To successfully rely on this defence, an employer must show that it has taken all reasonable precautions in the specific circumstances of the workplace to prevent injuries or accidents from occurring.

The leading case on strict liability offences is the Supreme Court of Canada's decision in R. v. Sault Ste. Marie (City). The Supreme Court found that offences under Ontario's Occupational Health and Safety Act were strict liability offences, stating: "In this doctrine, it is not up to the prosecution to prove negligence. Instead, it is open to the defendant to prove that all due care has been taken. This burden falls upon the defendant as he is the only one who will generally have the means of proof. This would not seem unfair, as the alternative is absolute liability, which denies an accused any defence whatsoever. While the prosecution must prove beyond a reasonable doubt that the defendant committed the prohibited act, the defendant must only establish on the balance of probabilities that he has a defence of reasonable care."

The burden of proof is placed on the employer. The employer must prove - on the balance of probabilities - that it took all reasonable steps to prevent similar incidents from happening.

Further, Section 25(2)(h) of Ontario's Occupational Health and Safety Act, in effect, requires all employers to act with due diligence. It states that "...an employer shall...take every precaution reasonable in the circumstances for the protection of a worker."

In R. v. Canada Brick Ltd., Justice Hill, when considering Section 25(2)(h), stated: "An employer is not legally bound to provide the safest imaginable workplace. While it may strive to do so, what the Act requires is compliance with those regulations which shape a reasonably healthy and safe work environment. Certain minimally prescribed standards seek to prevent accidents on account of worker inadvertence. The employer owns and controls the workplace and is statutorily obligated to maintain the minimally reasonable level of safety described in the regulations."

Employers should take steps before an accident occurs in the workplace to ensure that a defence of due diligence is available to them. These steps include the following:
1. Implement a plan to identify all possible workplace hazards and carry out corrective action to prevent the likelihood of such hazards causing accidents in the future. A comprehensive workplace safety audit should be conducted in which the policies and procedures governing the safe operation of all equipment and machinery are considered and reduced to writing.   
2. Ensure that written occupational health and safety policies, practices and procedures are in place. This will provide documentary evidence that can be used in court to demonstrate that the employer has carried out workplace safety audits, identified potentially hazardous conditions and practices, and made changes to correct these.   
3. Ensure that appropriate training has been provided to all employees. Specifically, the employer's policies, practices and procedures must be communicated to employees. A record of the dates and manner of training and education programs should be kept. In addition, employees should sign an acknowledgement that they have read and been provided with a copy of all policies and procedures.
4. Implement a program for the monitoring of the workplace to ensure compliance by employees with all health and safety policies, practices and procedures. Supervisors should be asked to perform unannounced spot checks and/or to complete regular compliance review reports in which any breaches of policies, practices and procedures are noted. Records should be kept so that the employer can establish in court that it has made ongoing efforts to ensure that such policies, practices and procedures are being complied with. Similarly, records relating to the disciplining of employees who have violated policies, practices and procedures should be kept.
5. Establish a documented procedure for accident reporting and investigation. Employees should be encouraged to report "close calls"  so that the circumstances of such events can be investigated. This information is critical in both revising and improving existing policies, practices and procedures, and in establishing in court that the employer has been acting with due diligence.

It is the employer's actions before - and not after - an accident or injury occurs in the workplace that are the key to successfully relying on the defence of due diligence in court.