It is still seen that crews in the field are using hammers and crowbars while delivering several tons of force on equipment to separate flanges. The likelihood of injury to people and damage to piping, gauges and material from these various ad hoc methods are inevitable. There are many solutions out there to separate flanges. Here are a few to mention and select from.
Hammer, crowbar and other standard tools are still commonly used --> not recommended.
Accepted are portable manual flange spreaders that can work well.
The same principle but as a hydraulic version can be found in the industry and is applied where more force is required.
Overcoming fused flanges where conventional pulling capacity and space are limited, hydraulic jacks so thin they can be inserted between corroded flanges are available. Hydraulic jacks so tough they can be pressurized to exert hundreds of tons of force, causing the toughest of problem flanges to separate. --> Costly but recommended when flanges are heavily corroded and other methods won't work.
Another simple solution is a so-called "Flange Boy" which is one of the easiest solutions to separate flanges with thread sizes from A 3/4 - A 1 5/8 or D18 - D42. It allows you to apply heavy loads without risking damage to the support plate. Despite its long existence, some people might have still not seen this unique solution. --> Cost-efficient, easy, small and available in many bolt sizes --> Video