A Seller’s Duty to Warn of Dangerous Post-Sale Components

One of the most heated, cutting-edge issues in products liability and toxic torts law these days is the question of whether product manufacturers and sellers have a duty to warn end product users about the hazards associated with third-party components that will foreseeably be added to their products post-sale.

Products may be defective because they lack a warning about unreasonable and nonobvious dangers. The duty-to-warn aspect of products liability law requires that sellers, suppliers and manufacturers of products issue an adequate warning about all foreseeable risks.1 How do we get from the product seller’s duty to warn about unreasonable product dangers to its duty to warn about foreseeable post-sale modifications?

The general rule is that the seller has a defense when a product is substantially modified post-sale, and this modification brings about the dangerous feature.2 At comment h to Section 402A, however, the Restatement (Second) of Torts advises that, where the seller has reason to anticipate that a danger may result from a particular product use, it will have a duty to warn product users of that danger.3 Comment h warrants the rule that product sellers have a duty to warn of foreseeable modifications of their products likely to pose an unreasonable danger.

So, for instance, in Liriano v. Hobart Corporation, 4 the New York Court of Appeals explained that “in certain circumstances, a manufacturer may have a duty to warn of dangers associated with the use of its product even after it has been sold. Such a duty will generally arise where a defect or danger is revealed by user operation and brought to the attention of the manufacturer.”5

Moreover, in comment p to Section 2 of the Restatement (Third) of Torts: Products Liability, the reporters emphasize that:

[p]roduct misuse, modification, and alteration are forms of post-sale conduct by product users or others that can be relevant to the determination of the issues of defect, causation, or comparative responsibility. Whether such conduct affects one or more of the issues depends on the nature of the conduct and whether the manufacturer should have adopted a reasonable alternative design or provided a reasonable warning to protect against such conduct.6

The foreseeability exception to the substantial modification defense, articulated in comment h to Section 402A, provides one solid basis for liability in the dangerous post-sale component context. Reliance upon this principle should provide an important aspect of any motion or appellate practice in which the component part defense arises.


1 Basko v. Sterling Drug, Inc., 416 F.2d 417, 426 (2d Cir. 1969); Goehring v. Target, 91 Fed. Appx. 1, 5 (9th Cir., Jan. 16, 2004).


3 Id., at cmt. h.

4 92 N.Y.2d 232 (1998).

5 Id., at 239-41 (omitting citations).


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