Alarms are important for safe and reliable operation in process industries. Periodic alarm assessment is a crucial step in alarm management lifecycle that provides valuable feedback for fine tuning the alarm system. In this perspective tutorial, alarm data is represented using binary sequences and subsequently, two novel alarm data visualization tools are presented: (1) The High Density Alarm Plot (HDAP) charts top alarms over a given time period and (2) Alarm Similarity Color Map (ASCM) highlights related and redundant alarms in a convenient manner. The proposed graphical tools are instrumental in performance assessment of industrial alarm systems in terms of effectively identifying nuisance alarms such as chattering and related alarms based on routinely collected alarm event data. The special features and advantages of the proposed graphical tools are illustrated by successful application to two large scale industrial case studies, each involving over half a million observations for top fifty alarm tags. (c) 2012 Elsevier Ltd. All rights reserved.