Perkins Engines, Honda, Nissan, and Ford all use fixed systems to monitor for flammable gases and carbon monoxide in their engine test laboratories.  In these places they run engines in a small room to test their performance, and there is the possibility of fuel leaks and toxic gas build up.

Nissan also have systems for monitoring oxygen and carbon monoxide on the production line in the pits, simply for personnel safety.  SI-100 series are good for this.

Safety engineers, plant managers and test engineers are good first contacts for these applications.