Duty to warn: what manufacturers owe injured Canadians

Products do not have to be broken to hurt people. Sometimes, the only thing missing is the right warning, and in Canada, that gap alone can make a manufacturer liable.

In this article, we’ll discuss the duty to warn in product liability law, and its related concepts to help Canadian personal injury lawyers. This article can also be used by lawyers as an educational piece for their own clients.

What does the duty to warn require from manufacturers?

The duty to warn requires manufacturers to tell consumers about the dangers in their products that they know, or should have reasonably known about, but that the ordinary consumer would not be expected to recognise on their own.

The classic Lambert case on duty to warn

This principle is set out in Lambert v. Lastoplex Chemicals Co., [1972] SCR 569. Edison Howard Lambert, a mechanical engineer, bought two cans of Supremo W-200. This fast-drying lacquer sealer made by Lastoplex Chemicals to seal a parquet floor in Lambert’s basement.

While applying the sealer, vapours spread to an adjacent furnace room and ignited on a gas pilot light, causing an explosion that burned Lambert and destroyed his property.

The cans carried three labels, all warning of inflammability in general terms, however:

• none of them specifically warned against leaving pilot lights on in nearby spaces, and
• none explained how far and fast the vapours could spread

A competitor’s product, by contrast, explicitly listed “furnaces, all pilot lights, spark-producing switches” as hazards to eliminate before use.

What the duty to warn requires

In restoring the judgment at trial against Lastoplex Chemicals, the court described the duty to warn in plain terms:

“A general warning, as for example, that the product is inflammable, will not suffice where the likelihood of fire may be increased according to the surroundings in which it may reasonably be expected that the product will be used. The required explicitness of the warning will, of course, vary with the danger likely to be encountered in the ordinary use of the product.”

In short, the duty to warn requires:

• specificity, not just general caution language
• disclosure of the actual, foreseeable danger in context
• warnings scaled to the severity of the risk involved

Here’s a video which explains more about product liability and its different types under Canadian law:

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When does a general warning fail the standard of care?

A warning that technically mentions danger can still fall short of the standard of care if it does not tell the consumer what they actually need to know to stay safe. The question courts ask is whether the warning was sufficient to bring home the true nature and extent of the risk to a reasonable user.

When the duty to warn is discharged

In the Lambert case, Lastoplex argued that Lambert’s professional credentials as a mechanical engineer meant that he should have known better. However, the Supreme Court rejected this.

It said that the duty to warn is only discharged where a consumer has voluntarily assumed the specific risk in question; meaning, that they consciously understood and accepted it. In this case, Lambert never turned his mind to the pilot lights in the adjacent room as a hazard, and nothing on the label told him to.

What Lastoplex was trying to invoke was the sophisticated user defence. However, it only works when the consumer’s knowledge extends specifically to the precise danger the warning should have addressed. As such, general professional expertise does not substitute for that.

Rather, common law established the test, which looks at what the manufacturer ought to have known, based on all available information at the material time, including information it could have obtained through reasonable research, testing, and analysis, and information available in the industry more broadly.

Factors that affect whether a warning meets the standard of care include:

• the severity and foreseeability of the harm
• the gap between what the manufacturer knows and what the average consumer knows
• whether the warning identifies not just that harm is possible, but specifically how it is likely to occur
• the location, size, and clarity of the warning on the product itself

If you’re a litigant who wants to know more about product liability law, to which the duty to warn is a part of, watch this video:

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How does the learned intermediary doctrine limit liability?

Not all products reach consumers directly. In the case of prescription drugs, surgical implants, and other medical products, a manufacturer often sells to a physician or medical establishment, who then uses the product in treating a patient.

In these situations, Canadian courts have recognised that a manufacturer may satisfy its duty to warn by adequately warning the physician rather than the patient directly. This is the learned intermediary doctrine.

The Hollis case on learned intermediary doctrine

The learned intermediary doctrine was examined in Hollis v. Dow Corning Corp., [1995] 4 SCR 634. Susan Hollis underwent surgery in 1983 to receive silicone breast implants manufactured by Dow Corning Corporation. Her surgeon, Dr. John Robert Birch, did not warn her of any risk of post-surgical rupture.

By 1985, one implant had ruptured inside her body, yet the cause was never determined. She suffered years of complications, including pain, further surgeries, and a subcutaneous mastectomy in 1987.

In its decision, the court confirmed that the learned intermediary rule applied because the implants were sold only to physicians and were not directly available to the public. The manufacturer could therefore discharge its duty to the patient by warning the surgeon.

However, the rule comes with a condition: the intermediary must be genuinely “learned,” which means that the manufacturer must have actually and fully informed the physician of all known risks.

The gap between what they knew and what is told

As written by the court, “the manufacturer can only be said to have discharged its duty to the consumer when the intermediary’s knowledge approximates that of the manufacturer.”

In this case, Dow’s warnings to the medical community failed that test, because:

• the 1976 brochure warned only that “abnormal squeezing or trauma” could rupture the implant
• the 1979 product insert addressed rupture only in the surgical context
• neither warned of rupture from normal, everyday activities

By 1985, Dow’s updated insert acknowledged that rupture could result from “normal living experiences including routine and purposeful trauma as in vigorous exercise, athletics, and intimate physical contact.”

As such, the gap between what Dow knew and what it told physicians was significant enough to make the rule unavailable as a defence.

What happens when manufacturers ignore new risk information?

The duty to warn in product liability law is a continuing obligation and does not expire at the point of sale. Manufacturers must warn their consumers not only of the dangers known when a product enters the market, but of dangers they discover afterward.

In Hollis, Dow received field reports of unexplained post-operative ruptures in its Silastic implants over nearly a decade:

• 1975–1979: 20 reports of unexplained ruptures
• 1980–1983: 34 reports, bringing the total to 54 before Ms. Hollis’s surgery in October 1983
• by early 1985: 78 reports in total, which is the year Dow finally updated its warnings

Dow argued it was only obliged to warn once it had reached definitive conclusions about the cause of the ruptures. However, the court rejected this argument, as the duty to warn can be triggered by uncertainty, not just certainty. It noted that it was “precisely because the ruptures were ‘unexplained’ that Dow should have been concerned.”

Obligations of manufacturers under the duty to warn

The practical obligations this creates for manufacturers include:

• monitoring field and service reports on an ongoing basis
• keeping pace with scientific literature and industry developments
• updating product information when new risk data emerges, even before definitive conclusions are reached
• recalling products where a risk cannot be adequately addressed through a warning alone

For personal injury lawyers, this is where post-market surveillance records become an important area of discovery. The question is not only what the manufacturer warned about at the time of sale, but what it knew or should have known by the time the plaintiff was injured.

Duty to warn: the warning gap that never closes

The duty to warn is, at its heart, a correction for the information gap between those who make products and those who use them. Courts have consistently held that manufacturers cannot pass that gap on to consumers by staying quiet, using vague language, or waiting for conclusive proof before speaking up.

From the lacquer sealer that exploded in a Lastoplex customer’s basement to the breast implants that ruptured inside Hollis, the lesson is the same: a warning that does not actually warn is no warning at all, and Canadian law will not let silence stand in for disclosure.

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