Hydrogen release and combustion during severe accident scenarios can impose considerable loads on the containment structure and internal components. Either random sources (electric equipment) or spark igniters installed in the numerous containment rooms may initiate more or less accelerated deflagrations. To avoid damaging consequences, different concepts are available, which range from diluting or making the containment atmosphere inert to the use of igniters and catalytic recombiners. Spark igniters are used to burn the atmospheric hydrogen deliberately as early as possible, which means whenever it becomes flammable. A hydrogen deflagration model has been developed that is meant to estimate the combustion phenomena on a mechanistic basis as part of an integrated containment code to calculate severe accident sequences in the containment. It provides temperature and pressure loads resulting from deflagrations. The deflagration model is verified by applying it to specially designed deflagration experiments that can describe the type of premixed combustion to be found in nuclear power plant containments. The results demonstrate the potential of the model to describe the dynamics of a deflagration quite well. Due to deficiencies in understanding the nature of flame front growth, appropriate burning area stretching functions are derived from available experiments.