From time to time, there are sharp ups and downs of quotations on the stock exchanges. When a panic begins, the rate of decline can go through the roof. To prevent trading from turning into chaos, each exchange has its own mechanismIn extreme cases, stock exchanges close trading in the middle of the day or even immediately after opening. How and why do trading platforms do this?Suspensions of trading give investors the opportunity to understand what is happening in the market, learn information and make decisions based on market conditions, said Stacy Cunningham, president of the New York Stock Exchange, in an interview with CNBC.How does the NYSE stop trading?According to the rules of the New York Stock Exchange, if the S&P 500 index falls by 7% from the closing price of the previous day (level 1), trading will be stopped for 15 minutes. If the decline continues after this break and the index falls by 13% (level 2) before 15: 25 New York time, the exchange will suspend trading again for 15 minutes. After 15: 25, a 20% drop is allowed (level 3). Exceeding this threshold leads to a trading stop until the end of the day.On March 9, 2020, after the key US indices fell by 7%, an automatic "fuse" was triggered immediately after the start of trading, and trading was stopped for 15 minutes. This helped to stop the further decline in quotations. When trading resumed, the main stock indexes managed to break away from their lows and stay above them.These rules were developed after an instant technical collapse on the New York Stock Exchange in May 2010 (Flash Crash). The exchange adopted the latest version of the rules in February 2013.The days when trading stopped. 7 most unexpected pauses on the stock exchangesIf trading in the company's shares is suspended, it does not mean that the shares have become useless or their value has fallen to zero. In such cases, the exchange temporarily blocks trading until it determines what happened and whether there is a threat to bona fide investors. Trading may be suspended for individual shares or for all securities registered on the exchange.Crisis-97: minus 7% in five hoursOn October 27, 1997, the Dow Jones index fell by 7.18% (554 points) in five hours. Emergency sales on the US stock market began immediately after the collapse of the Hong Kong Stock Exchange indices by 6% due to the financial crisis in Asia.After the index fell by 4.54%, the exchange suspended trading for the first time for half an hour to calm the panic among the participants. It didn't help. After the resumption of trading, the decline continued and exceeded 7%. This time, the exchange stopped trading completely: traders were sent home before the end of the day. This decline was the largest intraday drop for the US market in ten years."Enron": from princes in the mudIn the nineties and the beginning of the two thousandth, the Enron energy company was a giant of American business. It ranked seventh in the United States in terms of capitalization. At the maximum, Enron shares were worth $90.75 apiece.In 2001, the company was accused of falsifying data in reporting. After that, the quotes began to fall. On December 2, 2001, Enron declared bankruptcy — and the securities collapsed to $0.26.The New York Stock Exchange (NYSE) soon stopped trading in these shares. As a reason for the suspension, the regulator pointed to the share price below $1 per share, which violates NYSE standards.Read more: What is the New York Stock Exchange (NYSE)When the exchange turned off the lightsIn March 2009, the Sydney Stock Exchange stopped trading after a serious power outage. About 70 thousand houses and administrative buildings, including the stock exchange building, were left without electricity. Due to the lack of electricity, traffic lights were turned off and many kilometers of traffic jams were formed. Some residents were stuck in elevators for a long time.It is interesting that two days before the power outage, residents of the city took a voluntary part in the "Earth Hour — 2009" campaign. They turned off the lights in their own apartments for an hour. The campaign was held by the World Wildlife Fund (WWF) to draw attention to climate change in the world.Blind tradingIn August 2013, the NASDAQ stock exchange, specializing in securities of high-tech companies, suspended trading in shares for three hours. This was due to a technical failure: the exchange stopped receiving applications from trading participants and displaying data on changes in quotations. Trading resumed only 35 minutes before closing time.On this day, the share price of the American company NASDAQ OMX Group, which owns the NASDAQ exchange and eight other European exchanges in the Baltic region, fell by 3.4%. The three-hour suspension of trading due to technical problems was the longest in the history of this exchange.Read more: About NASDAQ Stock ExchangeNon-flying planes, non-purchased sharesIn July 2015, the New York Stock Exchange, where shares of the world's largest corporations are traded, stopped trading in all registered securities for three hours. This was due to a technical failure, and the exchange canceled outstanding applications for securities transactions.The New York Stock Exchange resumed work by the end of the day. On the same day, there was a technical failure in the system of one of the largest American air carriers, United Airlines. The airline canceled all flights.An hour and a half of silenceIn September 2015, the Moscow Exchange suspended operations on the stock, currency, money and futures markets. The exchange's website also stopped working. This was due to malfunctions in the network equipment of the Moscow Exchange in the M1 data center.The exchange's clients could not connect to the systems and place orders in the usual mode. The exchange was restored in an hour and a half.Read more: What are futures: types, features, advantages and risksThe shortest trades in historyIn 2016, one of the trading sessions on the Chinese stock market lasted less than 30 minutes and became the shortest in the history of the Chinese market. The stock market fell after the decision of the People's Bank of China to sharply lower the yuan against the dollar.The Shanghai Stock Exchange Index Shanghai Composite Index lost 7%, falling to 3116 points, the Shenzhen Stock Exchange index Shenzhen Component fell by 8.35%, to 10,746 points. The CSI 300 composite index of blue chips lost 7.2%. In accordance with the rules in force at that time, due to such a decline in the CSI 300 index, trading on Chinese stock exchanges was suspended until the end of the trading day.Read more: "Blue chips" of the US ...