Abstract <p>The great advantage of steel structures in manufacturing and operation is their strength, reliability, taking into account the principles of unification and standardization, and short terms of installation. These characteristics determine the cost-effectiveness of using steel structures in construction. However, steel structures have such disadvantages as susceptibility to corrosion, as well as low fire resistance, slightly more than 400°C. The use of environmentally friendly fire retardant for metal “Thermobarrier” is considered as one of the ways to increase the fire resistance of metal-wood structures. The test method for the initial impregnation is described. Test result was the justification for the use of this impregnation to increase the fire resistance of metal-wood structures.</p>