The most appropriate action when a tolerance threshold is exceeded is to communicate the potential impact to the decision makers. A tolerance threshold is the acceptable level of variation or deviation from the expected or planned performance or outcome of a risk response. When a tolerance threshold is exceeded, it means that the risk response is not effective or efficient enough to reduce the risk to an acceptable level, and that the enterprise is exposed to unacceptable levels of risk that could impair its ability to achieve its objectives. Therefore, the potential impact of the risk should be communicated to the decision makers, such as senior management, risk owners, or risk committee, who have the authority and responsibility to decide on the appropriate actions to address the risk situation. Communicating the potential impact can help to raise the awareness and urgency of the risk issue, and to facilitate the risk-based decision making process. Researching the root cause of similar incidents, verifying the response plan isadequate, and increasing human resources to respond in the interim are not as appropriate as communicating the potential impact, as they do not address the primary need of informing and involving the decision makers, and may not be feasible or effective in resolving the risk issue. References = CRISC Review Manual, 6th Edition, ISACA, 2015, page 41.