Zelenka manufactures fire and smoke protection closures — timber, steel and aluminium fire doors and fixed or self-closing fire-resistant glazing to EI30 and EI90 — at its own works in Hennigsdorf, and installs firestopping and intumescent steel fire protection from its Berlin branch. Production is subject to Fremdüberwachung at least twice a year by the Überwachungsgemeinschaft Feuerschutz Berlin-Brandenburg and by ift Rosenheim, on the basis of DIBt approvals, and it holds ift Rosenheim certificates of constancy of performance for the Schüco and WICONA systems it fabricates. It carries out around six hundred fire protection maintenance jobs a year.