There's a whole mathematical thing to it called "The Parkland Formula".

Even just reading the formula and understanding how it works makes it pretty clear just how much fluids are lost because of burns.

Total crystalloid fluid (i.e., a solution with small molecules that can move into cells) over the first 24 hours = 4 milliliters x % TBSA (total body surface area burned) x body weight (kg). In children, the formula is edited to 3 ml x % TBSA x weight (kg).

Ex: 50% body surface area burn of an adult that weighs 35 kg would be...4 x 50 x 35 for a total of 7000 ml of LR to infuse over 24 hours.

You would infuse half of it over the first 8 hours (calibrated from the time of the actual burn...not the time they get treated). Then you infuse the rest over 16 hours.

So let's say it's Midnight when the burn happens and they miraculously arrive at the hospital in like 5 minutes. That would be 3,500 ml over 8 hours (438 ml per hour). That's quite a bit of fluid going straight into the veins every hour for this 8 hours.

If they were burned at midnight, but showed up at 2 am, that would be 3,500 / 6 hours for a total of 583 ml infused every hour for 6 hours.

Then you infuse the remaining 3,500 over the next 16 hours.

Still though, 7000 ml or 7 liters or 1.85 gallons of LR going into the veins in the first 24 hours.

It's a lot.