Amazon-owned Zoox has grounded its autonomous vehicle test fleet in Atlanta after safety drivers were potentially exposed to toxic gases inside its vehicles in August, with as many as 40 workers possibly affected according to an Occupational Safety and Health Administration (OSHA) letter. The company discovered the exposures involved carbon monoxide, carbon dioxide, or hydrogen sulfide gas, leading to one worker filing an OSHA complaint and the agency opening an inquiry.

What Happened to Zoox's Atlanta Test Drivers?

The incidents began in early August when safety drivers started reporting exposure symptoms and strange smells in Zoox's modified Toyota Highlander SUVs. On August 14, the situation escalated when four workers training together in one vehicle became ill. One worker vomited, and others reported feeling lightheaded as they approached their morning break at a Chick-fil-A. After the workers called the dispatcher, Zoox arranged for them to be transported back to the depot via Uber.

What happened next raised additional concerns. Rather than allowing the workers to rest after reporting illness, Zoox put them back in a different test vehicle the same day. "They made us go right back in the field after we said we were throwing up," Jay Davis, one of the contractors who got sick, told TechCrunch. "I emailed HR, told her what's going on, and I told her I feel like it's messed up that y'all made us go [back out]." The second vehicle may have also contained toxic gases, as the workers experienced another bout of exposure symptoms later that day.

The illnesses continued through much of August until August 22, when someone called 911 for a sick worker. Following that incident, the Atlanta facility operated at limited capacity, with test vehicles quarantined while Zoox investigated. OSHA has since closed its inquiry.

Why Are Toxic Gases Building Up in Zoox's Test Vehicles?

Zoox's test fleet is unusual among major robotaxi developers because it uses internal combustion engine vehicles rather than electric ones. Waymo, Tesla, Avride, and Motional all use electric vehicles, which don't produce exhaust gases. This fundamental design choice makes Zoox's fleet vulnerable to carbon monoxide and carbon dioxide buildup, gases that naturally form when vehicles burn fuel.

These gases can enter a vehicle through exhaust system leaks or accumulate if a vehicle runs inside an enclosed space for extended periods. The National Highway Traffic Safety Administration (NHTSA) investigated Ford for six years over similar carbon monoxide buildup issues in its Explorer SUVs. In that case, the highest levels of carbon monoxide were found in police vehicles that had added sirens, lights, and other modifications, all of which can create sealing issues.

Zoox modifies its Highlanders by adding sensors and an autonomy computer for testing. The company also adds an interior "snorkel" above the central infotainment screen that pushes air toward rear-seat passengers. While Zoox stated it doesn't modify the ventilation systems, any changes to a vehicle can increase the risk that gases will leak into the cabin. The company does use an exhaust-capture system at its indoor depots, similar to what firehouses use to capture truck fumes, but this system may not have been sufficient to prevent the exposures.

What Did Zoox Tell OSHA About the Exposures?

In a September 10 letter to OSHA, Zoox identified 28 employees who rode in six test vehicles that had an "unexplained odor." The company said it examined the vehicles for signs of carbon dioxide and replaced their 12-volt batteries, since damaged batteries can produce hydrogen sulfide gas, which creates a "rotten egg" smell. Some employees reported noticing a similar smell in the cars.

Zoox told OSHA that 10 workers "voluntarily underwent medical evaluation" to determine whether any exposure had occurred. The company reported receiving only "one medical report identifying CO2 exposure." However, Davis and two other workers who became sick were told at the emergency room that their symptoms were consistent with carbon monoxide exposure, which is odorless and therefore harder to detect without specialized equipment.

Zoox

The company stated it hasn't identified the presence of carbon monoxide in its vehicles and consulted an outside medical expert to help investigate. Zoox said the only gas it detected in the impacted vehicles was CO2. In response, the company committed to adding CO2 monitors to the vehicles going forward.

How to Protect Workers in Autonomous Vehicle Testing Programs

• Implement Real-Time Gas Monitoring: Install carbon monoxide, carbon dioxide, and hydrogen sulfide detectors in all test vehicles, with alerts that notify drivers and dispatchers immediately if dangerous levels are detected.
• Establish Clear Health Protocols: Create mandatory rest and medical evaluation procedures when workers report exposure symptoms, rather than reassigning them to different vehicles on the same day.
• Conduct Regular Maintenance Inspections: Perform routine exhaust system leak tests and battery inspections on all modified test vehicles, with documented results shared with safety teams.
• Prioritize Electric Test Fleets: Transition to electric vehicles for autonomous testing programs to eliminate exhaust gas exposure risks entirely, as competitors like Waymo and Tesla have already done.
• Improve Ventilation Systems: Upgrade cabin air filtration and ventilation in modified vehicles, and avoid modifications that could compromise the vehicle's original sealing integrity.

This incident highlights a broader tension in the robotaxi industry. Zoox is expanding rapidly into new cities and scaling operations in Las Vegas and San Francisco to compete with market leader Waymo. However, this growth has come with safety challenges for test drivers. TechCrunch previously reported that contractors have sustained injuries from sudden braking and swerving in Zoox test vehicles. Waymo has also reported similar test driver injuries to OSHA, suggesting that rapid expansion in autonomous vehicle testing may be outpacing safety infrastructure across the industry.

The grounding of Zoox's Atlanta fleet represents a significant setback for the company's expansion plans. While Zoox's purpose-built robotaxis, which are all electric, are not affected by the toxic gas issue, the incident underscores the risks associated with using modified internal combustion engine vehicles for testing autonomous driving systems. As the robotaxi industry races to scale operations, worker safety in testing programs remains a critical challenge that companies must address before expanding to new markets.