the tire to the pressure from the sidewall, many things can make that the wrong pressure just a few hours later. The wrong pressure can lead to tire failure, causing injury, property damage, and / or death. Two of the things that can go wrong are discussed below.
First, the tire may be hot when the technician adjusts the pressure. A hot tire will have an elevated pressure, if it was properly inflated earlier when the tire was cold. Tires become warm or hot when driven at high speed for an hour or so. The air in the tire also becomes hot. Tires are designed to perform properly at the elevated temperature and pressure, if properly inflated when cold. If the tire is hot when the technician checks the pressure, he may let out some air to bring the pressure down to what is written on the sidewall. Later, when the tire cools down, the pressure will decrease and the tire will be underinflated. The hot tire problem is complicated because it is very difficult to measure the air temperature in a tire. If one could measure the air temperature, a simple correction table can be used to inflate the tire to the correct amount so that when the tire cools down, the pressure will be as written on the sidewall.
For example, if a tire is to be inflated to 32 psi when the tire is cold, or at 70 degrees F, the tire should be inflated to approximately 35 psi if the air temperature in the tire is 100 degrees F.
Second, the compressed air used to inflate the tire may be hot. Hot air flowing into a tire will eventually cool down, and the tire pressure will decrease. Air compressors heat up the compressed air as they run, and the air may remain hot in the storage tank. An air compressor usually has a storage tank, and the smaller the tank, the greater the chance that the air will be hot. This is especially true if the compressed air is used frequently. Only when the air compressor stops running for an hour or two will the air tank cool down. However, the opposite can happen when the air tank has been sitting overnight in the cold ambient air. If the air tank is cool and is at a high pressure, perhaps 80 to 100 pounds per square inch (psi), any air placed into a tire will be much colder due to expansion across a valve. Air auto-refrigerates when it is expanded across a valve. This is known as the Joule-Thomson effect. One can sometimes see this if one blows a small amount of air from the compressed air hose on a humid day. The cold air condenses the water vapor in the air, forming a small fog cloud that dissipates rapidly. If very cold air from auto-refrigeration is placed in the tire and the tire is inflated to proper pressure, the tire pressure will increase when the cold air warms up. Over-inflated tires can be dangerous, can rupture, and can cause accidents.
The legal liability that will result from the California tire inflation law should give all automotive service providers pause. With the record-keeping requirement, an attorney for a plaintiff who has a tire-related auto accident will turn first to the service provider that most recently adjusted their tire pressure. There is no practical and safe way the tire service company can properly inflate the tires, without letting the tires cool down to 70 degrees F, using 70 degree air from a compressor station, and double-checking that the tire gauge is properly calibrated and used properly. Tires do not cool down quickly; they take hours to cool down. The AB 32 tire inflation lawsuits are just waiting to be filed.
Roger E. Sowell, Esq.
Mr. Sowell can be contacted at his legal website.