Siebnen ventilation supplier holding two live VKF recognitions — 24743 in Untergruppe 502 Lüftungsschläuche and 27632 in 505 Absperrvorrichtungen. Untergruppe 505 covers the shut-off devices that close a ventilation path in the fire case where a full damper is not used, a family with only 22 approvals in the whole register.