Invacuation to Shelters in Place – Key Considerations

A key objective of building security planning and design is to provide occupants with safe travel paths options for taking refuge inside internal shelters in place, or to exit the building as part of a wider site evacuation.

While building evacuation is a more familiar industry term as it relates to code mandated emergency egress that may be triggered by general life safety scenarios such as fire, building invacuation is a concept that is not as broadly adopted.

Invacuation is required where a security threat has a presence outside of the building and is advancing to breach the building envelope and ultimately target building occupants. In this scenario, occupants may not be able to egress a building due to the risk of exposure to the adversary and coming under attack.

Security threat vectors that may require building invacuation include a mob incursion, active shooter, or non-firearm weaponised attack.

A common question that arises is whether invacuation and evacuation routes can be the same or if they must be distinct. The following design and operational considerations assists in making this decision. 

1. Code Compliance

First and foremost, ensure that you are complying with the relevant building, life safety and accessibility codes in your country and state as they apply and govern building egress requirements. Throughout the planning process, ensure compliance is maintained after the addition of invacuation routes and shelters in place.

2.  Threat Characterisation and Modelling

It is imperative that invacuation and shelters in place provisions are proportionate to an accurately characterised security threat, including:

1. Attack methods and tools/weapons used.

2. Number of attackers.

3. Building entry points most likely to be exploited.

4. Specific occupants, user groups or building areas that may be targeted in an attack. This includes occupants that work in close proximity to high targeted value assets.

A threat assessment should form part of a wider security risk assessment for the building.

3.      Total Attack Delay Time

The total attack delay time refers to the time taken from the initial breach of the building envelope (or site perimeter, depending on the overall layout), to reaching the closest shelter in place. Ideally all building occupants should have reached a shelter in place during this time.

Estimating total attack delay time – this can be estimated by assessing the quantity, construction and materiality of building elements that would need to be breached by an attacker before reaching building occupants. If the attack is assumed to commence at the site perimeter then this includes time taken to breach perimeter walls, fencing and gates.

Maximising total attack delay time - by upgrading to products such as doors and windows that meet forced entry standards, the total attack delay time can, in principle, be extended to allow sufficient time for occupant to reach shelters in place. By confidently identifying the weapons and tools that would be used to breach a barrier, the correct forced entry rating for a building element in terms of delay time can be selected or specified. Example forced entry test standards that simulate a mob incursion include U.S. Department of State DoS SD-STD.01.01 and ASTM International ASTM F3038.

Other factors determine total attack delay time as well, such as the time taken to detect and respond to an attack.  This has been well documented by Sandia National Laboratories as the Adversary Task Time. 

4.      Identify Suitable Shelters in Place

Existing rooms that can serve as shelters in place should have the following provisions:

1. Sufficient space to accommodate the number of occupants on a building floor or area that need refuge, noting that there may be more than one shelter in place per floor.

2. Not have glazing or viewing panels, as these will provide the attack with a visual target. Where this is unavoidable, glazing should be forced entry rated.

3. Solid construction elements such as doors and walls should be forced entry rated.

4. Walls should extend to the upper slab, preventing incursion through the ceiling space.

5. Appropriate locksets, ironmongery and door hardware to resist forced entry. Sole reliance on electronic access control should be avoided as the system, software or network infrastructure may be compromised.

6. Provide a clean and filtered fresh air supply through a mechanical system independent of the rest of the building.

7. Dedicated electrical switchboard with a back up power runtime commensurate with the appropriate security response time.

8. Emergency communication links independent to the building telephony system for communicating with response personnel.

9. Surveillance monitor to view live footage of areas outside the shelter in place and the building.

10. First aid and medical equipment.

11. Depending on the anticipated response time, long life food and water rations may be required.

Shelters in place should be able to be used during business-as-usual mode for routine operations and working accommodation and be able to be secured during an invacuation.

Lastly shelters in place should not be obvious in terms of their use as a place of refuge and only known to legitimate building users.

5.      Identify Potential Dual-purpose Routes

By combining the findings of the threat assessment, estimating the adversary task time and nominating shelter in place locations, emergency egress routes that can also be used for invacuation can be determined. Specifically, the following factors should be considered:

1. Does this route provide optimal distance from the anticipated attack, including preventing visibility to the attackers?

2. Will this route provide sufficient time for occupants to reach a shelter in place before the adversary task time is complete?

3. Is the route wide enough to handle the anticipated flow of people and avoid congestion, considering that invacuation traffic may be higher than evacuation traffic at certain locations and times.

If possible, secondary invacuation routes should be provided for redundancy in case the primary route is blocked or an attacker is present.

Dual-use routes should be marked distinctly, indicating their purpose for both evacuation and invacuation.

Invacuation routes should align with broader emergency response plans and regular drills should be performed to familiarise occupants with invacuation routes and procedures.

Closing Remarks

Ultimately, it is advisable that requirements for invacuation and shelters in place be identified and implemented early in the building planning and design process, in coordination with architecture and relevant design engineering disciplines, and underpinned by a security, threat and vulnerability risk assessment.

For an existing building that is assessed at risk of an external security breach that is part of a threat trajectory to attack occupants, the feasibility of invacuation to potential rooms that can serve as a shelter in place should be undertaken, including desktop exercises to gauge the vulnerability of building occupants to an inward moving threat.