By Todd Wels

Triplicate staff writer

U.S. Highway 199 was closed to traffic Thursday, after a pickup truck towing a fifth-wheel trailer slammed into a semi truck and burst into flames.

The accident occurred at about 3 p.m., approximately three miles outside Crescent City.

Both vehicles were attempting to negotiate a sharp curve when they collided head-on, caving in the front of the pickup truck and severely damaging the semis front axle.

Its definitely a turn where they jockeyed for position both ways, said Officer Joe Collins of the California Highway Patrol, who noted that it was not immediately apparent which vehicle was at fault in the accident.

The pickup truck came to rest midway down the semis trailer.

That was when the 100-gallon propane tank the Chevy pickup was carrying burst into flames.

It started with a little flame under the hood and we could not get the s.o.b. to go out, said a Crescent Fire Protection District firefighter who was called to the scene.

The fire gutted the cab of the pickup truck, sending flames twenty feet into the air and igniting the semis trailer.

CFPD personnel were joined by Fort Dick Fire Protection District personnel, as well as firefighters from the California Department of Forestry, when it became apparent that the fire would not be easily extinguished.

According to CFPD Chief Fred Cox, who was on the scene, a gas fire must be allowed to burn itself out at least until the gas pressure can be stopped via a shutoff valve. If the fire were to be extinguished without shutting off the valve, a temperature differential could form and cause an explosion.

With the amount of propane in question at the crash, Cox said that explosion could have had a radius of half a mile.

A large hole was burned into the fifth-wheel trailer towed by the pickup.

According to a spokesman for the Highway Patrol, the semi trailer was only slightly damaged by the fire, but structural integrity tests will still need to be performed before it can be moved from the roadside.

An elderly woman who rode in the pickup truck, whose name has not been released, was taken to Sutter Coast Hospital with a complaint of chest pains.

A man riding in the pickup had a bloody mouth, but declined medical treatment, Collins said.

According to the CHP, the road will be closed at least part of today while workers begin the process of removing the semi from the road.

A spokesman for the CHP said he was unsure how long the highway will remain closed.

A detour, utilizing U.S. Highway 197, is currently in effect.