# Twitter-Based Safety Confirmation System for Disaster Situations
## 1 Introduction  
Recently, social media have played an important information-sharing role during disaster and crisis events [1; 2; 3]. In particular, the social media application Twitter has gained traction in disaster situations [4; 5; 6; 7; 8; 9; 10; 11; 12]. On Twitter, users can post pictures and short messages (tweets) in 280 characters (140 Japanese characters) or less. Among the most important features of Twitter is the ease of distributing information from posters to followers. Many Twitter users posted tweets of disaster-related information during major emergency events such as the Haiti earthquake, severe hurricanes (Sandy, Harvey, Irma, and Maria), the Boston Marathon bombing, and typhoon Haiyan [7; 8; 9; 10; 11]. Many of these active tweets included hashtags of the disaster name, such as \"#sandy,\" \"#hurricane,\" \"#haiyan,\" and \"#typhoonhaiyan\" [12]. In Japan, large-scale natural disasters, such as earthquakes and floods, are frequent. After a disaster, many people try to confirm the safety of their family and friends, usually by fixed-line and cellphone calls [13]. However, the communication infrastructure in Japan is often disabled for long periods after a large-scale disaster. For example, the Great East Japan Earthquake of 11 March 2011 caused extensive damage to communication infrastructures. After the earthquake, many fixed-lineand cellphone calls were disrupted. In many places, this situation persisted for a long time because the communication carriers took control of network traffic to prevent congestion. Immediately after the Great East Japan Earthquake in 2011 and the 2016 Kumamoto Earthquake, many people who were blocked from telephone communication by traffic congestion could access the Internet [14]. In this situation, Twitter was used for safety-information sharing, rescue requests, emergency alerts, and damage reports [15; 16; 17]. Similar situations occurred during recent disasters such as the 2017 Northern Kyusyu Heavy Rain Disaster and the 2018 Japan Floods [18]. Twitter has become an important tool for communicating safety information and rescue requests. To request a rescue on Twitter in Japan, the @TwitterLifeline account [19] suggests a rule as follows:  
* Victims should use the hashtag #\(\big{\langle}\)\(\big{|}\)\(\big{\rangle}\) (meaning #Rescue) and describe accurate and detailed information, such as the requirements, pictures, address, and location on the tweet. * When rescued, victims should report that they have been rescued and should immediately remove the rescue-request tweet that was previously posted. This rule was posted as a tweet on 11 September 2015 and 10 July 2018. During the recent major flood events, many tweets clarified the rescue needs of their posters using rescue request hashtags such as #\(\big{\langle}\)\(\big{|}\)\(\big{\rangle}\) (#Rescue) and #\(\big{\langle}\)\(\big{|}\)\(\big{\rangle}\)\(\big{\rangle}\)\(\big{\rangle}\)\(\big{\rangle}\) (meaning #Rescue_request). The effectiveness of tweets with these hashtags has been discussed [20; 21; 22]. To accomplish rescue activities based on the rescue request tweets in future disasters, we require a system that can effectively share such rescue requests as well as safety information. The above background highlights the need for a novel system through which victims can share their safety information, make rescue requests, and enable quick information gathering for decision making by local government staff or rescue experts. In this paper, we propose a Twitter-based safety confirmation system (T-@npi), a web application that can be accessed by any web browser or device connected to the Internet [23]. The name T-@npi derives from the Japanese word \"#\(\big{\langle}\)\(\big{\rangle}\) (pronounced anpi), meaning the degree of a person's safety. This paper introduces the operation of T-@npi and a preliminary operational test of the system.