Department of Transportation rules taking effect Jan. 1 require employers to periodically test heavy-duty truck divers and others for both alcohol and drug use.

Employers with 50 or more drivers need a plan in place at the start of the year. Employers with fewer than 50 drivers much comply by Jan. 1, 1996.

The regulations apply to highway vehicles weighing more than 26,000 pounds; vehicles designed to carry 16 or more passengers; or ones used to transport hazardous materials.

Dr. David J. Fletcher of Midwest Occupational Health Associates said about 6,000 Decatur-area residents will be affected by the rules.

About 120 people attended a drug- and alcohol-testing seminar Tuesday at the Holiday Inn, presented by MOHA and RocheCompuChem Laboratories.

Speakers included Dr. Paula Childs, a Roche vice president who helped the Department of Health and Human Services devise employee drug-testing standards; Car E. Johnson, a specialist in labor law who said he has been heavily involved in drug-testing issues since 1986; Dr. Dennis Rademacher, medical director of St. Mary's Hospital's treatment center, and Fletcher, whose firm specializes in industrial medicine and regulatory compliance.

Johnson, an associate in the Chicago law firm Seyfarth, Shaw, Fairweather & Geraldson, advised employers to bargain with unions over the details of substance abuse programs.

"Employers maximize outcomes when they invite union participation," Johnson said.

While employers may be bound by federal rules, those rules fail to address details such as who pays for treatment programs and whether employees may be dismissed for failing drug tests.

Johnson noted state laws in Illinois and elsewhere prohibit discrimination against employees for use of legal substances, such as alcohol and tobacco, and said there will be more community concern for employees who are dismissed over alcohol use than over illegal drug use.

Johnson also advised employers to contract with independent physicians for drug testing and evaluation services to insulate themselves from privileged and confidential information that discharged employees could use against them.