They used off-the-shelf studio flashes. There really isn't a whole lot of "calibration" nor chance for "miscalibration".
The nature of these units prevents them from outputting a bright light for more than a few milliseconds. Any catastrophic failure would have most likely resulted in the flash bulbs exploding with sparks and flying glass shielded by the projection screen. Had that happened it would have only enhanced the effect.
Those flashes work by charging a capacitor bank to 1kV, then discharging it through the flash bulb. The components are selected to maximise the current during the discharge. In other words, they are designed to output as much power as possible. Any kind of failure can only reduce the power and/or energy from the intended.
The nature of these units prevents them from outputting a bright light for more than a few milliseconds. Any catastrophic failure would have most likely resulted in the flash bulbs exploding with sparks and flying glass shielded by the projection screen. Had that happened it would have only enhanced the effect.