According to the article "Sustainable Design for Plumbing Engineers", a good sustainable plumbing design will specify the installation of systems that minimize or eliminate the need for traditional construction methods that result in the off-gassing of odorous and potentially irritating Volatile Organic Compounds (VOCs). Which one of the processes below does NOT emit a "bad compound"?
1) welding joints
2) brazing joints
3) mechanical joints
4) gluing joints