Canadian Consulting Engineer


January 1, 1999
By By George Fawcett, LRI

As one of Canada's few Modernist National Historic Sites, Canada's Cold War Museum known as the Diefenbunker has had many unique programming and operational challenges. The foremost challenge was with the occupancy capacity limit. The museum...

As one of Canada’s few Modernist National Historic Sites, Canada’s Cold War Museum known as the Diefenbunker has had many unique programming and operational challenges. The foremost challenge was with the occupancy capacity limit. The museum has only one means of egress to the surface – by way of the blast tunnel. This single exit route meant only 60 people at a time could visit the main building, which severely restricted the museum’s potential revenues and ultimately impacted the museum’s ongoing viability.

The application of the Ontario Building Code through an Alternative Solution allowed the occupant loading to be increased from 60 to 420 persons. This article describes the passive, active and procedural elements that were implemented. The Alternative Solution approach was necessary due to the construction difficulties and heritage aspects of the Diefenbunker. To comply literally with the code’s requirement for two exits each discharging separately to the exterior at grade was not practical, as numerous walls of the bunker are over 1-metre thick reinforced high-strength concrete.

Sanctuary during the Cold War

The Diefenbunker was constructed between the years of 1959 to 1961 for the purpose of maintaining the Government of Canada’s critical functions in the event of a nuclear strike during the Cold War era. The bunker is located approximately 35 kilometres northwest of the Parliament buildings in Ottawa, and its design and construction centred on the survivability of the building against close-range nuclear missile attack. In the event of an attack, the Diefenbunker was designed to house 525 occupants for a minimum duration of 30 days.

The bunker has hundreds of rooms that were intended to provide all the necessities of life in a highly sophisticated working environment. They include a command centre, medical operating rooms, a cafetaria and food storage facilities, bedrooms, a lounge, and a morgue.

Named after John Diefenbaker who was Prime Minister at the time the government decided to construct the facility, the site was owned and operated by the Department of National Defence from 1959 to 1994. Should nuclear war have broken out or seemed imminent, the Diefenbunker would have been the safe haven for those providing the thin thread of continuity of government.

For the 33 years it was in service the bunker housed day-to-day operations that made it the key strategic communications centre for the Canadian Forces. Then in 1994, the government sold the site to the local township of West Carleton (now part of the city of Ottawa). The local community rallied the municipality to allow them to run tours of the mysterious secret bunker. The initial tours were an overwhelming success! The community then worked successfully to have the facility designated as a National Historic Site of Canada. It was dubbed “the most important surviving Cold War site in Canada” by the Historic Sites and Monuments Board.

The community volunteers eventually won the right to buy the property and operate it as a permanent museum. The Diefenbunker opened its doors in 1998 in its new role as a not-for-profit charitable museum under community ownership.

Four underground floors and a tunnel access

The main building (the bunker) is four storeys and is constructed entirely below grade. It covers a building area of approximately 2,160 square metres on each of the four levels. Level 400 is the storey closest to ground level, with levels 300, 200 and 100 following beneath.

The bunker is connected to a separate large bank vault that was intended to house Canada’s gold reserves in the event of an attack. The corridor leading to the vault is accessed between the 200 and 100 levels.

A tunnel at grade leads down into the bunker’s Level 400. The tunnel is accessed from both the west and from the main visitor pavilion at the east. Three stairs serve all floor levels, and each stair discharges into Level 400. All occupants exited via the tunnel exit from Level 400.

In addition to the single tunnel exit, two chutes are located at Level 400. Each chute contains a ladder that is capable of providing emergency access to grade. However, access to grade is only possible by operating a lever which releases a 5-metre layer of gravel from above the ladder into a catch basin below the ladder. These ladders were provided as an exit of last resort for personnel within the Diefenbunker while it was in use by the government.

New fire safety program

The Diefenbunker was limited to an occupant load of 60 people. This limit was enacted in September 2000 because of the change of use to a Group A (assembly) occupancy (museum).

During a nuclear attack obviously no-one would want to evacuate outside, so the original design had subdivided each level of the bunker into five or six 3-hour fire compartments. The entire facility is built of non-combustible construction with all interior walls providing varying levels of fire separation.

LRI Fire Protection and Building Code Engineers were retained by the museum owner to review ways of allowing more visitors into the museum relative to the Ontario Building Code (OBC) requirements.

To achieve this, LRI developed an Alternative Solution under the new Objective Based OBC. A very preliminary program was developed and submitted to the Ottawa Building Department (authority having jurisdiction “AHJ”) to initiate a dialogue as this type of approach had never, to our knowledge, been attempted on a scale or application like the Diefenbunker. Subsequent meetings were held with the AHJ and a site visit was conducted.

The Alternative Solution, which involved the modification and use of existing and new active and passive fire protection systems, in our opinion provided sufficient compliance with the intent of the code.

The Alternative Solution was submitted to the AHJ and was accepted in the fall of 2008.

Providing additional exit routes

The solution provides robust life safety and property protection while balancing important considerations regarding the unique architectural, national, public interest and heritage aspects of the Diefenbunker.

To solve the problems with the exit, several changes were made.

First, existing corridors were upgraded to provide two fire-separated corridors that allow a means of egress at Level 400. The fire rating of the exit corridors on the 400 level had to be determined as a minimum 1-hour fire resistance rating was required.

Unfortunately, there were no details of the material composition of the prefabricated wall panels, and due to the historic designation of the building the walls could not be replaced. Sections of the panels therefore had to be sent to a testing lab for analysis.

After understanding the composition of the panels and how they were structurally supported, which involved an extensive evaluation of available data on archaic materials and fire tests dating back to the 1930s, we were able to determine that the walls provided the equivalent of a 1-hour rating. Many of the existing rated corridor doors had been compromised over time by the installation of viewing windows and louvres for air circulation. These doors and transoms were replaced.

Above the wall panels and suspended ceiling, the wall consisted of metal lathe and some type of plaster. Lab results indicated that it would not provide a 1-hour rating so this section of the wall had a spray-on fire proofing material applied to achieve the rating.

Second, the existing blast/entrance tunnel from Level 400 to grade was modified to provide two fire separated means of egress. This was done using rolling fire shutters that can be released manually or upon any alarm on the 400 level. For safety reasons the shutters have audible signals that increase in frequency to alert people of the i
mpending release. In addition, the rate of descent is controlled so the shutters do not come down too quickly. Two swing type doors are installed between the two rolling shutters in the blast tunnel to allow access to the east or west blast tunnel exit in the event the fire was in the blast tunnel.

New detectors, alarms and other upgrades

The upgrade included many other features:

  • the existing fire alarm system was replaced and upgraded with smoke detectors along the primary corridors;
  • a sprinkler system was installed throughout the building and blast tunnel;
  • the existing standpipe system was upgraded to include additional cabinets and a new riser for water supply;
  • for the fire protection water supply, an electric fire pump was added and three concrete water tanks were relined;
  • new and upgraded emergency lighting and exit signage was installed;
  • an emergency power generator was installed; it was connected to the fire pump and emergency lights and exit signage;
  • asbestos was removed in two locations, the main lobby and War Cabinet Room; this was type 3 asbestos removal, which involved sealing off and ventilating the areas, and providing showers to decontaminate the workers;
  • a Fire Safety Plan was prepared.

Fund-raising and construction challenges

During the design phase, the Diefenbunker’s executive director worked long hours with assistance from LRI to obtain funding for the retrofit. Almost the entire $2-million price tag was raised from approximately 10 government ministries and private foundations. For those who have never had the pleasure of this exercise, Wow! — it sure is a lot of paper work! Having said that, this project would never have come to fruition without their generous support.

The project was awarded in the summer of 2009. The construction process required dedicated and skilled trades as it was not easy accessing the hundreds of rooms in the bunker. What made this so much more difficult was the fact that the bunker was designed to withstand a nuclear attack and thus many of the walls were greater than 1 metre thick and made of a top secret formula of hardened concrete with rebar up to 5.7 cm in diameter.

Completed in the summer of 2010, the Diefenbunker can now accommodate up to 420 visitors and has a bright and sustainable future.

This project was challenging but also interesting, and it shows that we can save our historical sites and keep a part of our heritage alive for future generations. From the Diefenbunker’s perspective, we can always say that it truly is a “Blast from the Past.” cce

George Fawcett is a vice president and Ottawa branch manager with LRI Fire Protection & Building Code Engineers.

Owner:Diefenbunker, Canada’s Cold War Museum, Ottawa, Ont.

Project lead, fire suppression and alarm system upgrades:

LRI (George Fawcett, CET)

Architecture, emergency power upgrades:

J.L. Richards & Associates (Nicolas Rivet, P.Eng., George Chinkisky, P.Eng., Marsh Frere)

Asbestos removal:

Envir-0-Health Solutions

General contractor:

Waterdon Construction



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