There are several hundred radio‐frequency (RF) heaters in industrial use in Finland. No exposure or performance standards have been established for this kind of device in our country. This paper describes measurements of strength of electric and magnetic fields near 35 plastic‐welding machines, all operating at 27 MHz at nominal power outputs that range from 0.5 to 35 kW. Approximately 70% of the heaters radiated RF energy at strengths that exceeded common standards (200 V m−1, 0.5 A m−1). The Finnish proposed safety standard (60 V m−1, 0.2 A m−1) was exceeded in 80% of the cases. The results indicate that both electric and magnetic fields should be measured in