100psi in a 38mm tire puts roughly the same stress on a rim flanges as 150psi in 25mm tire. This is well within the rim's strength when new, but can become borderline when the rim is worn down to the indicator dots.

BTW- my commuter has 2" tires and I routinely inflate to 60psi in the rear, letting them bleed back to 50 over the week. This is comparable rim stress to a 38mm at 80psi, or a 25mm at 120. My rims are well worn, and probably at or near the wear limit (old rims without an indicator), so sometime within the next few months, I'll post what the remaining wall thickness was when they cracked.