We have optimized a procedure for igniting hydrogen-filled balloons containing metal salts to obtain the brightest possible flash while minimizing the quantity of airborne combustion products. We report air quality measurements in a lecture hall immediately after the demonstration. While we recommend that this demonstration be done outdoors or in a hood, the results show that contaminants do not exceed maximum allowable concentrations in a well-ventilated, large lecture hall. (Contains 6 notes and 3 tables.)