A safety system may include a monitoring device that receives analog values of various parameters from one or more safety appliances. The analog values may be compared to upper and lower control limits in control charts for the parameters for each safety appliance. When an analog value falls outside of the upper control limit or lower control limit in the control chart, an alert may be issued to indicate that the safety appliance may be degrading or failing. The monitoring device may also generate control charts for safety appliances from the analog values output from the safety appliances.