Rosa v. Taser International: Ninth Circuit Court Of Appeals Upholds The State Of The Art Defense – Finds Manufacturer Not Liable For Failure To Warn

by CMCP - California Minority Counsel Program

TASER International, Inc. (“TASER”) manufactured the Advanced Taser M26 (the “Stun Gun”), which is a weapon often used by police officers to subdue suspects.  The Stun Gun operates in two modes:  “probe mode,” in which two metal darts are shot into the target’s body; and “drive-stun mode,” in which two electrodes on the front of the Stun Gun are placed in direct contact with the target’s skin.  Under both modes of operation, a series of electric pulses are sent through the target each time the trigger is depressed.

On August 29, 2004, shortly after 11:00 p.m., the Del Rey Oaks police department was called regarding a “disturbed” man in the street yelling.  Approximately seven officers responded and found Michael Rosa behaving as if he was “either really high or crazy.”  After a brief pursuit, Rosa threatened the officers with a two-by-four so Officer Doza shot Rosa with the Stun Gun in “probe mode.”  However, Rosa fell and broke the leads, which ended the shock.  Officer Doza loaded a new cartridge, shot Rosa a second time with the Stun Gun in “probe mode” and depressed the trigger six or seven times in an attempt to control Rosa.  Rosa continued to struggle, therefore, Officer Borges deployed his Stun Gun in “probe mode” and depressed the trigger three times.  Rosa finally fell to the ground, but continued to resist.  Therefore, Officer Doza again used his Stun Gun, this time in “drive-stun mode.”  After the officers were able to get Rosa in handcuffs, Rosa stopped breathing.  Resuscitation attempts at the scene and during transport to the hospital were unsuccessful.  Rosa’s heart went into cardiac arrest and he was pronounced dead at 12:30 a.m.

An autopsy revealed high levels of methamphetamines in Rosa’s blood.  The cause of death was listed as “ventricular arrhythmia due to methamphetamines intoxication.”  Significantly, “Taser application and arrest by police” was listed as a contributing factor to his death.  Subsequently, Rosa’s death was linked to metabolic acidosis, which is a condition where lactic acid – the byproduct of physical exertion – accumulates more quickly than the body can dispose of it.  This causes the pH of the body to decrease, which makes sudden cardiac arrhythmia more likely.

The plaintiffs – Rosa’s parents and daughter – filed suit against TASER claiming that Rosa died because TASER provided inadequate warnings regarding the dangers of the Stun Gun.  The plaintiffs asserted that TASER should have warned police officers that repeated exposure to the Stun Gun carried the risk of causing fatal levels of metabolic acidosis.  They pursued failure to warn claims under both strict liability and negligence theories.  California’s strict liability law requires the manufacturer to warn of a particular risk if it is “known or knowable in light of the generally recognized and prevailing best scientific and medical knowledge available at the time of manufacture and distribution.”  Under the negligence theory, the manufacturer is required to warn of “facts which make the product likely to be dangerous for its intended use.”

On TASER’s motion for summary judgment, the district court ruled that the plaintiffs did not “establish a triable issue of fact that the risk of metabolic acidosis was known or knowable when the [Stun Gun] at issue was distributed or when Rosa died.”  It concluded that the scientific research cited by the plaintiffs did not address TASER’s products, was not publicly available and/or amounted to nothing more than unproven hypotheses.  As such, TASER was not liable under strict liability or negligence.

On appeal, the plaintiffs argued that the district court erred by construing TASER’s duty to warn too narrowly.  The plaintiffs claimed that “any riskthat was discoverable through modern technology, no matter how unsubstantiated, was knowable by TASER.”  Therefore, TASER should have warned about the risk of metabolic acidosis based on four peer reviewed articles.

The first article was a 1996 study of the impact of acidosis on the risk of ventricular fibrillation, a form of cardiac arrest.  However, the court determined that the study only demonstrates that the risk of ventricular fibrillation increases as blood pH decreases, but does not link its findings or acidosis to the use of Stun Guns.  The second article was a 1999 case study on the link between metabolic acidosis and deaths that occur while in police custody, commonly referred to as “sudden in-custody death syndrome.”  The court concluded that the 1999 study is incomplete because lactate levels – an indicator of acidosis – were obtained in only one of the five cases studied.  Also, none of the five cases involve Stun Guns.  Consequently, the court found that the 1996 and 1999 studies did not put TASER on notice that the Stun Gun could cause metabolic acidosis.

The plaintiffs also relied on a 1999 study performed on behalf of the Department of Defense (“DOD”), which was published after Rosa’s death, and a 2001 article entitled Effects of Stun Guns and Tasers.  The Court found that the DOD study merely states that “deaths following Taser use may be due to acidosis,” but does not establish a causal link.  Further, the court ruled that the DOD study could not constitute generally accepted medical knowledge because it was not publicly available until after Rosa’s death.  The 2001 article was considered the “missing link” between Stun Guns, metabolic acidosis and cardiac arrest because it hypothesized that Stun Guns may contribute to sudden in-custody deaths by affecting the acid-base balance of the target.  However, the court pointed out that there was no attempt to test the hypothesis and, therefore, there was not adequate information to link the in-custody deaths to Stun Guns.  The Court concluded that this “sort of hypothetical side effect” is not sufficient to require a warning under California law.

As such, the Court of Appeal disagreed with the plaintiff’s overly broad interpretation of the scope of a manufacturer’s duty to warn.  The court confirmed that a manufacturer is not under a duty to warn of every report of a possible risk because “inundating the public with notice of any and every hint of danger” would dilute the force of any specific warning given.  Consequently, the knowledge of a potential side effect based on a single isolated report of a purely speculative link between a product and an injury may not require a warning.  Indeed, a manufacture is under a duty to warn of a particular risk only if the available scientific and medical knowledge makes it “known or knowable” when the product is manufactured or distributed.  As such, the plaintiff must show that the defendant could and/or should have known of the risk by establishing a causal link between the product and the risk by producing generally accepted scientific evidence, not just conjecture and speculation.

In conclusion, the court upheld the state of the art defense and refused to extend manufacturers’ duty to warn to include any and all potential risks associated with a product.  Although the plaintiffs’ relied on peer reviewed articles to support the claim that the risk of metabolic acidosis was “known or knowable,” the literature did not present a triable issue with respect to notice because it consisted of an untested hypothesis and failed to establish a causal link between Stun Guns and metabolic acidosis.  Because the risk was not proven through testing, it was merely an interesting theory and not the level of scientific evidence necessary to put TASER on notice.

Product liability defendants can rely on this decision when challenging failure to warn claims based on the state of the art defense.  In particular, in cases where the plaintiff relies on peer reviewed articles and studies, the evidence should be challenged based on whether it was publicly available at the time the product at issue was manufactured or distributed and, more importantly, whether it establishes a causal link between the product and the risk at issue.  Even if the evidence purports to establish a causal link between the product and the injury, the Rosadecision concludes that it must consist of proven and tested theories.  As pointed out by the Court of Appeals, untested hypotheses are nothing more than speculation and conjecture and, therefore, do not give rise to a duty to warn.

Dwayne Anderson is a Senior Associate at Morris Polich & Purdy LLP; 213-417-5180


Written by:

CMCP - California Minority Counsel Program

CMCP - California Minority Counsel Program on:

Readers' Choice 2017
Reporters on Deadline

"My best business intelligence, in one easy email…"

Your first step to building a free, personalized, morning email brief covering pertinent authors and topics on JD Supra:
Sign up using*

Already signed up? Log in here

*By using the service, you signify your acceptance of JD Supra's Privacy Policy.
Custom Email Digest
Privacy Policy (Updated: October 8, 2015):

JD Supra provides users with access to its legal industry publishing services (the "Service") through its website (the "Website") as well as through other sources. Our policies with regard to data collection and use of personal information of users of the Service, regardless of the manner in which users access the Service, and visitors to the Website are set forth in this statement ("Policy"). By using the Service, you signify your acceptance of this Policy.

Information Collection and Use by JD Supra

JD Supra collects users' names, companies, titles, e-mail address and industry. JD Supra also tracks the pages that users visit, logs IP addresses and aggregates non-personally identifiable user data and browser type. This data is gathered using cookies and other technologies.

The information and data collected is used to authenticate users and to send notifications relating to the Service, including email alerts to which users have subscribed; to manage the Service and Website, to improve the Service and to customize the user's experience. This information is also provided to the authors of the content to give them insight into their readership and help them to improve their content, so that it is most useful for our users.

JD Supra does not sell, rent or otherwise provide your details to third parties, other than to the authors of the content on JD Supra.

If you prefer not to enable cookies, you may change your browser settings to disable cookies; however, please note that rejecting cookies while visiting the Website may result in certain parts of the Website not operating correctly or as efficiently as if cookies were allowed.

Email Choice/Opt-out

Users who opt in to receive emails may choose to no longer receive e-mail updates and newsletters by selecting the "opt-out of future email" option in the email they receive from JD Supra or in their JD Supra account management screen.


JD Supra takes reasonable precautions to insure that user information is kept private. We restrict access to user information to those individuals who reasonably need access to perform their job functions, such as our third party email service, customer service personnel and technical staff. However, please note that no method of transmitting or storing data is completely secure and we cannot guarantee the security of user information. Unauthorized entry or use, hardware or software failure, and other factors may compromise the security of user information at any time.

If you have reason to believe that your interaction with us is no longer secure, you must immediately notify us of the problem by contacting us at In the unlikely event that we believe that the security of your user information in our possession or control may have been compromised, we may seek to notify you of that development and, if so, will endeavor to do so as promptly as practicable under the circumstances.

Sharing and Disclosure of Information JD Supra Collects

Except as otherwise described in this privacy statement, JD Supra will not disclose personal information to any third party unless we believe that disclosure is necessary to: (1) comply with applicable laws; (2) respond to governmental inquiries or requests; (3) comply with valid legal process; (4) protect the rights, privacy, safety or property of JD Supra, users of the Service, Website visitors or the public; (5) permit us to pursue available remedies or limit the damages that we may sustain; and (6) enforce our Terms & Conditions of Use.

In the event there is a change in the corporate structure of JD Supra such as, but not limited to, merger, consolidation, sale, liquidation or transfer of substantial assets, JD Supra may, in its sole discretion, transfer, sell or assign information collected on and through the Service to one or more affiliated or unaffiliated third parties.

Links to Other Websites

This Website and the Service may contain links to other websites. The operator of such other websites may collect information about you, including through cookies or other technologies. If you are using the Service through the Website and link to another site, you will leave the Website and this Policy will not apply to your use of and activity on those other sites. We encourage you to read the legal notices posted on those sites, including their privacy policies. We shall have no responsibility or liability for your visitation to, and the data collection and use practices of, such other sites. This Policy applies solely to the information collected in connection with your use of this Website and does not apply to any practices conducted offline or in connection with any other websites.

Changes in Our Privacy Policy

We reserve the right to change this Policy at any time. Please refer to the date at the top of this page to determine when this Policy was last revised. Any changes to our privacy policy will become effective upon posting of the revised policy on the Website. By continuing to use the Service or Website following such changes, you will be deemed to have agreed to such changes. If you do not agree with the terms of this Policy, as it may be amended from time to time, in whole or part, please do not continue using the Service or the Website.

Contacting JD Supra

If you have any questions about this privacy statement, the practices of this site, your dealings with this Web site, or if you would like to change any of the information you have provided to us, please contact us at:

- hide
*With LinkedIn, you don't need to create a separate login to manage your free JD Supra account, and we can make suggestions based on your needs and interests. We will not post anything on LinkedIn in your name. Or, sign up using your email address.