If you have never caught a whiff of anhydrous ammonia, consider yourself lucky.

On a busy, bright May morning several years ago, with early season tillage in full swing, a tractor-drawn anhydrous rig pulled over on the road by our farm. From my safe distance I saw the farmer, holding a handkerchief to his nose and mouth, lurch frantically toward the round, white tank. Something was terribly wrong. The gas was leaking, and the farmer needed help.

A neighbor driving by had stopped and, running over to help close the tank valve, caught a strong dose of the gas. While the neighbor turned the valve (the valve had to be shut off!), the breathless operator stepped back from his rig and was doubled over, coughing and gasping for air.

I unwittingly rushed toward the truck and ran smack-dab, head-on into the invisible wall of noxious vapor. It stopped me in my tracks. It seemed as if I had been broadsided and the air knocked straight out of me. The air from my lungs had been sucked out, and it was physically impossible to breathe anything back in. I smelled a sharp, peppery scent and felt a burning sensation in my lungs as I backed off. By now all three of us, particularly the first farmer who had taken the biggest whiff, were gasping, coughing and gagging. Another passerby dashed into town, grabbed an oxygen mask, and returned to the scene, where gradually everyone regained their breath.

Advances in NH3 application technology during the past few years are lessening the likelihood that you ever will smell of this potentially lethal gas. Improvements in breakaway couplers, stronger toolbars, anti-lock hitches and even GPS-compatible monitors are helping to keep the volatile vapors under control.

"The trend is toward larger and faster running bars," says Tim Nix, fertilizer product marketing manager with DMI.

"There is more commercial application, with more experienced operators, and fewer farmers actually applying anhydrous." However, that means that more NH3 is being applied at night, which increases the potential for transportation problems on roadways between fields. For that reason, says Nix, DMIcontinues to improve warning light systems on all the equipment it manufactures.

Benefits and dangers. The term anhydrous means "without water." When its liquid form or gas contacts body tissue - eyes, skin or respiratory tract - it removes the water and causes dehydration, cell destruction, chemical burns and, in extreme cases, death.

A University of Nebraska Extension study on anhydrous ammonia safety explains what we discovered on that May morning: NH3 has a built-in safety factor in that you cannot stand to breathe it. You back off and get away from it. People who have sustained burns or eye damage from exposure to the chemical are those who have been caught by a sudden release, with nowhere to escape.

"Always use your head when you're using anhydrous ammonia," warns Robert Grisso, Nebraska extension engineer and coauthor of the report. "Anhydrous is one of the most beneficial chemicals on the farm and a cheap source of nitrogen, but it is extremely dangerous when released uncontrolled into the environment."

The ubiquitous white tanks rolling across fields on a spring or fall afternoon contain anhydrous in a liquid state and are strong enough to withstand 250 psi of pressure. As outside temperatures increase, the vapor temperature inside the tanks increases as well. At 60 degrees F, the internal tank pressure is 93 psi. At 100 degrees F, it rises to 200 psi. Released from the tank pressure, the volatile anhydrous expands and cools to its normal -28 degrees F temperature, which can freeze and burn exposed skin. One cu. ft. of liquid NH3 under pressure will produce 855 cu. ft. of gas when released, according to the Nebraska study.

Because of that volatility, small mistakes can lead to tragic results. Typical among those mistakes are the following:

* Filling the tanks beyond the recommended 85%,

* Knocking open the hose-end valve (hoses are the weakest link in the NH3 application system),

* Moving the applicator tank before filling hoses have been disconnected from the nurse tank,

* Venting the pressure-release valve while a person is in the line of discharge,

* Breaking or using deteriorated transfer hoses,

* Failing to bleed hose couplings before disconnecting them,

* Hose pressure buildup from plugged knives,

* The release of ammonia when those knives are unplugged,

* Overturning an applicator or nurse tank.

Precautions. It doesn't take much for a poisonous release to occur and, likewise, operator protection and precautions are simple. Operators should never wear contact lenses when working with the machinery and should wear a face shield or unvented goggles, loose-fitting rubber gloves with an extended cuff to prevent liquid from running down sleeves when arms are raised and a heavy-duty long-sleeved shirt. When working with bulk quantities of anhydrous, operators should keep two rain suits and gas masks with ammonia canister filters available for emergencies.

Basic precautions include working upwind of the machinery, knowing what is situated downwind, handling valves and hoses gingerly, and assuming that plugged applicator tubes contain pressurized NH3. Regulations require that any farm vehicle used for anhydrous application carry at least one 5-gal. safety water tank (refilled with fresh water daily). Safety specialists recommend carrying another 5-gal. supply of fresh water on the tractor and a 6- to 8-oz. water-filled plastic eyewash bottle in your shirt pocket. Finally, leave a message of your whereabouts when applying anhydrous; if you are late, others will suspect that you are in trouble.

First aid. A person who has breathed anhydrous ammonia should be placed in a reclined position with head and shoulders elevated and life support measures administered if needed. A victim should be irrigated with fresh water immediately; beware of any open water nearby that may have contracted NH3 and be aqua ammonia solution. If eyelids are affected, wash them thoroughly and continuously until medical care arrives. If skin is involved, flood the area continuously with water for at least 15 min. Likewise, if the nose, mouth or throat is affected, rinse continuously for 15 min. Keep victims warm, treat them for shock and get them to an emergency room as soon as possible. Persons who suffer from chronic lung diseases or have a hypersensitivity to ammonia should not be employed where they could be exposed to it.

Transport. Nurse tanks of 3,000 gal. or less are considered "implements of husbandry" when used exclusively for agricultural purposes and must have "anhydrous ammonia" printed in large green letters, along with a nonflammable gas placard, on both sides and each end of the tank. Applicator tanks must contain the same identification on the rear of the container.

Make sure the tank is hitched securely and tow only one tank at a time. Fully loaded nurse tanks must travel no faster than 30 mph and must display a "Slow Moving Vehicle" sign. State law requires two red reflectors visible to the rear on the extreme right and left of the trailer and a red light visible to the rear for nighttime transport. Before transport, the operator should double-check the security and tightness of the ACME screw located on the tank that holds the hose in place. A dangling hose, bouncing off the road, could damage connections and lead to big trouble.

You can never be too careful. Once you are engulfed in that invisible cloud, it's too late.