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What Do You Need to Prove in a Defective Product Case?

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Chuck Geerhart
What to Prove in Defective Product Case

Using products of all types is part of everyday life.

It’s rare to stop and consider whether the products are safe—that is until someone gets hurt. 

Compensation is available when a defective product causes an injury.

To receive compensation, proving a defective product caused the plaintiff’s injury is essential.

Types of Product Defect Claims

What is needed to prove a defective product caused injury in California depends on the type of product defect claim alleged.

Strict liability, breach of warranty, and negligence claims are common product claims. 

Strict Liability 

A party is often strictly liable for injuries caused by the product. California product liability law generally imposes liability without proving negligence.

Proving fault or intent is not required in a strict liability action. What matters is that the action occurred and the plaintiff sustained an injury.  

For most products, strict liability is available for three types of product defects:

  • Manufacturing defects,
  • Design defects, and 
  • Failure to warn. 

The proof required for each type of defect is different. In general, to prevail on a  strict product liability claim,  a plaintiff must prove four elements: 

  1. The defendant designed, manufactured, distributed, or sold the defective product.
  2. The product contained the defect when it left the defendant’s control.  
  3. The plaintiff used the product in a reasonably foreseeable manner. 
  4. The plaintiff suffered harm as a result of the defect.

“Reasonably foreseeable” requires the manufacturer to anticipate a consumer’s product use. For each defect type, a plaintiff must prove that the product is unreasonably dangerous. 

Manufacturing defects 

A manufacturing defect claim alleges a product deviated from the manufacturer’s typical units.

The deviation must render the product defective. The plaintiff must prove that the product deviated from the product’s design.

Design defect 

A design defect claim alleges that a product’s design caused the defective product.

The plaintiff must prove that the design caused the user’s injury. A plaintiff may prove a design defect in one of two ways. 

A plaintiff may prove a design defect claim under the consumer expectations test. A plaintiff may use this test if an ordinary everyday user could conclude that the product failed to perform as expected. 

Proving a defective product under California’s risk-benefit test is the other way. Under this test, a plaintiff must prove that:

  • The defendant manufactured, distributed, or sold the product;
  • The plaintiff was harmed; and
  • The product’s design was a proximate cause of the plaintiff’s injuries.

If the plaintiff establishes these elements, the burden shifts to the defendant. The defendant must prove that the benefits of the product’s design outweigh the risks. 

Failure to warn

A plaintiff must prove the defendant distributed or sold the product without sufficient warnings.

Plaintiffs use expert opinions to support the allegations of failure to warn. The plaintiff must prove that the defendant failed to adequately warn of a known risk.   

Breach of Warranty

When a product fails to fulfill the intended purpose, a plaintiff may claim a breach of warranty claim.

The purpose can be expressly stated or implied. Breach of warranty claims are governed by statute and apply to the sale of goods.

Breach of warning claims include:

A plaintiff cannot recover if the injury results from improper use of the product. 


Negligence claims in the product liability context include claims for negligent manufacture, design, and warning. A plaintiff must prove all elements of a general negligence case.

These elements include duty, breach, causation, and damages. The conduct of the manufacturer controls, not the condition of the product. 

Consult with a California Product Liability Lawyer 

If a product injures you in California, the Law Office of Chuck Geerhart can help. You should consult with a San Francisco product liability lawyer as soon as you are aware of your injury. 

You need a lawyer who will analyze the strengths and weaknesses of your particular case.

Handling only a small number of cases a year allows Mr. Geerhart to work closely with clients. He is able to use his over 30 years of experience to fight on your behalf.

Chuck Geerhart began his career working as a civil defense attorney. He knows the opponent’s strategies and will use that knowledge to your advantage.

Contact us online or call today to schedule a consultation.

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