The need for rigorous evaluations for objectively evaluating the program effectiveness of various health and safety and emergency preparedness and disaster response training is long established. In response to the Deepwater Horizon disaster, the National Institute of Environmental Health Sciences facilitated the presentation of health and safety training to over 147,000 workers (e.g., on-shore and off-shore volunteers, technical specialists) across the four Gulf States. The Gulf Oil Spill (GOS) health and safety training was designed to assist the workers in rapid and efficient mitigation of continued environmental contamination while ensuring minimal impact to public health. A comprehensive evaluation process was developed to assess effectiveness of the GOS health and safety training. This evaluation process was designed to gather and integrate quantitative and qualitative information regarding the workers' satisfaction with the training as well as knowledge acquisition and transfer of training to improved health and safety behaviors during the clean-up activities. Evaluation data was gathered from two distinct worker sub-populations from the Gulf States, that is Islenos and Vietnamese workers assisting in the environmental clean-up efforts. Significant and meaningful differences were found with respect to the training-related opinions, knowledge, skills, abilities and behaviors reported among the sub-populations. Results will be discussed vis-à-vis making quality improvements to the training, identifying best practices, and making better use of available resources and strategies. The application of this evaluation system and resulting evidence will be highlighted including implications for strengthening other worker health and safety programs in disaster response and guiding related policy development.