Dewey and Laman are in error on this particular issue because they have not witnessed it first hand .
The science that makes this work is the fact that the OSB square that is on top of the fire is parallel to the ground and reflects the heat back into the fire and gets the wet wood burning hot enough to eliminate the smoke .
A 2x12 would work as good but is not readily available anymore because those 2x12 joist sizes have been mostly replaced by I-Joists in actual construction .
Neither Dewey nor Laman has witnessed first hand the science that makes this Top Panel reflectivity that stops the smoky fire .
If they had they would not have taken their position .
If you want to have a non-smoky fire from now on , try the reflected OSB panel on top of a smoky fire once .
One piece proves the remedy suggested to be effective .
After that you can make your own determination .
As to toxic , these fellows do not understand that the higher heat of the fire works to lower the emissions not unlike the catalytic principle in autos .
This is a case where actual campers building actual fires with practical experience have better insight to the solution .