This article was updated in July 2026 to reflect current EPA Method 204 guidance.
Fugitive VOC emissions are the uncontrolled release of gases to the atmosphere — vapors that never make it into a control device at all. A well-built thermal oxidizer, RTO, or catalytic oxidizer routinely destroys 95–99%+ of the VOCs that reach it, but that destruction rate only counts toward your permit if the emissions actually get there.
Overall control efficiency is: Overall Control (%) = Capture Efficiency (%) × Destruction Efficiency (%) ÷ 100
If your capture system is only 70% effective and your oxidizer destroys 98% of what reaches it, your overall compliance number is 68.6% — often not enough to satisfy a permit limit. This is why fugitive emissions are frequently the single largest source of uncontrolled VOCs at a facility, and why regulators require a documented, tested capture strategy before crediting your oxidizer's destruction rate at all.
