At least 19 people were killed and around 25 injured after a crowd surge at a Durga Puja pandal in Kolkata on Saturday evening, once again putting the spotlight on the risks posed by very large gatherings and the systems required to manage them.The incident took place at the Chorbagan Sarbojanin Durga Puja pandal in north Kolkata amid heavy rain and a large congregation of pandal-hoppers. According to preliminary accounts from police and the state government, the rain prompted people waiting outside to move towards the pandal, while an announcement over the public-address system appears to have added to the commotion. People fell as the crowd surged, setting off a deadly crush. The exact sequence of events is being investigated.Such disasters are not unusual at large religious congregations in India. A 2014 report by the National Disaster Management Authority (NDMA), the apex body for formulating disaster-management policies in the country, noted that a “majority of the crowd disasters in India and developing countries have occurred at religious places”.So why do apparently orderly crowds suddenly become deadly, and what can administrations and organisers do to prevent this?What causes a stampede?What is commonly described as a “stampede” is often better understood as a crowd crush: a situation in which the density of people becomes so high that individuals lose the ability to control their own movement.Such situations can arise from structural problems — weak temporary structures, inadequate barricades or guardrails, poorly lit stairways, narrow entrances and exits — as well as fires, electrical failures, security scares and failures of crowd management.Also Read | 11 years ago, a warning at Kolkata’s Deshapriya Park that foretold a tragedyThe NDMA report identifies crowd control as central to preventing such disasters. Problems can arise when the actual turnout is much higher than anticipated; when more people are allowed into an area than it can safely accommodate; when there are inadequate holding areas outside entrances; or when entry and exit routes are too narrow or not separated.Story continues below this adWeak railings, insufficient queue-management systems and the absence of sectoral partitions can allow an otherwise manageable gathering to turn into one large mass of people.This is particularly important at events such as Durga Puja, where thousands of visitors may move from one popular pandal to another and arrival is not regulated through tickets or fixed time slots. Shoes and belongings of victims lay strewn in front of the pandal. (Premankur Biswas)The NDMA says inadequate arrangements can produce either panic or excitement, causing overcrowding or sudden acceleration in the movement of people. Once crowd density becomes very high, even a small disturbance — somebody falling, a barricade giving way, rain beginning suddenly or people changing direction — can have disproportionate consequences.Deaths in such situations need not occur because someone has literally been “trampled” under the feet of others. The NDMA notes that historically, compressive asphyxia has been the most common cause of death in crowd disasters: People packed tightly together are subjected to such pressure around the chest that they can no longer breathe.What appears to have happened in Kolkata?Story continues below this adWhile the investigation is yet to establish responsibility, preliminary accounts suggest several crowd-risk factors may have converged at Chorbagan.Police said there was a heavy crowd of pandal-hoppers when rain began in the evening. People waiting outside moved forward, some fell, and the crowd behind continued pressing ahead. The state government has also said that an announcement by organisers may have triggered or intensified the rush. Puja committee members and private security personnel have been detained as part of the investigation.18 dead in Kolkata pandal stampede where rain and rumour led to perfect stormRead: https://t.co/MN8ZLyE0pO https://t.co/mZpcfnBlmF— The Indian Express (@IndianExpress) October 17, 2026Reports have also drawn attention to the pressure around the pandal’s entry and exit points. Following the tragedy, the administration asked several other high-footfall Puja pandals to temporarily stop admitting visitors, underlining the importance of controlling the number of people present at a venue at any given time.The Kolkata tragedy therefore illustrates a fundamental principle of crowd management: what matters is not simply the total number of people attending an event, but how many people occupy a particular space at a particular moment, in which direction they are moving, and how quickly that space can absorb or release them.What role does crowd behaviour play?According to the NDMA report, understanding crowd behaviour is an important part of preventing disasters.Story continues below this ad“Individual behaviour in a crowd is sometimes influenced by the behaviour of others,” it says. Actions by a handful of people — for example, jumping a barricade or suddenly moving towards an exit — can lead many others to follow.This does not necessarily mean people behave irrationally merely because they are part of a crowd. Often, their behaviour is a response to the information available to them and to what people around them appear to be doing.Also Read | 12 detained, SIT formed to probe Kolkata Durga Puja stampede that killed 19For example, a long wait at a place of worship may prompt a few devotees to climb over fences. Others may follow, suddenly increasing the population in an area that was not designed to receive them.Announcements can similarly have unintended consequences. A message intended to disperse people or warn them of danger can cause a large number of people to move simultaneously unless carefully worded and accompanied by clearly managed exit routes.Story continues below this adThe NDMA also warns that inappropriate crowd-control measures can worsen an emergency. If police chase an unruly group in a direction opposite to an incoming stream of people, for example, the two flows can collide and produce a dangerous crush.Research on crowd behaviour has therefore increasingly favoured communication and community-based management over purely force-based control.What do earlier disasters tell us?Many of the weaknesses identified by the NDMA have recurred across major crowd disasters in India.At the Nashik Kumbh in August 2003, 29 pilgrims were killed. A magisterial inquiry identified pressure at barricades, the sudden movement of people in the reverse direction, processions of sadhus moving on elephants and vehicles along routes also being used by pilgrims, and the unexpected entry of pilgrims onto the route from several points.Story continues below this adAn even deadlier disaster occurred during the Kalubai Yatra at Mandhardevi in Wai, Maharashtra, in January 2005, killing 293 people.Also Read | Why crowds can frequently turn deadly in IndiaAn inquiry headed by Justice Rajan Kochar identified a combination of factors: incorrect estimates of the expected crowd; inadequate space around the temple; a narrow, steep and slippery approach; illegal vendors occupying the route, some with gas cylinders; inadequate security and firefighting arrangements; the absence of watchtowers and public-address systems; poor infrastructure; and lack of coordination among different agencies.The common thread is that crowd disasters usually do not have a single cause. Several weaknesses — excessive density, constricted movement, inadequate information, an unexpected event and poor coordination — combine until one trigger produces a sudden surge.How should crowd control work?The NDMA argues that most such disasters can be prevented through proactive planning and effective execution.Story continues below this adIts guiding principle is essentially one of managing demand and capacity: control how many people enter, regulate how they move while inside, and manage how they leave.Authorities must first estimate demand by examining previous attendance, the time at which people normally arrive, major attractions, special religious occasions and the profile of visitors.They must then calculate the capacity of the venue and, crucially, individual zones within it. A ground may appear capable of accommodating thousands of people, but a narrow lane, bridge, staircase or pandal entrance along their route may become the real bottleneck.Where demand exceeds capacity, the NDMA advocates “input control” — restricting or staggering entry.Story continues below this adAt shrines such as Vaishno Devi and Sabarimala, pilgrim registration and regulated access have been used to influence arrival patterns. Such systems are easier at destinations where visitors undertake a defined pilgrimage than at an urban festival such as Durga Puja. But the underlying principle remains applicable: authorities need mechanisms to slow or temporarily stop inflow when a site reaches safe capacity.At events where crowds cannot practically be regulated through registration, this can mean creating holding areas away from the main venue, one-way pedestrian routes, separate entrances and exits, real-time monitoring of crowd density and temporary closure of an attraction before dangerous congestion develops.At many religious sites, capacity cannot simply be increased because of geography, the structure of a shrine or religious practice. In such situations, the NDMA says, waiting is unavoidable — the task of authorities is to make that waiting safe.That requires adequate space, lighting, barricading, drinking water, medical facilities, trained volunteers, clear signs and public announcements that tell visitors where to go without creating panic.As a former NDMA official said: “A crowd should not be managed only after it begins to surge. The purpose of crowd management is to ensure that it never reaches the density and disorder at which a small trigger can become a catastrophe.”