Some areas in repair garages are considered "classified areas", primarily because of the potential for fuel vapor buildup. Wiring in such areas is subject to very demanding requirements, including the use of rigid or IMC conduit, threaded connections, explosionproof boxes and fixtures, and proper sealing to prevent flammable vapors from moving through the conduit to remote locations.
The fittings shown here are called "sealoffs" or "EY seals", and are used to physically seal the conduit at the boundary of the hazardous area. After the wires are pulled, a liquid sealing compound is poured into the fitting (through the plugs with the square recesses), which fills up the spaces around the wires and prevents flammable vapors from passing the seal.
The use of EMT fittings could allow flames and hot gases from a vapor explosion inside the conduit system to ignite the surrounding atmosphere. Only threaded connections are allowed here.
The requirements for wiring in hazardous locations are spelled out in Articles 500 and 501 of the NEC.