DENVER -- An ozone alert for the Denver metro area was continued through Friday, for the fourth straight day. The alert also included Ft. Collins, Greeley, and Colorado Springs.

"Ozone was expected to climb into the moderate to unhealthy-for-sensitive groups range in many areas this afternoon and evening," the alert stated. "Unusually sensitive people should limit prolonged outdoor exertion between 2 p.m. and 11 p.m."

It was the 12th ozone alert issued for the area this summer. The ozone contributes to smog during hot, dry summer days.

High ozone levels can trigger asthma attacks and breathing difficulties for people with pre-existing respiratory ailments. Even people who exercise out-of-doors may experience breathing difficulties, eye irritation, and reduced resistance to lung infections and colds if they are exposed to high ozone levels over a prolonged period..

Experts at the Colorado Department of Public Health and Environment predicted that ozone levels could stay high for the remainder of the week because the forecast called for the hot weather pattern to continue.

Health officials urged residents to take precautions to help limit the amount of ozone that is contributed to the atmosphere and issued the following tips:

At Home:

Tightly cap all solvents (paint thinners and strippers, degreasers, and some cleaning products). Solvents contain pollution-causing vapors.
Postpone painting, stripping and refinishing projects to avoid the morning and mid-day summertime heat. Better yet, wait until the fall or spring.
Use water-based products (paints, stains and sealants).

In the Yard:

Delay mowing your lawn to another day. Don't mow, let it grow!
Avoid using high-emitting, gasoline-powered yard equipment. Electric alternatives are an efficient, environmentally-friendly alternative.
Use an electric starter or a "charcoal chimney" to start your barbeque grill. Lighter fluid contains a lot of harmful vapors that escape into our air and contribute to summertime air pollution.

On the Go:

Stop at the click when refueling your car. Overfilling your tank often results in fuel spills and always allows unnecessary pollution-causing vapors to escape into our air.
Refuel in the evenings after dusk. By refueling after the sun goes down, fuel vapors do not have as much of a chance to "cook" in the mid-day sun and become harmful ground-level ozone.
Maintain your vehicle. A poorly-maintained vehicle can pollute as much as 25 times more than a well-maintained one.