A lockdown is an emergency protocol that usually prevents people or information from leaving an area. The protocol can usually only be initiated by someone in a position of authority. Lockdowns can also be used to protect people inside a facility or, for example, a computing system, from a threat or other external event. Of buildings, a drill lockdown usually means that doors leading outside are locked such that no person may enter or exit. A full lockdown usually means that people must stay where they are and may not enter or exit a building or rooms within said building. If people are in a hallway, they should go to the nearest safe, enclosed room.
Procedures for using both emergency and preventive lockdowns must be planned.
A preventive lockdown is a preemptive action plan implemented to address an unusual scenario or a weakness in system to preempt any danger to ensure the safety and security of people, organisation and system. The focus for preventive actions is to avoid dangers and risks arising from the nonconformances to the normal circumstances, but also commonly includes improvements in efficiency.
Preventive lockdowns are preemptive lockdowns to mitigate risk. Most organisations plan for the emergency lockdowns but fail to plan for other situations which might quickly degrade to dangerous levels. These protocols must be based on the type of threat, and should be kept simple and short for quick learning and implementation, and flexible enough to handle several scenarios. This allows administrators more options to choose from which are easier to use in various scenarios. For example, in case of a loud scene by a parent or an unarmed petty thief being chased by the police through the school playground, this flexible procedure allows school administrators the flexibility to implement a more limited lockdown while teaching in school continues, this eliminating need for complete emergency lockdown, disruption and delays in resumption of teaching, etc. The consequences of not having procedures to implement such lockdowns is that the situation might quickly escalate where there could be loss of human lives.
Emergency lockdowns are implemented when there is imminent threat to the lives or risk of injury to humans, for example, a School's Emergency lockdown procedures must be kept short and simple to make them easier to use under real life crisis conditions. Simple procedures can be easily taught with periodic lockdown drills instead of lengthy training.
During the 2019–20 coronavirus pandemic, the term lockdown was used for actions related to mass quarantines. Lockdowns can limit movements or activities in a community while allowing most organizations to function normally, or limit movements or activities such that only organizations supplying basic needs and services can function normally.
Lockdown procedures vary by school district. Generally, a lockdown means that interior and exterior doors are locked, and all students and staff must remain in their location from the time the lockdown is announced. Windows are covered, and students stand at the back of the classroom or away from windows.
Since the Columbine Shooting in 1999, lockdown procedures in schools have been constantly changing. Some schools direct teachers to continue with standard procedures while remaining quiet, while some recommend an active approach against threats.
In its most common usage in corrections units, the term lockdown can be defined as a course of action to control the movement of inmates. Confining all prisoners, except workers, to their cells until the end of the day is an example of a "lockdown period" in a corrections schedule. However a "full lockdown" is used when all prisoners are locked in their cells to prevent prison riots or unrest from spreading or during an emergency.
In US guidelines, occasions for preventing entry into a hospital may include: power failure, earthquake, flooding, fire, bomb threat, hostage crisis and active shooter. Occasions for preventing both entry and exit from a hospital may include: external contamination, civil disturbance and abduction of an infant or child.
In manufacturing, the term lockdown event refers to a continuous improvement initiative in which manufacturing in a specific area (typically a cell or specific piece of machinery) is halted in order to contain, and determine, what are the issues that are preventing the manufacture of goods from meeting the quality specifications. During the lockdown event a multi disciplinary team reviews the specific area manufacturing processes, tooling and machine condition, to find the root cause(s) of the problem(s). Once changes to the process, or machine repairs that may include adjustments and/or replacement are effected, a sample run is initiated and evaluated. If the results of the validation are within the required specifications, the area lockdown is lifted and production is resumed. Follow up sampling is conducted subsequently to ensure continuity of the lockdown results.
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In December 2005, the New South Wales Police Force (NSW Police Force) initiated a lockdown of the Sutherland Shire and other beach areas of New South Wales to contain race rioting (and retaliative strikes).
An example of a campus/school lockdown was demonstrated at the University of British Columbia (UBC) on January 30, 2008, when an unknown threat was made and the Royal Canadian Mounted Police (RCMP) issued a lockdown on one of the buildings on campus for six hours, cordoning off the area, and a campus alert was sent via email to everyone affiliated with UBC while students and faculties were to remain locked in the building.
On April 10, 2008, two Canadian secondary schools were locked down due to suspected firearm threats. George S. Henry Academy was locked down in Toronto, Ontario at approximately 2:00 p.m. The Emergency Task Force (TPS) were contacted and the lockdown lasted for more than two hours. New Westminster Secondary School was locked down in New Westminster, British Columbia at approximately 1:40 p.m. The Emergency Response Team (ERT) were called and the school was under lockdown until 4:30 p.m. Due to the size of the school some students were not able to leave until 7:00 p.m.
On 19 April 2013, the entire city of Boston was locked down and all public transportation stopped during the manhunt for terrorist Dzhokhar and Tamerlan Tsarnaev, the suspects of the Boston Marathon bombing, while the town of Watertown was under heavy-armed police and SWAT surveillance, as well as systematic house-to-house searches.
In the 2015 Brussels lockdown, the city was locked down for days while security services sought suspects involved with the November 2015 Paris attacks. Later in 2015, a terror threat caused the 2015 Los Angeles Unified School District closure.
During the 2019–20 coronavirus pandemic, numerous governments responded to the disease with lockdowns of international borders and public spaces, including but not limited to China, Colombia, France, Italy, India, Malaysia, United Kingdom, United States. 
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