The Heron Road Bridge Disaster

10 August 1966

Heron Road forms part of one of the busiest, east-west arteries in Ottawa. The four to six lane, divided thoroughfare runs from Walkley Road in the east, crosses the Rideau River and the Rideau Canal, where it becomes known as Baseline Road, and ends at Richmond Road in the west. Of the thousands of commuters that use the road each day, few are probably aware that the bridge over the river and canal was the location of the worst industrial accident in Ottawa’s history. On 10 August 1966, a span of the Heron Road Bridge, which was then under construction, collapsed while 60 workmen were pouring concrete on a segment of the southern, eastbound roadway. Seven men were killed on the scene, crushed under tons of falling concrete. Another man died later than day, while a ninth victim succumbed to his injuries a month after the horrendous accident. A further fifty-seven men were injured, many severely. Victims were trapped in a horrifying mess of solidifying concrete, tangled ironwork and splintered wood that made extracting them difficult.

Picnickers who had been listening to a rock n’ roll band in nearby Vincent Massey Park that hot, sultry afternoon, described the collapse of the bridge as sounding like a low-flying, jet airplane. So great was the impact that the seismograph at the Dominion Observatory three kilometres away on Carling Avenue registered the event at 3.27pm. Some eyewitnesses likened it to an exploding bomb. The loud roar of the collapse was accompanied by a large cloud of dust thrown up into the air.

Heron Bridge

Heron Road Bridge After The Collapse, 1966

Immediately, passersby, police, workmen from nearby work sites, and firemen descended on the disaster scene to help rescue the casualties, many digging in the wet concrete using only their bare hands. There was blood everywhere. Aiding the injured was perilous; a slab of semi-hard concrete overhung the disaster site. The Civic Hospital set up a triage station, with the injured ferried to hospital by ambulance, trucks, and police cars. Disaster relief continued after dark; in the early hours of the following morning, a heavy rain made rescue conditions even more treacherous. On the scene throughout the recovery operations was Ottawa’s Mayor Don Reid. Rev. Georges Larose, the Ottawa Fire Department’s chaplain, comforted survivors, and administered the last rights to victims as they were recovered. The Salvation Army distributed sandwiches, coffee, and cold drinks.

One survivor, Jorge Veiga, was stuck in wet concrete up to his neck. Rescuers carefully washed the hardening mess that threatened to suffocate him from his nose and mouth with water, while welders cut through the iron reinforcing rods that trapped his body. A bucket brigade was organized to keep the metalwork cool enough that the heated metal from the blow torches didn’t burn him. Thankfully he was successfully extracted without his rescuers having to resort to amputation as earlier feared. Another worker, Thomas Daly, was impaled, and was transported to hospital with an iron rod protruding from his arm. Fate was capricious. A nineteen-year old man amazingly survived the sixty foot fall from the bridge with only a slightly injured arm; his glasses landed beside him intact.

Work on the Heron Road Bridge had commenced early the privious year. In February 1965, the City of Ottawa signed a contract with Beaver Construction (Ontario) for the construction of footings for the reinforced concrete piers on which the Heron Street Bridge would rest. This work was successfully completed without mishap by June 1965. The contract for building the two three-lane bridges, (the northern bridge for west-bound traffic and the southern bridge for east-bound traffic), each 877.5 feet long made of pre-stressed concrete, was awarded to O.J. Gaffney Ltd in August 1965. The City of Ottawa also hired the firm M.M. Dillon & Company Ltd as consulting engineers to help design and supervise the Heron Bridge Project.

Work began in the fall of 1965 starting at the western end of the twin bridges. Each bridge was divided into four spans—PT1N (meaning post-tensioned, 1st span, north bridge), PT2N, PT3N, PT4N, and PT1S, PT2S, PT3S, PT4S for the south bridge. The concrete used to construct each span of the bridge decks was poured in two layers.  By August 1966, the western half of the twin bridges (PT1N, PT2N and PT1S and PT2S) was essentially complete. The contractor had also constructed the wooden falsework (the temporary supporting structure or scaffolding) to support the eastern spans (PT3N, PT4N, PT3S, and PT4S) as they were built. A month prior to the accident, the first layer of concrete, 217 feet long by 50 feet wide, had been poured over spans PT3N and PT3S. Disaster struck while the second layer of concrete was being poured on span PT3S. According to the Ottawa manager of M.M. Dillion, the consulting engineers, as workers poured the concrete starting from the centre of the span moving east, the single-layer section of the span that overhung the western end of the span flipped into the air, pancaking onto the rest of the bridge, bringing it down.

Immediately, the Ontario Government launched an inquiry into the disaster. Ontario’s supervising coroner Dr H.B. Cotnam hired the engineering firm H.G. Acres Ltd to assist him in his investigation of the causes of the collapse. The focus of the inquest was the factors that led to the death of Clarence Beattie, a foreman who died in the collapse, though the inquiry’s findings were applicable to all nine fatalities. A five-member Coroner’s jury met in late November 1966 to hear the conclusions of the investigating engineers, and to listen to the testimony of witnesses. Jury members quickly focused on the strength and stability of the wooden falsework used to support the bridge while the concrete spans were being poured. Of particular interest was whether the falsework, which lacked diagonal, longitudinal bracing, was able to support the bridge while under construction. The overwhelming consensus of professional opinion was to the contrary. To help demonstrate the weakness of such a design, Prof. Carson Morrison, head of the department of civil engineering at the University of Toronto, demonstrated the relative strength of braced and unbranced falsework using two wooden models.

After seven days of testimony from H.G. Acres Ltd and other witnesses, the jury reached its verdict. It concluded that Clarence Beattie died from being crushed, his injuries due to the failure of the falsework, and his subsequent entanglement in steel bars and cement. The jury also concluded that the failure of the falsework was due to the absence of diagonal, longitudinal bracing. Indeed, the jury contended that the falsework had been technically inadequate to even support the first layer of concrete that had been poured a month prior to the disaster. The jury also pointed to secondary factors, including the use of poor quality lumber in the construction of the falsework, as well as the differential settling of footings, and a temporary overloading of certain posts. However, the jury concluded that these secondary factors would not likely have caused the falsework structure to fail. The jury blamed both O.J. Gaffney, the construction firm, and M.M. Dillion, the firm of consulting engineers, for the bridge’s collapse.

As with all disasters, the Heron Road Bridge failure reflected a number of things that had gone wrong, any one of which if caught earlier might have averted the bridge’s collapse. Most importantly, there was confusion over the design of the falsework. There had been three different sets of plans owing to changes demanded by the consulting engineers. Although the second draft plans of the falsework had contained diagonal longitudinal bracing, the third set did not. Testimony at the inquiry indicated that the consulting engineers viewed the third design plan as supplementary to the second design plan, whereas the construction team viewed the third design plan as complete.

There was also conflicting testimony about the falsework itself. Robert McTavish, the chief engineer of the construction firm, testified that the bracing had been dropped from the third design plan following discussions with Victor J. Bromley, the project engineer from M.M. Dillion, since a different “system” had been included as a substitute. This system was not, however, included in the final plans which McTavish approved, nor was it built.  Bromley, on the other hand, denied that he ever agreed to the removal of the diagonal, longitudinal bracing.

Regardless of who was right, neither McTavish nor Bromley had an adequate explanation for why they both failed to notice that the falsework was inadequately braced. McTavish said “he was interested in something else.” Bromley held himself “guilty” for not noticing the absence of the bracing despite regular visits to the work site. He testified “I didn’t notice it. I can’t explain it. My mind must have been confused at the time.”

Heron Bridge today

Heron Road Bridge, Looking West, cirica 2012

While city and provincial safety inspectors had noted the absence of diagonal longitudinal bracing in the falsework structure when they had been taken on a tour of the worksite by an engineering student who had been recently hired by the construction company, they had been satisfied with the student’s response that the falsework design had been approved by qualified engineers. “If it’s good enough for them (the consulting engineers), it’s good enough for us,” the inspectors were reported to have said. They did not to raise their reservations with their superiors, or with qualified engineers from either the construction firm or the consulting engineering firm. Later, it came out that neither inspector was a trained engineer. Moreover, they had been instructed not to question decisions made by professional engineers.

Despite the jury’s findings of human error, it may not have discovered the root cause of the disaster. Behind most cases of human error lies a design error says Don Norman, Professor of Applied Psychology at the University of California, San Diego. Several issues may not have been sufficiently probed. Why, for example, did the many professional engineers employed by the construction firm and the consulting engineering firm fail to spot the design flaw in the plans for the falsework? Why did they subsequently fail to spot the absence of adequate falsework bracing despite on-site supervision and frequent inspections? With so many engineers involved, was it a problem of “if everybody is responsible, nobody is responsible?” Was it difficult for one professional engineer to question the work of another? Why did the city and provincial safety inspectors fail to report their concerns about the absence of diagonal, longitudinal bracing to their superiors? Did they see themselves as being inferior to professional engineers, and hence unqualified to raise concerns? Were the safety systems put in place to avert disaster themselves flawed?

The jury made a number of recommendations to reduce the possibility of future disasters. It recommended that there be a clear definition of the responsibilities of the building contractor and those of the consulting engineers. In addition, it advised that approved design and construction drawings for falsework be stamped by a qualified civil engineer, and that safety inspectors be better trained, and be required to make written reports regarding any area of the falsework which in their personal opinion was inadequate. The jury also urged that graded lumber be used in building falsework, and that a mandatory building code be developed by the province of Ontario for the construction of bridges and falsework.

The collapse of the Heron Street Bridge led to major improvements to Ontario’s building code. Robert McTavish, the chief engineer of O.J. Gaffney, the building contractor, and Victor J. Bromley, the project manager from M.M. Dillion, the consulting engineering firm, were both suspended from practicing as engineers in Ontario by the Association of Professional Engineers of Ontario for a period of one year. Bernard Houston, the chief estimator for Gaffney, who took responsibility for the majority of the design calculations for the bridge, was reprimanded. O.J. Gaffney was found guilty on two charges levelled under the Construction Safety Act, and was fined $5,000, the maximum penalty under the law at that time. The widows of the nine men who died in the Heron Bridge collapse received lump-sum compensation of $300 each (a little over $2,000 in today’s money), and a widow’s allowance of $75 per month, and an additional $40 per month for each child.

In 1987, the Canadian Labour Congress dedicated a memorial to those who lost their lives in the collapse of the Heron Street Bridge. The memorial, which lists the names of the nine workers who died in the disaster, can be found in Vincent Massey Park, close to where the fatal accident occurred.

 

Sources:

Kardos, G. 1969. Heron Road Bridge, Engineering Case Library, Leland Stanford Junior University, California, https://archive.org/details/ECL-133.

Globe and Mail (The), 1966. $250,000 estimated as compensation cost,” 20 August.

————————–, 1967. “Bridge builder charged in Heron road collapse”14 Janaury.

————————–, 1968. “Two suspended in fatal collapse of new bridge.” 27 January.

Ottawa Citizen (The), 1966. “Engineer Takes Blame,” 24 November.

————————–, 1966. “Bridge mock-up is sent crashing at inquest,” 25 November.

————————–, 1966. “Inquest jury pins blame on two firms,” 30 November.

————————–, 2006. “The day the bridge came tumbling down.” 5 August.

Montreal Gazette (The), 1966. “Nine Dead in Ottawa Disaster, 11 August.

Norman Don, 2013. The Design of Everyday Things,” New York: Basic Books.

Winnipeg Free Press, 1966. “Span that collapsed at western end of the eastbound lane between two 60’ abutments that remained intact,” 11 August.

Images:

Heron Road Bridge after the collapse, 1966, Workers’s Heritage Centre, http://whc-cpo.ca/albums/heron.html.

Heron Road Bridge, Looking West, circa 2012, Pomerleau,  http://www.pomerleau.ca/construction-contractor/Projects/555/49/Heron-Road-Bridge-Reconstruction.aspx.

 

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