A Twitter analysis by the Centers for Disease Control and Prevention has confirmed that people were terrified when they were alerted that a ballistic missile was hurtling toward Hawaii. But when they learned that the alert was actually a false alarm, they were livid.

It’s something that people watching social media would have already guessed, but this analysis could help emergency management agencies send better alerts in the future. (Step 1: Don’t send false alarms about nuclear missiles.) The communications disaster unfolded last January when a series of major mistakes sent a terrifying alert to the phones and televisions of Hawaii’s residents. It said a ballistic missile was on its way to the islands, and people needed to seek shelter. It took a full 38 minutes for the alarm to be retracted, during which time people posted on Twitter in droves.

One of the key themes that emerged in the aftermath was that some people didn’t know what to do during a ballistic missile attack, according to the new CDC paper published in the Morbidity and Mortality Weekly Report. The findings tell public health officials that social media is a good place to reach people during a crisis, and future emergency alerts need to have clear instructions for what people should do. In a radiation emergency like a nuclear missile attack, those instructions are to “get inside, stay inside, and stay tuned,” according to the CDC. Of course, that doesn’t help prevent false alarms, but that’s another story.

In today’s study, the researchers searched for tweets — or, as they helpfully explain, “(Twitter postings)” — from the morning of the false alarm. The team specifically looked for tweets containing the words “missile and Hawaii,” “ballistic,” “shelter,” “drill,” “threat,” “alert,” or “alarm.” They ended up with more than 127,000 tweets. Of those, most were retweets and quote tweets, which they excluded to keep the information to a manageable amount.  

They ended up with more than 14,000 tweets sent during the 38-minute span when people thought the missile alert was real and in the 38 minutes after it was revealed to be false. Right after the alert went out, people voiced their shock, shared the missile alert with others, and tried to figure out what was going on. People tagged in military and intelligence accounts, the media, and told their families they loved them.

After the alert was retracted, the tone changed: people were pissed, and they vented their frustration on Twitter. The study included some highlights, although it redacted the profanity: “How do you “accidentally” send out a whole [expletive deleted] emergency alert that says there’s a missile coming to Hawaii and to take cover. AND TAKE THIRTY MINUTES TO CORRECT?!?” Some said they’d have trouble trusting future emergency alerts. And others said they hadn’t known what to do when they were told to seek shelter: “my friend & i were running around the hotel room freaking out because HOW DO WE TAKE SHELTER FROM A [expletive deleted] MISSILE?!”

While the tweets offer a window into that frantic hour and 16 minutes, it’s hard to know from those reactions on social media what people in Hawaii were really thinking, according to David Alexander, a professor of risk and disaster reduction at the University College London, who was not involved in the study. “At present, it is virtually impossible to answer the question, using social media, as to what is the consensus view on a problem,” he told The Verge in an email.

Still, the fact that there was confusion in response to the missile alert could help emergency management agencies send better alerts in the future that include clearer steps people can take to try to protect themselves, says Bhavini Patel Murthy, a lieutenant commander with the US public health service and the study’s lead author. “We learned we need to make sure that our messages are clear so that people know what to do in an emergency,” she says. “We want to make sure we get the right message out at the right time.” Here’s hoping that no one needs to try out the “right” missile alert anytime soon.