https://archive.is/JUevh

(Long may it live)

As to the grout accelerant in question:

TDS [PDF]: https://assets.ctfassets.net/ctspkgm1yw3s/DMSY-1685695220-39...

MSDS [PDF]: https://assets.ctfassets.net/ctspkgm1yw3s/3Tp3imoxG5XfZlrlzU...

I am not skilled in the arts of aggregate curing and occupational exposure, but I wonder if it’s the “silicic acid” or a non-table-variety of “sodium salt” (from the MSDS) that’s sloughing the firefighters’ skin off here… or something that happens when the sodium oxide (from the TDS) hits water? Chemistry class was a lifetime ago but does that turn it back into lye? Is the oxide technically a “sodium salt”?

Looking at the CAS number[1], it's the sodium oxide component of it that's likely the problem, yeah.

And yep, Na2O + H20 -> 2 NaOH, sodium hydroxide :)

[1] https://www.epa.govt.nz/database-search/chemical-classificat...