OHSA Series: Due Diligence Primer

Defenses to OHSA Charges

Introduction to Due Diligence 

Have you ever wondered what happens if your workplace faces charges under the Ontario Occupational Health and Safety Act (OHSA)or other similar legislation? What steps should you take, and what defences are available to you? Navigating these charges can be complex, but understanding the due diligence defence is crucial. This post breaks down the basics of strict liability offences under OHSA and introduces the due diligence defence—a vital strategy for employers. Whether you’re a business owner, manager, or employee, knowing how to handle OHSA charges can protect you from severe fines and potential jail time. This is the first in a series of posts aimed at demystifying the defences available under the OHSA.

What is Strict Liability?

Violations of Ontario’s OHSA, among other statutes, are categorized as strict liability offences. Essentially, strict liability means that parties facing charges under the OHSA are restricted in the substantive defences they can present to prove their innocence. Apart from procedural defences and strategies (which are crucial), and the often-unsuccessful defence of “officially induced error” (more on this later), parties charged with OHSA violations have one primary substantive defence: due diligence. Understanding this defence and other strategies is crucial for business owners as OHSA breaches can lead to massive fines and even jail time for individuals. 

What is Due Diligence?

Section 66(3) of the OHSA states:

“On a prosecution for a failure to comply with,

(a) subsection 23 (1);

(b) clause 25 (1) (b), (c), or (d); or

(c) subsection 27 (1),

it shall be a defence for the accused to prove that every precaution reasonable in the circumstances was taken…”

This section has been interpreted by the courts as establishing the availability of the due diligence defence for any strict liability breaches of the OHSA and its subordinate regulations. Moreover, in R. v. City of Sault Ste. Marie (City) (1978), the Supreme Court of Canada outlined the due diligence defence as follows:

“The defence will be available

(1) if the accused reasonably believed in a mistaken set of facts which, if true, would render the act or omission innocent, or

(2) if he took all reasonable steps to avoid the particular event.”

The first tier is known as the “mistaken fact defence.” It asserts that the defendant genuinely believed they were complying with the relevant OHSA provisions. It’s crucial to note that this defence does not apply to situations where the defendant simply did not know they were breaking the law – ignorance of the law is seldom a valid defence. The mistaken fact defence is rarely successful as it necessitates highly nuanced factual scenarios to justify breaching the OHSA.

The second tier is the essence of the due diligence defence. It states that despite breaching the relevant OHSA provisions, the defendant took every reasonable precaution to prevent the breach, and the breach occurred despite their best efforts. Naturally, the defendant faces a high threshold in proving that they did everything possible to avoid the breaches. However, the courts have clarified that defendants are not expected to be flawless in their due diligence efforts. Thus, mounting a defence against OHSA charges on these grounds is feasible if planned for and executed correctly.


Crucially, the entire due diligence defence, in Ontario, hinges on specific facts and demands a deep understanding of the law, the involved parties, and prevailing industry standards. Since OHSA convictions are provincial offences, they can result in substantial fines for corporations and individuals. Furthermore, individuals convicted under the OHSA can face jail time for serious charges. Hence, defending against OHSA charges is a serious matter that requires experienced legal counsel who is knowledgeable in the world of regulatory defence, specifically, OHSA defence. 

Stay tuned for more posts on this high-risk but little-understood area of employment law.

If you or your business require a better understanding of how to maintain compliance with the OHSA and/or defend regulatory charges, we would be happy to assist.

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