By the way, from what I can deduce thus far, the Permissible Cat is likely a combination of the MSHA-approved Terra Cat (ESWW's M Cat DOC and FST's fiberglass filter) and the reduced surface temperature design technology that we saw in the military (IR Shield) work.
Also, here is the CFR relevant to surface temperature control, which I found interesting. Note that ESW indicated in October their target temperature limit was 300 degrees F, while the CFR beloe notes 400 degree limit. It is nice to see we can undercut the allowed temperature by so much.
§ 36.48 Tests of surface temperature of engine and components of the cooling system.
(a) The surface temperatures of the engine, exhaust cooling system, and other components subject to heating by engine operation shall be determined with the engine operated as prescribed by MSHA. All parts of the engine, cooling system, and other components shall have reached their respective equilibrium temperatures. The exhaust cooling system shall be operated, but air shall not be circulated over the engine or components. Surface temperatures shall be measured at various places prescribed by MSHA to determine where maximum temperatures develop.
(b) The temperature of any surface shall not exceed 400 °F.
Note to §36.48: The engine may be operated under test conditions prescribed by MSHA while completely surrounded by a flammable mixture. MSHA reserves the right to apply combustible materials to any surface for test. Operation under such conditions shall not ignite the flammable mixture.
[Sched. 31, 26 FR 645, Jan. 24, 1961, as amended at 61 FR 55526, Oct. 25, 1996]
