The Due Diligence Defence in Ontario Construction: What Your Records Have to Prove

This is general information, not legal advice. If you are facing a charge or investigation, get a lawyer.

If a worker is seriously hurt on your site, the due diligence defence is the one Ontario construction employers reach for — and what your records prove often carries much of the weight. Under the Occupational Health and Safety Act (OHSA), most charges do not turn on whether you meant well or whether the injury was a freak event. The outcome is fact-specific, but it usually depends heavily on whether you can show, after the fact, that you took every reasonable precaution before it. This article walks through how that defence works, who carries the burden, and why a signature collected in the morning rush documents less than a dated record of what a worker understood.

Start with the stakes.

The numbers that define the worst day

Three figures every Ontario contractor's owner and director should know cold:

CA$2,000,000 — the maximum fine per offence for a corporation under OHSA section 66, in force since October 26, 2023 (Bill 79, Working for Workers Act, 2023). It is the highest corporate OHS fine in Canada.
CA$1,500,000 — the maximum fine for a director or officer of a corporation, per contravention, with up to 12 months imprisonment. Other individuals face up to CA$500,000 and up to 12 months imprisonment.
CA$500,000 — the mandatory minimum fine for a corporation convicted of a second or subsequent offence, within a two-year period, in which a worker is killed or seriously injured. In force since December 19, 2024 (Bill 229, Working for Workers Six Act, 2024). It is a floor: the judge cannot go below it.

Behind the OHSA sits Criminal Code section 217.1 — the Westray amendment — which places a legal duty on everyone who directs how work is done to take reasonable steps to prevent bodily harm. That is not a fine — and, on its own, it is not an offence either. It is a duty that can become relevant in a criminal-negligence prosecution of the people running the job — though negligence causing death or bodily harm still has to be proven under the Criminal Code, not merely the duty breached.

That is the legal environment your training and briefing records live in. It is worth asking, on a calm day, what those records would actually be worth in the event of a serious injury or fatality.

Strict liability: why the Crown does not have to prove intent

Most OHSA offences are strict liability offences. That has a precise meaning, and it is the hinge of the whole thing.

In a strict-liability prosecution, the Crown does not have to prove you intended any harm, or that you were reckless, or even that you knew about the hazard. The Crown must still prove the elements of the offence beyond a reasonable doubt — the physical facts: that the violation happened and that you were the employer, supervisor, or constructor the Act made responsible. What it does not have to prove is fault. Once the Crown proves those elements, the burden shifts to you.

This framework comes from the Supreme Court of Canada's decision in R. v. Sault Ste. Marie (1978), which put public-welfare offences like workplace safety into the strict-liability box. The trade-off is the reason the defence exists at all: because the Crown need not prove a guilty mind, the accused is given the chance to prove diligence instead.

The reverse onus: you prove the system, not the Crown

Here is the part that surprises owners. In an OHSA prosecution, you carry the burden of the defence. This is a reverse onus.

To make out due diligence, you must prove — on a balance of probabilities, the civil standard, not the criminal "beyond a reasonable doubt" — that you took every precaution reasonable in the circumstances. That phrase is not marketing language; it echoes the general duty in OHSA section 25(2)(h) and the reasonableness standard the courts apply.

Break that down into what it demands of a construction employer:

Every reasonable precaution. Not the easy ones, not the cheap ones — every precaution that was reasonable in your circumstances. The standard is reasonable care, not perfection. If a low-cost, available step would have addressed the hazard, its absence is hard to explain.
Reasonable in the circumstances. The court looks at your specific site, trade, and hazard — not a generic checklist. The standard rises as the risk rises and as better controls become available and affordable.
You prove it. The Crown proves the elements of the offence beyond a reasonable doubt; you prove the system that should have prevented it was real and running. If you cannot, the defence is much harder to make out even where you genuinely did the right things — because a defence you cannot evidence is a defence you may not be able to prove.

Contemporaneous records versus the morning-rush signature

Due diligence is proved with evidence, and not all evidence is equal. Documentation created at the time is generally more useful than a record reconstructed after an incident. A contemporaneous record — made in the ordinary course of work, before anything went wrong — does not invite the obvious cross-examination that a reconstructed one does: when did you actually write this?

Now look at the standard exhibit. A worker is seriously hurt by a hazard that was on that morning's Job Safety Plan (JSP). Your evidence that you addressed it with him is his signature — collected in the morning rush, on a sheet alongside a dozen others. A sign-in sheet like that can support that the worker was present or acknowledged the briefing, but on its own it ordinarily does not show much more:

It records his presence or acknowledgement, not that he was listening.
It does not by itself document that the briefing covered that hazard in any depth — the sheet has a topic line, not content.
It does not show he understood. Where English is not a worker's first language, whether and how comprehension was checked could be questioned, and the sheet does not answer it.
It looks the same as every other signature collected every other morning, so on its own it does not document what was actually done that day.

"Every precaution reasonable in the circumstances" is the test. Where a short, practical check of understanding was available and reasonable, a signature that only records attendance does less to show it was taken. This is the same distinction that separates attendance from understanding: a signature on a sign-in sheet, on its own, does not document how understanding was checked.

Section 217.1: the people who direct work have personal skin in it

The Westray amendment, Criminal Code section 217.1, is short and blunt: everyone who directs how another person does work has a legal duty to take reasonable steps to prevent bodily harm to that person. It was Parliament's response to the 1992 Westray mine disaster. The section itself creates a duty, not an offence: a criminal-negligence charge against an organization or the individuals directing work still has to be proven under the Criminal Code's negligence provisions — including that the conduct caused the death or bodily harm — with the section 217.1 duty as the reference point for what reasonable steps were owed.

For a specialty sub, that means the people who had authority to direct how the work was performed are not bystanders to the safety system; their own diligence can be in issue too. A briefing record that shows a supervisor did not merely hold the talk but confirmed it landed may help document one step that person took toward the reasonable steps section 217.1 asks about — not, on its own, proof of that individual's diligence.

What stronger evidence looks like

Flip the exhibit. Imagine producing this instead of a sign-in sheet: a dated, per-worker record showing that on the morning of the incident, the worker was briefed on that specific hazard, worked through a short guided dialogue about it, explained the hazard and its controls back in his own words, and was scored as comprehending — with the transcript attached. Where he had struggled, the record shows the gap was caught, retrained, and re-checked: gap found, gap closed, recorded.

That is contemporaneous evidence of a system that verifies understanding — one that runs every day, in the ordinary course of work, not one assembled for the courtroom. For a worked example of what that kind of record looks like laid out end to end, see the evidence-story example.

Be clear about what such a record does and does not do. No record wins a case or guarantees a defence. A court weighs everything — the physical facts, the reasonableness of the precautions, the whole context. What a per-worker comprehension record can add is one form of contemporaneous evidence the morning signature does not supply: a dated, attributable record of how you checked whether the person understood the hazard that later hurt him. How much weight it carries in a proceeding will depend on the record's reliability and all the surrounding facts.

This is also why records can be important, but they are never sufficient on their own. In R. v. Greater Sudbury (City), 2024 ONSC 3959, an Ontario court found a defendant had exercised due diligence despite a fatal construction incident — weighing its degree of control over the site, whether it had delegated to a competent constructor, how it evaluated that contractor, and how it monitored and supervised the work, rather than any single document. The Court of Appeal denied the Crown leave to appeal on March 31, 2025, ending the case with that finding intact. A comprehension record is one input into that kind of fact-specific assessment, not a substitute for it. Hicks Morley's review walks through the decision and its final outcome.

The honest objection

"If I measure comprehension, don't I create a record of the gaps I find?" It is the right question. The answer is that the gap exists whether or not you measure it. What you control is whether your file shows gaps found and addressed before the incident, or shows nothing. A record of gaps found and addressed documents a system that was actually looking; an empty file does not.

Frequently asked questions

What is the due diligence defence under Ontario's OHSA?

The due diligence defence is the response available to an employer, supervisor, or constructor charged with a strict-liability offence under Ontario's Occupational Health and Safety Act. Because these offences do not require the Crown to prove intent, the accused is given the chance to avoid conviction by proving, on a balance of probabilities, that they took every precaution reasonable in the circumstances to prevent the contravention. It comes from the Supreme Court's decision in R. v. Sault Ste. Marie and is proved with evidence of a real, functioning safety system — not with an after-the-fact explanation.

Who has the burden of proof in an OHSA prosecution?

The burden is split, and it reverses partway through. The Crown must prove the physical facts of the offence — that the violation happened and that the accused was the responsible party — beyond a reasonable doubt. Once that is proven, the onus shifts to the accused, who must then prove the due diligence defence on a balance of probabilities. This reverse onus is why your records matter so much: you, not the Crown, have to prove that reasonable precautions were taken.

What are the maximum penalties under the OHSA in Ontario?

Since October 26, 2023, a corporation can be fined up to CA$2,000,000 per offence — the highest corporate OHS fine in Canada. A director or officer can be fined up to CA$1,500,000 and any other individual up to CA$500,000, each with up to 12 months imprisonment. Since December 19, 2024, a mandatory minimum fine of CA$500,000 applies to a corporation convicted of a second or subsequent offence, within two years, in which a worker is killed or seriously injured. Confirm current figures with counsel.

Do contemporaneous safety records help a due diligence defence?

Documentation created at the time is generally more useful than a record reconstructed after an incident, because contemporaneous records are harder to dispute and were not made with a charge in mind. A dated, per-worker record of what a worker was briefed on and whether he understood it is that kind of evidence. No record guarantees a defence — a court weighs everything — but a contemporaneous, attributable record of how understanding was checked can add information a signature that only records attendance does not, with its weight depending on the record's reliability and all the surrounding facts.

What is the Westray duty and how does it affect supervisors?

The Westray duty is Criminal Code section 217.1, added after the 1992 Westray mine disaster. It places a legal duty on everyone who directs how work is done to take reasonable steps to prevent bodily harm. The section creates a duty, not an offence: a criminal-negligence charge against an organization or a directing individual still has to be proven under the Criminal Code, including that the conduct caused the death or bodily harm. For a construction sub, it means people who had authority to direct how the work was performed can have personal exposure, so a record that shows a supervisor confirmed a briefing was understood, rather than merely delivered, may help document one step that individual took — not, by itself, prove their diligence.

See your crew's comprehension, not their signatures.

Dashpot runs a five-minute verified-comprehension dialogue with every worker, every morning — built on the JSP your site already produces. We're onboarding a small number of Ontario pilot contractors.

Request a pilot conversation