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The Threat from Drones

in the Public Realm

The Threat From Drones In The Public Realm

By Michael Tomordy, Founder & Managing Director, Engage Asia


Drones, also known as Unmanned Aerial Vehicles (UAVs), have become increasingly common in both the commercial and military sectors over the last 15 years. Today, drones are widely available for purchase from retail shops or online by members of the public almost everywhere in the world.


The type, performance, availability and affordability of commercial drones is rapidly increasing, heightening potential dangers. Building owners, tenants and designers need to think about these threats in relation to commercial or public enterprises.


This paper will consider the threats and risks commercially available drones pose for commercial buildings, together with possible mitigation measures. It does not cover drone threats and mitigation measures that military and government security agencies have at their disposal.

An Emerging Threat 

The most common threats from drones are:

  1. CCTV surveillance reconnaissance

  2. Malicious intent (e.g. flying near or within an airport)

  3. Accidents from hobby drone pilots

  4. Criminal (e.g. transporting narcotics, delivering packages into prisons, disrupting business activities etc) 

  5. Terrorism (e.g. distributing poisons or other substance over a specific location, delivering improvised explosive payloads etc)

  6. Distributing objects/payload above target i.e. materials dropped into an HVAC plant on a roof (e.g. air ducts) or metallic foil into an electrical plant (i.e. terrorism or criminal)


Improved Capabilities

As well as being easier and cheaper to buy, drones continue to improve their capabilities.

  • Drones have expanded flight ranges and faster speeds, resulting in a greater standoff from a target as well as shorter detection and response times. (This presents a fundamental challenge. Target Hardening may be a more effective mitigation measure to counter a blast, or the distribution of poisons or chemical/biological agents, or CCTV surveillance.)

  • Drones can also carry heavier payloads (e.g. explosives, objects to be dropped etc)

  • Drones are easier to use and fly, including automated and pre-programmed flight paths and destinations without using GPS

  • Drones use more sophisticated software and firmware, which can be customised or hacked

Buildings are Not Designed for UAV Threats


Blast Mitigation. Most buildings today are designed for a blast-event by a vehicle or person at street level or a building’s lower levels. Common blast-mitigation measures for VBIED (vehicle-borne improvised explosive devices) include creating standoff, building perimeter blast walls, HVM (hostile vehicle mitigation) measures and adding blast-film to windows. For PBIED (people-borne improvised explosive devices), checks are undertaken at the perimeter or ideally outside the building.


HVAC Mitigation. Critical heating, ventilation and air conditioning (HVAC) plant equipment is often located on unprotected building roofs or on a building services floor inside. The installation is not typically designed to mitigate direct threats from the air. This can include objects or metallic foil or other substances ingested into air ducts or another plant, as well as a direct crash from a drone itself. Many organisations will be unable to operate without building services being operational. The risks and consequences are highest for critical infrastructure buildings or businesses/buildings reliant on MEP (mechanical, electrical and plumbing) capacity such as data centres.


UAVs, however, change everything. Buildings are designed to mitigate low-level blasts from a car/truck or person rather than from an airborne attack. UAVs can fly over a blast-wall, impacting, detonating or releasing substances at variable heights and locations (including the roof and an HVAC’s air-intake ducts for example). The classic use of standoff distance from blast location to the façade becomes irrelevant for a UAV threat.

A 5-10kg (or less) high-explosive charge can result in severe local damage and loss of life if detonated close to a façade glazing wall or window. A 5kg charge detonated 2 metres from façade glazing may result in:

  • Local façade breach/damage

  • Lung and ear damage to people

  • Fragmentation injuries

Designers need to consider blasts at height, including sacrificial glazing, double skin façade, and so on. 5kg is a relatively low weight and so the risk may be to softer targets.


Alternatively, the delivery of poisonous substances or chemical and biological agents could represent a greater risk and impact than a blast, as potential delivery over a wider area could result in greater casualties. Obtaining these agents may be challenging for terrorists, however.


Weapon-mounted UAVs, meanwhile, can be used for targeted assassinations, requiring ballistic glazing at key locations. However, these require considerable technical skill to deploy.


A UAV swarm attack, which could also be a diversion, is also possible. An attack from multiple UAVs could result in a more devastating impact that would also be harder to mitigate. 

Technical Countermeasures

The public sector generally cannot access the technical countermeasures used by military and security agencies. As a result, measures to minimise UAV threats usually relate to a building or facility design rather than electronic or kinetic counter-measures.

Technical countermeasures could include:

  • Geo-fencing, preventing a drone from entering an area/location by not allowing the GPS and UAV guidance system to function in that area

    • Manufacturers upload geo-fence data to drones. (Perhaps leading Chinese manufacturers can get CNI military locations in the US and UK from their government?)

  • Drone Detection Solutions that detect, identify, track and then stop drones, although no effective standards are available today

  • Jamming Technologies, although these are generally unavailable in the public sector, and also raise legal as well as safety implications

  • Kinetic Solutions such as nets or projectiles (known as birds of prey) that are fired at dones, although their effectiveness is questionable, especially for rapid response


What Governments Can Do

Governments are generally playing catch-up and have been late and slow in considering the threat from drones and, more importantly, how to mitigate that threat. 


The UK government is considering:

  • Policy changes such as drone registration for owners, licensing, training and safe flying areas

  • Regulation, law and penalties

  • Technical countermeasures and military response, especially for Critical National Infrastructure (CNI), although these are more difficult for other buildings and locations

  • Industry engagement


What Building Owners And Designers Can Do

A methodology for building owners and designers can include:

  • A Risk Assessment of a building, facility, assets and people, while identifying which assets, including people, to protect

    • A Vulnerability Assessment to detect possible launch sites and flight paths, with solutions to counter these, may also be relevant in some cases. Threats and vulnerabilities should also be compared, as blasts may be low probability while drones can represent a simpler but equally damaging threat

  • An Operational Plan

  • Detection Measures

  • Physical Mitigation Measures


Depending on the threats an organisation or building is facing, relevant responses could include:

  • Appropriate security engineering design with input to the design/project team

  • Relocating key functions/staff to less vulnerable locations in a building (and possibly away from good views in the best offices)

  • Revised blast mitigation, including a building’s upper levels or roof with a lower blast load then a VBIED

  • Protection for air-intake ducts

  • Protection for MEP plant equipment on a roof

  • Identifying and protecting other critical locations, plus mitigation of vulnerable locations

  • Enhanced window/glazing protection, including for counter-CCTV surveillance

    • For blast mitigation: ASF, blast curtains and blinds


The Future

The use of UAVs will evolve, particularly for illegal activities. Use in terrorist propaganda will also increase. More concerning are the larger payloads drones can autonomously deliver to pre-designated locations.

  • UAV threats will vary, depending on the country, city, location, building type and owner/tenant profile  

  • IEDs (improvised explosive devices) that can be used in drones are more readily available to terrorists, albeit a low probability threat for most organisations. The worst case scenario is using drones to distribute poisonous and other chemical and biological agents over a wider area, although obtaining chemical or biological or similar agents may be a challenge

  • All stakeholders need to take the threat from drones more seriously, including governments, building owners and tenants

  • Designers need to evaluate the threat based on individual buildings as well as the threat and risk profiles for different owners and tenants  


About Michael Tomordy

Michael is the founder and managing director of Engage Asia. He set up the company after working for Arup for 18 years, founding and leading both Arup’s IT & Communications practice and Arup’s Risk & Security practice in Asia. Michael is a Fellow of the Institution of Engineering and Technology (IET) and a Fellow and Engineering Supervisor for the Hong Kong Institution of Engineers (HKIE). In addition, Michael is on the UK Government Security Registry and is also a member of the US Government Overseas Security Advisory Council (OSAC).


About Engage Asia

Engage provides professional and trusted advice to private and public sector clients, consulting on information technology and digital services as well as security, risk and business resilience. Our specialists have worked with a broad range of companies on world-leading business, risk and design projects across the globe. We help realise new opportunities, manage risk and reduce costs, generating value and business resilience.

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