Yes, you should be cautious, but you don’t need to avoid every metal street bench. During a heatwave, direct sun can heat a metal seat well above air temperature. Dark-colored, solid steel or aluminum benches can become painful to touch, and prolonged contact with bare skin may cause a burn. It’s not that metal always “holds” heat better than everything else; it conducts heat very efficiently, so it transfers that heat to your skin fast.
A quick test helps. Hold your hand an inch above the surface. If it feels like a radiator, don’t sit. If you must sit, tap it quickly with the back of your hand for a few seconds. If that’s uncomfortable, use a towel, jacket, newspaper, or find shade. Be extra careful with children, older adults, pets, and anyone with reduced sensation. Thin shorts or skirts offer little insulation.
Perforated metal, slatted designs, and light-colored coatings are usually safer because they shed heat and reflect more sunlight. If the bench is shaded or the sky has been cloudy, the risk drops a lot. Metal also cools fairly quickly once the sun is off it, unless the air itself stays very hot. So yes, respect hot urban furniture during a heatwave, but a little awareness and a quick touch test go a long way.