Using sniffer dogs and forensic tests, international corporations are borrowing police tactics to weed drug-users out of the workforce.

Spreading from the sporting arena at the beginning of the decade, drug- testing was pioneered in the US where a third of the top 500 firms currently screen workers.

Imported here by the continental arms of multinational companies, screening has largely been confined to health-sensitive occupations like long-distance drivers, but evidence suggests the situation is shifting, with Irish firms following examples set in the US and UK where millions of workers routinely face testing.

Next year Aer Rianta will become one of the first Irish companies to blanket-test staff when it introduces urine testing as part of its recruitment process. Prospective employees, from cleaning women to floor managers, will be screened for evidence of cannabis, cocaine and heroin use. IBEC director Turlough O'Sullivan says: "More and more businesses are being affected by drugs, and we are increasingly consulted when an employer has to deal with a worker's poor performance which the company doctor has linked to drug use."

He says substance abuse, like alcoholism, is evident across the employment spectrum from manual workers to company executives and adds that employers should use thorough recruitment techniques by introducing a drug and alcohol test at the pre-employment stage.

How accurate are drug tests, and is a positive result necessarily evidence of a person's inability to do the job? The sporting world provides plenty of examples of innocent substances producing positive results, and similar scenarios have begun to crop up in job-screening. Recently a worker at London Underground was suspended after failing a random test, but it later turned out that the drug traces found had come from the poppy seeds on his lunchtime roll.

The consumption of cannabis produces chemicals which remain in the body for up to 30 days. So a joint smoked in Amsterdam, where the substance is legal, could lead to an individual being turned down for a job on their return home.

If traces of the drug linger in the body, its narcotic effect is limited to just a couple of hours, so why should employers worry about what workers get up to in their spare time?

According to Cathy Burke, press officer at Aer Rianta, the company believes drug consumption outside office hours has a negative effect in the workplace.

"Staff working in an airport environment deal with the public a lot, and if somebody is abusing a substance, that will impact on the organisation."

Mr O'Sullivan says it is up to individual IBEC members to decide on the best course of action to take once an employee or potential recruit has tested positive for cannabis. He adds, however, that there is much evidence to suggest people go on from hash to harder drugs.

In the US, corporations have taken screening further, using forensic techniques to delve into the past for evidence of drug use. By analysing a strand of hair from an employee, cannabis consumed three months previously can be detected.

Such zero-tolerance tactics have also gained a foothold in the UK. The oil industry recently paraded sniffer dogs on the floor of London's International Petroleum Exchange, firmly demonstrating its stance on drug-taking among employees.

Civil liberties groups in Britain argue that non-safety sensitive staff should be exempt from testing on the basis that what they get up to outside the office is none of their employers' business. Michael Finucane of the Irish Council for Civil Liberties maintains that employers planning to introduce tests have a responsibility to ensure they are scrupulously fair. "If somebody is refused a job on the basis of failing a test, they should be informed in writing and given the opportunity to contest."

Anti-drug campaigners believe that screening in the workplace acts as a powerful deterrent to narcotic abuse. Bernie McDonnell from Community Awareness of Drugs says the introduction of testing is a positive development.

"It helps support the information on the bad effects of drug-taking. Instead of simply telling children not to take drugs, parents can explain why by saying `You might go on to fail a medical test and lose your job'."