Drivers see them every day on the highway: tanker trucks roaring along, their sides and rear decorated with diamond-shaped placards reading FLAMMABLE and bearing cryptic numbers.

The number is a code representing the types of hazardous material carried. It will assist the emergency response teams that will rush to the scene if that truck ahead were to overturn, explode or leak.Depend on it, the hazardous cargoes shipped along Utah's highways are not simply accidents waiting to happen - many accidents have already taken place and more are inevitable.

Yet nobody knows how much acid, gasoline, rocket fuel, solvents and other dangerous chemicals go through - not the federal government, not the state government nor trucking association. And except for explosives and radioactive material, no regulations prevent the most toxic chemicals from barreling through your neighborhood.

Why should you care? Well, here are just a couple of examples:

-Last week, a diesel fuel tanker truck carrying 7,400 gallons hit a rock and plunged into a ravine just south of the Utah-Arizona border. The accident closed I-15 for nearly seven hours.

The driver was killed and the truck split apart. Poisonous fuel poured into a gully emptying into the Virgin River, which is a water supply and an important wildlife habitat. Fortunately, hazardous materials teams from Utah and Arizona managed to catch it before it reached the river.

- On July 28, 1988, about 240 gallons of sodium cyanide in pellet form spilled from a truck on I-15 about 20 miles south of Fillmore, forcing closure of a 60-mile stretch of one of Utah's busiest roads, from Scipio to Cove Fort. Shortly after the spill, another trucker drove through the mess. He was hospitalized briefly when he arrived in Salt Lake City, complaining of headaches.

Also suffering minor cyanide poisoning were a Utah Highway Patrol trooper and the driver of the truck in the accident, which was headed from California to Green River, Wyo.

Meanwhile, cleanup crews from the Woods Cross-based company, Hatchco, raced to remove the pellets from a three-quarter-mile stretch of highway. They had to get them out before rain fell, releasing deadly cyanide gas. The freeway was closed for most of four days. The cleanup cost $100,000.

"It could have got out of hand," said Dave Alder, transportation safety programs coordinator for the Utah Department of Transportation. "It could have been a lot more serious."

If the spill had happened in downtown Salt Lake City, he said, many cars would have driven through the mess before crews could have stopped traffic.

Nobody knows how many accidents involving hazardous material happen in the state. That sort of information "isn't even collected right now," Alder said.

Norman Lindgren, director of UDOT's Office of Motor Carrier Safety, would not guess how much hazardous material is hauled on Utah's highways. "It'd be very difficult, because we don't keep track of it," he said.

But in 1987, a total of 1,617 truck accidents were reported, among the 9,000 motor carrier companies operating in Utah.

Lindgren said about 13 percent to 14 percent of all trucks carry hazardous material exclusively. That amounts to many thousands of shipments per year.

Count the vehicles that only sometimes carry it, like the grocery delivery semitrailer truck that may haul cartons of Draino along with its other goods, and the figure shoots up. Around 40 percent of all trucks sometimes carry hazardous cargo.

Do these vehicles need special permits? "Not in the state of Utah," he said.

The shipments will undoubtedly continue to increase. A hazardous-waste landfill in Tooele County handles 50 to 60 loads per day of hazardous material, according to UDOT.

A hazardous-waste incinerator is to be built by the Aptus company in Tooele County, with construction starting this spring.

The Bureau of Land Management has begun to write an environmental impact statement on a second incinerator, to be built seven miles west of the Aptus facility. It would store, transfer and treat 130,000 tons of wastes annually.

According to Lindgren, a lot of fuel is shipped around "because of the refineries we have here." Much of the traffic is crude oil trucked from fields in the Uintah Basin to refineries in North Salt Lake.

The oil is refined into gasoline. "There's lot of gasoline in the (Salt Lake) Valley _ a tremendous amount," he said.

He said that in 1988, the Utah Highway Patrol investigated about 50 incidents involving leaking cargo, gasoline or oil tanks.

Wayne Goudie, the officer in charge of the federal government's Office of Motor Carriers in Salt Lake City, estimates that 10 percent of trucks carry hazardous material. "But I'm not sure there's any source that can pinpoint how many tons that have been shipped."

Goudie said Salt Lake City once considered restricting hazardous material to certain routes. The idea wasn't implemented.

UDOT is working to "establish a system where we can monitor the trucks going through the state," he said. "But at the present time, there is not a permit system."

The exception applies to trucks hauling explosives or nuclear material. Utah adopted federal regulations that require them to avoid highly populated areas.

Haulers of radioactive material or explosives must carry a written route plan and take the least-congested route available to them.

"Downtown Salt Lake City would not be an acceptable route," said another UDOT spokesman, "unless there is a use in downtown Salt Lake City for that product."

As far as other types of hazardous material are concerned, from gasoline to acid, "there is no established route plan for them," he added.

The regulations say truckers should plan their routes and take the least-congested one available. It's up to the trucker's discretion, although he may be questioned about why he was in a congested area if he is involved in an accident there.

"What goes through Utah?" said Alder. "Everything. It's that easy. We're a bridge state."

Most hazardous materials accidents in this state involve petroleum tankers. Because the gasoline is liquid, it tends to slosh around inside, causing instability that can lead to rollovers.

"Generally tankers don't blow up. They just burn. There's not that much pressure in them," Alder said. "We had two twin tankers burn right to the ground up by Mountain Dell (Reservoir) a few years back. That's all it was _ a nice big fire."

Naturally, some residents want hazardous material kept out of cities.

"Well, you keep all hazardous material out of a city and there's no city, because it thrives on hazardous materials. You'd end up with no hardware stores, no hospitals, no gas stations," Alder said.

LeRoy Ownbey, presently with Ryder Truck Rental in Salt Lake City and a former employee of the Utah Motor Transport Association, concurs.

"As far as ordinary hazardous-material loads, it's difficult to do that because a lot of them are consumer materials," he said.

For example, what do you do about the gasoline truck making a delivery to the 7-Eleven store across from East High School?

"Hair spray and ballpoint pens, all this sort of thing are hazardous in a way," said the association's Reed L. Reeve. "Hazardous material and hazardous waste is a byproduct of industry. Every state and most manufacturing businesses are producers of it, even the state of Utah.

"We've got to recognize we cannot restrict industry by saying we can't have any hazardous materials around."

UDOT's Lindgren said state officials are designing a new requirement that will force carriers that operate in the state to obtain a permit. It is scheduled to go into effect later this year. Whether a permit is granted will depend on the company's record in other states as well as here.

Also in April, UDOT will inaugurate a new computerized system to keep track of truck accidents, listing the types of mishaps and kinds of material hauled. The accident ratios may help officials to zero in on especially dangerous operations.

Meanwhile, the department conducts safety audits on trucks. About 10 percent fail the test and the owners must bring the vehicles into compliance.

"We do safety inspections throughout the state," Lindgren said. But the department has only 13 safety auditors, so it can't look at each truck every year.

Highway Patrol troopers trained at spotting unsafe rigs may pull over a vehicle on the freeway, or at a port of entry, and do an immediate inspection. If a serious problem is discovered, "they put him right out of service."

Utah is building a new system of entry ports. The first is to be completed this year on I-15 near St. George, to be operated jointly with Arizona. Other "superports" will be built on I-70 near Green River and I-80 near Wendover. A port on I-15 near Brigham City will be rebuilt.4 The program will take five years to complete.

"Each of the new ports will have inspection bays for the purpose of doing safety inspections on trucks," he said. "They'll have enclosed inspection bays so they can do it in all types of weather, 24 hours."

Truck accident rates have been dropping in Utah. Still, disasters with hazardous cargo are reported throughout the country.

"I don't think there's any question of it, that someday it'll happen," Lindgren said.

"Some of these things are extremely dangerous," said the federal government's Goudie. "High explosives, flammable gases are fairly commonly shipped."

Regulations require that shipping papers be carried in the truck, identifying the material hauled in case of an emergency. The most dangerous material, called "Poison A" or "high explosives," must be identified in placards posted on the truck's four sides.

Also, the Utah Bureau of Solid and Hazardous Waste has a staff of 65, including a 12-member compliance staff. The bureau gets involved with the shipment of hazardous waste, and the cleanup of any hazardous material that spills. Once it's on the ground, it's waste.

Spills of toxic chemicals are fairly rare, "maybe one or two a year," said Dennis Downs, assistant bureau director.