COLLIN COUNTY, Texas -- A strange odor is being investigated in Luca, Texas after two people were found unconscious inside a van early Wednesday evening.

A Collin County sheriff's deputy and four firefighters were called to check out the van, which belonged to a lawn care company, at about 4 p.m. Wednesday.

Two people inside the van, believed to be employees of the lawn care company, were pronounced dead. They have been identified as Ross Powell, 49, and Lyle Powell, 72. The medical examiner's office has determined that they died of accidental carbon monoxide toxicity.

When emergency crews opened the door, they were overcome by a strong smell of ammonia, officials said. They had skin irritation, chest pain, nausea, and a dry cough, and were sent to the hospital to be checked out. They have all since been released.

HazMat teams called to the scene found different chemicals inside the van. However, nothing was over the limit as far as being hazardous. No chemicals were labeled as ammonia, although that's how the smell is being described.

Officials say the ambulance and other equipment involved in the investigation will have to be de-contaminated due to the chemicals.

Residents nearby were told to shelter in place, but no one was evacuated.