JOINT 

NID!iH / El5HR • 

RADIOFREQUENCY (RF) 

SEALERS AND HEATERS: 

POTENTIAL HEAL TH HAZARDS 

AND THEIR PREVENTION 

December 4, 1979 

WARNING 

RADIOFREOUENCY HAZARD RADIATION 

U.S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE 

Public Health Service 

Center tor Disease Control 

National Institute tor Occupational Safety and Health 

U.S.DEPARTMENT OF LABOR 

Occupational Safety and Health Administration 

' 

This Current Intelligence Bulletin is a joint effort of the National Institute for 

Occupational Safety and Health (NIOSH) and the Occupational Safety and Health 

Administration (OSHA), and is a product of the NIOSH Current Intelligence System. 

The staff of the NIOSH Technical Evaluation and Review Branch, Office of 

Extramural Coordination and Special Projects, was responsible for the preparation 

of the Bulletin. Major contributions to the content of the Bulletin were made by 

NIOSH Division of Criteria Documentation and Standards Development and 

Division of Biomedical and Behavioral Science and by staff of the Occupation:i.l 

Safety and Health Administration. 

The purpose of the NIOSH Current Intelligence System is to promptly review, 

evaluate, and supplement new information received by NIOSH on occupational 

hazards that are either unrecognized or are greater than generally known. As 

warranted by its evaluation, the information is capsulized and disseminated to 

NIOSH staff, other government agencies, and the occupational health community, 

including labor, industry, academia, and public interest groups. With respect to 

currently known hazard information this system also serves to advise appropriate 

members of the above groups of recently acquired specific knowledge which may 

have an impact on their programs or perception of the hazard. Above all, the 

Current Intelligence System is designed to protect the health of American workers 

and to allow them to work in the safest possible environment. 

"Employers in every state who want help in recognizing and 

correcting safety and health hazards in their workplaces can 

get it from a free onsite consultation service funded by the 

Occupational Safety and Health Administration. The 

service is delivered by state governments or private sector 

contractors using well trained professional staff. Employers 

can obtain from OSHA the name, address, and phone 

numbers of the state agency or contractor that provides this 

service." 

FURTHER INFORMATION: 

Chief, 

Physical Agents Effects Branch 

Division of Biomedical and 

Director 

Directorate of Technical Support 

Behavioral Science Occupational Safety and Health 

National Institute for Occupational 

Safety and Health 

Administration 

200 Constitution Avenue, N.W. 

4676 Columbia Parkway Washington, D.C. 20210 

Cincinnati, Ohio 45226 

(513) 684-8483 

(202) 523-7031 

Mention of company name or product does 

not constitute endorsement by the National 

Institute for Occupational Safety and 

Health or the Occupational Safety and 

Health Administration. 

JOINT NIOSH/OSH A 

CURRENT INTELLIGENCE BULLETIN: #33 

Radiofrequency (RF) Sealers and Heaters: 

Potential Health Hazards and Their Prevention 

December 4, 1979 

The National Institute for Occupational Safety and Health (NIOSH) and the 

Occupational Safety and Health Administration (OSHA) are concerned about 

potential health hazards to workers exposed to radiofrequency (RF) energy emitted 

from RF dielectric heaters (more widely known as RF sealers and heaters). RF 

energy is nonionizing electromagnetic radiation and should not be confused with 

X-rays and other ionizing radiation. RF energy, when absorbed in sufficient 

amounts by workers, may produce adverse thermal effects resulting from heating 

of deep body tissue which may include potentially damaging alterations in cells. 

Absorption of RF energy may also result in "nonthermal" effects on cells or tissue, 

which may occur without a measureable increase in tissue or body temperature. 

"Nonthermal" effects have been reported to occur at exposure levels lower than 

those that cause thermal effects. While scientists are not in complete agreement 

regarding the significance of reports of "nonthermal" effects observed in laboratory animals, NIOSH believes there is sufficient evidence of such effects to cause 

concern about human exposures. NIOSH and OSHA recommend that precautionary 

measures be instituted to minimize the risk to workers from unwarranted exposure 

to RF energy. Section V of the Appendix to this Bulletin lists engineering controls, 

such as shielding, and other immediate actions that should be taken. Also, NIOSH 

and OSHA are issuing this Bulletin to alert employers and workers to the potential 

for overexposure of workers to RF energy from RF sealers and heaters, and to 

recommend control technology that can prevent unwarranted exposures. 

Workers near RF sealers may be unaware of their exposure to RF emissions, 

because the RF energy from sealers and heaters can penetrate deeply into the body 

without activating the heat sensors located in the skin. A false sense of employee 

safety may exist; in many inst ances, worker exposur es to RF energy may not have 

been properly assessed. This has been due, largely, to the complex problems of 

measurement and thus the misapplication of the instruments available for 

monitoring RF energy levels. Recently, monitoring instruments that facilitate 

accurate measurement of worker exposure have been developed. Federal survey 

teams, equipped with these new instruments, have detected excessive exposures of 

workers to RF energy. 

NIOSH is seeking additional information about the adverse effects of RF energy 

and effective control t echnology. The Institute would appreciate receiving 

information concerning adverse health effects among workers which might be 

associated with their exposure to RF energy in the workplace and information on 

methods for retrofitting existing RF sealers and heaters in order to control the 

1 
emission of RF energy. NIOSH and OSHA request that manufacturers, distributors, 

and users of RF sealers and heaters transmit the information in this Bulletin to 

their customers and employees, and that professional societies, trade associations, 

and unions inform their members. 

BACKGROUND 

RF sealers have been used for more than 30 years, but there are no reliable, 

documented estimates of the number of units in present use or of the number of 

workers operating RF sealers. However, it is generally believed that the number of 

RF sealers and heaters in use is approximately 20,000 and that there are about 

30,000 to 40,000 workers operating these units. A list of companies believed to 

manufacture RF sealers and/or heaters appears in Section I of the attached 

Appendix. 

RF sealers are used to heat, melt, or cure materials such as plastic, rubber, or 

glue. Specific uses include: 1) the manufacture of many plastic products such as 

toys, vinyl loose-leaf binders, rain apparel, waterproof containers, furniture slip 

covers, and packaging materials; 2) wood lamination and veneer processes, 

including glue setting; 3) embossing and drying operations in the textile, paper, 

plastic, and leather industries; and 4) curing of various materials including 

plasticized polyvinyl chloride, wood resins, polyurethane foam, concrete binder 

materials, rubber tires, and epoxy resins. An extensive list of occupations 

involving the use of RF sealers and heaters is presented in Section II of the 

attached Appendix. 

Experiments in animals suggest that the potential consequences of absorbing 

excessive amounts of RF energy may include changes in: the eye, the central 

nervous system, conditioned reflex behavior, heart rate, chemical composition of 

the blood, and the immunologic system. Effects on reproduction and on the 

development of offspring of females exposed during pregnancy have also been 

reported. 

As previously mentioned, a false sense of employee safety may exist in many 

industrial settings because worker exposures to RF energy may not have been 

properly assessed. The recent development of monitoring instruments that 

facilitate accurate measurement of worker exposure to RF energy allowed for a 

series of studies at workplaces where RF sealers and heaters are used. The results 

of a NIOSH study indicate that the majority of the workers surveyed were exposed 

to RF energy at levels exceeding values citable by OSHA. 1 RF energy in the 

immediate area of a worker has been measured at levels as great as ten times the 

values citable by OSHA. 1 '

2 A list of manufacturers of instruments suitable for 

measurement of RF energy is presented in Section ill of the attached Appendix. 

This Bulletin will provide an overview of the potential adverse health effects 

associated with the use of RF dielectric heaters. The Appendix contains technical 

information to assist research, engineering, and manufacturing personnel in evaluating this potential hazard and for initiating appropriate modification and controls 

to prevent unwarranted worker exposure. 

2 
BIOLOGICAL EFFECTS OF RF ENERGY 

Excess amounts of RF energy absorbed by workers may produce adverse thermal 

effects resulting from heating of deep bo.dy tissue. These thermal effects may 

include potentially damaging alterations in cells caused by localized increases in 

tissue temperature. Scientists involved in this work have generally agreed that 

exposures of humans to levels of RF energy at or above a far-field power density of 

10 mW /cm2 (see Section IV.C of the attached Appendix) can cause net increases in 

tissue or body temperatures, and that exposures at or above these values should be 

avoided. 3 In the far field, a power density of 10 mWfcm2 is equivalent to a mean 

squared electric field strength of 40,000 volts 2 /meter or a mean squared magnetic 

field strength of 0.25 amperes

2 /meter 2 • Because the body's surface heat sensors, 

located in the skin, are not activated when RF energy is absorbed deep within body 

tissues, RF sealer workers may be unaware that they are absorbing RF energy. 

Absorption of RF energy may also r esult in "nonthermal" effects on cells or tissue, 

which may occur without a measurable increase in tissue or body temperature. 

"Nonthermal" effects are reported to occur from exposure to RF energy at field 

strengths lower than those necessary to cause thermal effects. i+,s While scientists 

are not in complete agreement regarding the significance of reports of 

"nonthermal" effects observed in laboratory animals, NIOSH believes there is 

sufficient documentation of such effects to cause concern. 

For radiation frequencies similar to those commonly used with RF sealers and 

heaters, reported observations at relatively low energy levels in laboratory rats or 

rabbits included changes in: electroencephalographic (EEG) recordings of 

electrical activity of the brain, 6 conditioned reflex behavior, 6 '

7 chemical composition of the blood, 6 the endocrine (hormonal) system, 6 '

8 and the immunologic 

(infection defense) system. 6 '

9 Details of these experiments are summarized in 

Section IV.E of the attached Appendix. For the frequencies at which these 

observations have been made the rates of energy absorption in man are much 

greater than in the laboratory animals. 10 Therefore, the biological effects 

observed in the laboratory animals may occur in humans at exposure levels even 

lower than those reported for the animals. 

Other adverse health effects on the eye, heart rate, and the central nervous system 

have been observed in laboratory animals exposed to electromagnetic energy at 

higher frequencies in the microwave region of the electromagnetic spectrum (see 

Section IV.A of the attached Appendix). The extent to which these latter effects 

may also be caused by absorption of energy at the lower frequencies employed by 

RF sealers is not known. 

There is no convincing evidence to indicate that RF energy can cause cancer in 

humans. 4 Reports have described chromosomal abnormalities in animal and human . 11 12 cells cultured m the laboratory after exposure to RF energy. ' However, the 

relevance of such studies to humans is not known and must be determined through 

additional research. 

There have been reports which suggest an association between RF exposure and 

reproductive damage in animals and humans. These reports, primarily from 

3 
Eastern Europe and the Soviet Union, list a variety of reproductive and 

developmental effects resulting from occupational exposures of workers and 

experimental exposures of laboratory animals to electromagnetic energy at 

frequencies in the RF and microwave :ttanges. Reported effects from exposure of 

women to fields of relatively high intensity RF and microwave energy have 

included changes in menstrual pattern, increased incidence of miscarriage, and 

decreased lactation in nursing mothers. 13 Retarded fetal development and 

increased congenital anomalies have been noted among exposed offspring. 1 3 

Laboratory studies have shown that exposure of pregnant rats to RF energy (at 

levels believed to have been relatively high) resulted in numerous fetal malformations including abnormalities of the central nervous system, eye deformities, cleft 

palate, and deformation of the tail. 14 

There is a report of changes in spermatogenesis (production of male germ cells in 

the testicles) among workmen exposed to nonionizing electromagnetic energy.

15 

Reproductive effects in male experimental animals, including testicular damage, 

debilitated or stillborn offspring and changes in spermatogenesis, have been 

reported to be related to exposure to electromagnetic energy at microwave 

frequencies. 16 '

17 Similar studies have not been reported for the lower frequencies 

of RF sealers and heaters. 

NIOSH surveys indicate that a large majority of the workers using RF sealing and 

heating equipment are women of child-bearing age. 18 NIOSH is beginning an 

epidemiologic study of potential reproductive effects among operators of RF 

sealers, and is conducting laboratory research to study the possibility that 

teratogenic effects (malformations) in animals may result from ex-posure to RF 

radiation. 

PRESENT OCCUPATIONAL EXPOSURE STANDARD 

The Occupational Safety and Health Administration radiation protection standard 

for occupational exposure to RF and microwave radiation (29 CFR 1910.97) applies 

to the frequencies 10 - 100,000 MHz. It establishes as a limit for occupational 

exposures a maximum power density of 10 mW/ cm 

2 , as averaged over any possible 

6-minute period. 19 In the far field, a power density of 10 mW/cm2 is equivalent to 

a mean squared electric field strength of 40,000 volts 2 /meter 2 or a mean squared 

magnetic field strength of 0.25 amperes

2 /meter 2 • OSHA is presently enforcing 

both of these mean squared field strengths averaged over any 0.1-hour period, as 

exposure limits for RF energy, under its occupational standard for nonionizing 

radiation (29 CFR 1910.97). 

Existing national health standards for RF energy have been based on evidence of 

the thermal effects which result from the body's absorption of RF energy and the 

subsequent heating of deep body tissue. However, in recent years since the 

development of existing national standards, concern has increased over reported 

"nonthermal" effects, which may occur at exposure levels lower than those causing 

measurable thermal effects. 

4 
NIOSH RECOMMENDATIONS 

NIOSH and OSHA are concerned about potential health hazards to workers exposed 

to RF energy emitted from RF sealers and heaters. The present Federal standard 

was derived using data principally from experiments with animals at microwave 

frequencies, not at the lower radiofrequencies. The standard was intended to 

prevent thermal effects. 

The extent to which biological effects attributed to the absorption of RF energy by 

animals reflect an occupational hazard to workers is not fully known. There are 

uncertainties in extrapolating experimental results from animals to humans and to 

frequencies other than those used in the experiments. These problems have been 

compounded by the difficulty in properly measuring near-field RF energy 

exposures, which has been only recently resolved. NIOSH recommends that future 

research projects dealing with · RF energy meet requirements for: 1) better 

exposure dosimetry and quantification of biological results, 2) use of adequate 

experimental controls, and 3) uniform reporting of experimental parameters and 

results. 

While scientists are not in complete agreement on the interpretation of available 

data on biological effects, NIOSH believes there is sufficient evidence of such 

effects to cause concern about human exposures. NIOSH and OSHA recommend 

that precautionary measures, as listed in Section V of the attached Appendix, be 

instituted to protect workers from unwarranted exposure to RF energy. 

Rn~~~ Anthony Robbins, M.D. 

Director 

National Institute for Occupational 

Safety and Health 

5 

8a Bingham; PL- . L,<-,m..-+-

Assistant Secret r of Labor 

Occupational Safety and Health 

Administration 
1. 

2. 

REFERENCES 

Conover, D.L., W.H. Parr, E.L. Sensintaffer, and W.E. Murray, Jr.: Measurement of Electric and Magnetic Field Strengths From Industrial 

Radiofrequency (15-40.68 MHz) Power Sources. In Biological Effects of 

Electromagnetic Waves: Selected Papers of the USNC/URSI Annua:1 Meeting 

(Boulder, Co., October 20-23, 1975). C.C. Johnson and M.L. Shore, eds., 

Department of Health, Education, and Welfare, Public Health Service, Food 

and Drug Administration, Bureau of Radiological Health, DHEW Publication 

(FDA) No. 77-8011, ~:356-362 (1976). 

Conover, D.L.: RF (10-40 MHz) Personnel Exposure. 

Problems, American Industrial Hygiene Association 

Orleans, La., May 22-27, 1977, 10 pp. (1977). 

Industrial Hygiene 

Conference, New 

3. Schwan, H.P.: Microwave Bioeffects Research: Historical Perspectives on 

Productive Approaches. {· Microwave Power 14(1):1-5 (1979), 

4. National Institute for Occupational Safety and Health (NIOSH): NIOSH 

Technical Report, Carcinogenic Properties of Ionizing and Non-ionizing 

Radiation, Volume II Microwave and Radiofrequency Radiation. 

Department of Health, Education, and Welfare, Public Health Service, Center 

for Disease Control, National Institute for Occupational Safety and Health, 

DHEW (NIOSH) Publication No. 78-134 (March 1978). 

5. Dodge, C.H. and Z.R. Glaser: Trends in Nonionizing Electromagnetic 

Radiation Bioeffects Research and Related Occupational Health Aspects. J. 

Microwave Power 12(4):319-334 (1977). 

6. Serdiuk, A.M.: Biological Effect of Low-intensity Ultrahigh Frequency 

Fields. Vrach. Delo !!_:108-111 (1969), 

7. Lobanova, E.A., and A.V. Goncharova: Investigation of Conditioned-reflex 

Activity in Animals (Albino Rats) Subjected to the Effect of Ultrashort and 

Short Radio-waves. Gig. Tr. Prof. Zabol. _!i(l):29-33 (1971). 

8. Demokidova, N.K.: The Effects of Radiowaves on the Growth of Animals. In 

Biological Effects of Radiofrequency Electromagnetic Fields, Z.V. Gordon, 

ed., Arlington, Va., U.S. Joint Publications Research Service No. 63321, pp, 

237-242 (1974). 

9. Volk9va, A.P., and P.O. Fukalova: Changes in Certain Protective Reactions 

of an Organism Under the Influence of SW in Experimental and Industrial 

Conditions. In Biological Effects of Radiofrequency Electromagnetic Fields, 

Z.V. Gordon, ed., Arlington, Va., U.S. Joint Publications Research Service No. 

63321, pp. 168-174 (1974). 

6 
10. Durney, C.H., C.C. Johnson, P.W. Barber, H. Massoudi, M.F. Iskarder, and 

J.C. Mitchell: Radio frequency Radiation Dosimetry Handbook, 2nd ed., SAMTR-78-22. Brooks Air Force Base, Tx., Department of the Air Force, Air 

Force Systems Command, Aerospace Medical Division, School of Aerospace 

Medicine, 141 pp. (1978). 

11. Heller, J .H.: Cellular Effects of Microwave Radiation. In Biological Effects 

and Health Implications of Microwave Radiation: Symposium Proceedings 

(Richmond, Va., September 17-19, 1969). S.F. Cleary, ed., Department of 

Health, Education, and Welfare, Public Health Service, Food and Drug 

Administration, Bureau of Radiological Health, Division of Biological Effects 

(BRH/DBE 70-2),pp. 116-121 (1970). 

12. Mickey, G.H., J.H. Heller, and E. Snyder: Non-Thermal Hazards of Exposure 

to Radio Frequency Fields - Final Report. New England Institute, 

Ridgefield, Ct., 46 pp. (1975). Submitted to Department of the Navy, Office 

of Naval Research Under Contract No. N00014-69-C-0175. 

13. Marha, K., J. Musil, and H. Tuha: Electromagnetic Fields and the Life 

Environment. State Health Publishing House, Prague, Czechoslovakia, 1968. 

Translation SBN 911302-13-7, San Francisco Press, Inc., San Francisco, Ca., 

(1971). 

14. Dietzel, F ., W. Kern, and . R. Steckenmesser: Deformity and Intrauterine 

Death Following Short-wave Therapy in Early Pregnancy in Experimental 

Animals. Muench. Med. Wochenschr, 114:228-230 (1972). 

15. Lancranjan, I., M. Maicanescu, E. Rafaila, I. Klepsch, and H. Popescu: 

Gonadic Function in Workmen With Long-term Exposure to Microwaves. 

Health Physics 29:381-383 (197 5). 

16. Bereznitskaya, A.N. and I.M. Ka zbekov: Studies on the Reproduction and 

Testicular Microstructure of Mice Exposed to Microwaves. In Biological 

Effects of Radiofrequency Electromagnetic Fields, Z.V. Gordon, ed., 

Arlington, Va., U.S. Joint Publica tions Research Service No. 63321, pp. 221-

229 (1974). 

17. Varma, M.M. and E.A. Traboulay, Jr.: Biological Effects of Microwave 

Radiation on the Testes of Swiss Mic e. Experientia l!:301-302 (1975). 

18. Division of Biomedical and Behavioral Science, National Institute for 

Occupational Safety and Health: Testimony at Hearings Before the 

Committee on Commerce, Science, and Transportation, United States Senate; 

First Session on Oversight of Radiation Health and Safety, June 16, 17, 2 7, 

28, and 29, 1977. Government Printing Office, Serial No. 95-49, pp. 582-587 

(1977). 

19, U.S. Department of Labor, Occupational Safety and Health Administration: 

OSHA Safety and Health Standards, 29 CFR 1910,97, OSHA 2206, Revised, 

November 7, 1978, Washington, D.C. 

7 
APPENDIX 

JOINT NIOSH/OSHA CURRENT INTELLIGENCE BULLETIN =lf:33 

Radiofrequency (RF) Sealers and Heaters: 

Potential Health Hazards and Control 

I. Manufacturers of Radiofrequency Sealing and/or Heating Equipment 

Il. Occupations Which May mvolve Use of Radiofrequency Sealing and Heating 

Equipment 

m. Manufacturers of mstruments for Measurement of Radiofrequency Energy in 

the Near Field 

IV. Supporting Technical mformation 

A. Electromagnetic Radiation 

B. RF Sealers and Heaters 

C. Measurements of RF Energy Fields 

D. · Absorption of RF Energy 

E. Biological Effects of Absorbed RF Energy 

V. Recommendations for Hazard Control 

References 

8 
I. Manufacturers of Radiofrequency 

Sealing and/or Heating Equipment 

Mention of company name or product does not constitute endorsement by the 

National Institute for Occupational Safety and Health or the Occupational Safety 

and Health Administration. 

Chemetron Corp. (Voltator), 

Compo Industries, Inc. 

Cosmos Electronic Machine Corporation 

Duomatic Electronics Corporation 

Gallery Services Fara-Dine 

Gerling Moore, Inc. 

Guild Electronics, Inc. 

Hall Dielectric Machine Company 

J .A. Callanan Company 

Kabar Manufacturing Corporation 

Lepel High Frequency Laboratories, Inc. 

Mann-Russell Electronic Devices, Inc. 

Pillar Corporation 

P.S.C. Inc. 

Radio Frequency Company, Inc. 

Seal-Pac Services and Machine, Inc. 

Solidyne, Inc. 

Divisions: Thermatron 

Sealomatic 

Faratron 

Stanelco, Ltd 

Colpitt, B.V. 

Thermo Dielectric Machine Company, Inc. 

Welduction, Inc. 

W.T. LaRosa and Associates, Inc. 

Louisville, Kentucky 

Waltham, Massachusetts 

Farmingdale, New York 

Brooklyn, New York 

So. El Monte, California 

Santa Clara, California 

Brooklyn, New York 

Deer Park, New York 

Chicago, Illinois 

Farmingdale, New York 

Maspeth, New York 

Tacoma, Washington 

Milwaukee, Wisconsin 

Cleveland, Ohio 

Medfield, Massachusetts 

Brooklyn, New York 

Bay Shore, New York 

Brooklyn, New York 

Plymouth, Michigan 

Troy, New York 

*This list is complete and accurate to the best knowledge of NIOSH; however, 

there may be other manufacturers of this equipment of which the Institute is not 

aware. 

9 
II. Occupations Which May Involve Use of 

Radiofrequency Sealing and Heating Equipment 

Automotive workers 

Drying of trim base panels Embossing of heel pads to carpets 

Heat sealing body interior trim panels Heat sealing convertible tops and vinyl 

roofs 

Heat ~ealing upholstery covers for seats 

and backs 

Furnitu~e and wood workers 

Decking assembly 

Door lamination 

Fabrication of posts and rafters 

Fiberboard fabrication 

Laminated beams 

Lumber edge glueing Plywood panel patching Plywood or particleboard scarf glueing Ski lamination 

Veneer panel glueing 

Glass fiber workers 

Drying and curing sizing on machine 

packages Drying coatings on continuous moving 

strands 

Drying glass fibers on forming tubes 

Drying roving packages 

Paper product workers 

Correcting moisture profile on 

continuously moving webs 

Drying resin coatings Drying twisted twine packages Gluing paper Heating coating on continuous webs 

Plastic heat-sealing workers involved in the 

manufacture/fabrication of: 

Acetate box covers 

Advertising novelties 

Appliance covers 

Aprons 

Baby pants Beach balls 

Belts and suspenders Blister packages 

Book covers 

Capes 

Charge cards 

Checkbook covers 

Convertible tops 

Cushions 

Diaper bags Display boxes 

Electric blankets 

Food packages 

Fountain pens Garment bags 

Gas masks 

Goggles (industrial) 

10 

Plastic heat-sealing workers (continued) 

Handbags 

Hat covers 

Index cards 

Lampshades 

Liquid containers 

Luggage 

Machine covers 

Mattress covers 

Mild cartons 

Oxygen tents 

Packages 

Pharmaceuticals 

Pillowcases 

Pillow packages Pl as tic gloves Pool liners 

Protective clothing Racket bags Rain apparel Refrigerator bags Shoe bags 

Shoes 

Shower curtains 

Sliocovers 

Splatter mats 

Sponge backings Sport equipment Tobacco pouches 

Toys 

Travel cases 

Umbrellas 

Wallets 

Waterproof containers 

Wire terminal covers 

RF/microwave application workers 

Advertising . RF-excited gas display signs Ceramics. Drying of ceramic objects Chemical. Activation of chemical 

reactions 

Electronics. Tube ~ging and testing 

Laser. RF-excited gas lasers 

Medical . Diathermy and (experimental) 

cancer therapy Scientific equipment. Low temperature ashing of samples 

Welding. RF-stabilized welding 

Rubber products workers 

Drying latex foams 

Gelling latex foams 

Preheating prior to curing latex foams 

Preheating prior to molding 

Textile workers 

Drying continuous webs 

Drying impregnated or coated yarns 

Drying rayon cake packages Drying slasher coatings Drying wound packages 
m. Manufacturers of Instruments for 

Measurement of Radiofrequency Energy in 

the Near Field* 

Mention of company name or product does not constitute endorsement by the 

National Institute for Occupational Safety and Health or the Occupational Safety 

and Health Administration. 

General Microwave Corp. 

Farmingdale, Long Island, New York 

For electric field only: 

High sensitivity isotropic radiation hazard meter, Model 4 

Instruments for Industry, Inc. 

Farmingdale, Long Island, New York 

For electric field only: 

Electric field radiation hazard monitor, Model RHM-2 

Narda Corporation 

Plainview, Long Island, New York 

For electric and magnetic fields: 

Electric field strength probe, Model 8644 

Magnetic field strength probes, Model 8635 or 8633 

Readout meters, Model 8619 or Model 1816 

*This list is complete and accurate to the best knowledge of NIOSH: however, 

there may be other manufacturers of comparable equipment of which the Institute 

is not aware. 

11 
IV. Supporting Technical Information 

A. ELECTROMAGNETIC RADIATION 

Radiofrequency energy (or RF radiation) is part of the electromagnetic energy 

spectrum. With regard to the energy emitted from a RF sealer or heater, 

electromagnetic radiation may be considered as a series of waves of energy 

propagated through space and composed of oscillating electric and magnetic fields. 

These waves are produced by moving electric charges, and may be of natural origin 

(e.g. the sun), or may be of human origin (e.g. produced by electronic devices such 

as diathermy machines, microwave ovens, and television and radio transmitters). 

The wave of electromagnetic energy is characterized, in part, by: 

1) the strengths of the electric and magnetic fields -- the 

intensity of electromagnetic forces 

2) the frequency of oscillation - the number of complete oscillations per 

second of the wave 

3) the wavelength - the distance between two consecutive 

peaks of the wave 

Wavelength and frequency are inversely related; as the wavelength increases, the 

frequency decreases. The energy content of electromagnetic radiation is related 

to wavelength; waves of longer wavelength (lower frequency) contain less energy 

per quantum* unit. A graphic representation of the electromagnetic radiation 

spectrum is presented in Figure 1. 

FREQUENCY (Hertz, cycle per second) 

(!MIiz)* ( 1000 MHz) 

103 106 1012 1015 1018 

.----,--rr-.C.,---.--~~.---,TT"r-r-TT""...---.---.----'~-.--,-,"",----.----.---, I ltra I I I I 

AC Power 

I Infra 

red 

I ~iolet1 1 Vfsfbl e I X-Rays : I I I I I I I t 

3xto8 3x 105 3r. 102 I I 3x10-l 

Most RF Sealers _..,.~ 

3xto-4 3xto-7 3xIO-I0 

and Heaters __,,...,. 

WAVELENGTH (meters) onionfzfng I Ionfzfng ' 

Radfatfon Radfatfon 

*!MHz = 1,000,000 Hz = 106 llz 

Figure I The Electromagnetic Spectrum 

Electromagnetic energy emitted from a source propagates through space until it is 

absorbed, reflected, transmitted and/or diffracted by objects in its path. When 

*Electromagnetic energy can also be described as discrete particles (or quanta) of 

energy. 

12 
electromagnetic radiation contains sufficient energy (at frequencies much higher 

than radiofrequencies), it can ionize atoms of the material absorbing the energy 

(i.e. dislodge electrons from the atoms of the absorbing material). Radiation of 

sufficient energy to cause ionization of molecules in biological tissue is often 

referred to as ionizing radiation, whereas radiation of insufficient energy to cause 

this effect is referred to as nonionizing radiation. The ionizing and nonionizing 

regions of the electromagnetic spectrum are shown in Figure 1. While noni0!lizing 

radiation absorbed by biological tissue is not capable of ionizing atoms or 

molecules, it nevertheless may produce changes in the vibrational and rotational 

energies of the biological molecules, leading to changes in the molecules or 

dissipation of the energy in the form of heat. 

B. RF SEALERS AND HEATERS 

RF sealers and heaters generate, by means of electronic circuitry, oscillating fields 

of electric and magnetic energy. RF sealers generally operate within the band of 

frequencies from 10 to 70 MHz (a megahertz (MHz) is one million cycles per 

second), although most of the sealers operate at nominal frequencies from 13 to 40 

MHz. A few wood glueing machines operate at frequencies as low as 3 - 6 MHz, 

and a few RF heaters used for plastics operate at frequencies as high as 300 - 400 

MHz. RF electromagnetic energy emitted from an RF sealer or heater is 

considered nonionizing radiation by virtue of its frequency and quantum energy. 

Unshielded or improperly shielded RF sealers or heaters can leak stray RF energy. 

Measurements have been made of electric and magnetic field strengths, in the 

immediate area of an operator, as great as 2000 volts/meter and 10 

amperes/meter, respectively. 1 '

2 The majority of surveyed RF machines leaked 

stray energy in excess of 200 volts/meter or 0.5 amperes/meter. 2 Measurements 

of electric and magnetic field strengths will be discussed below. 

C. MEASUREMENTS OF RF ENERGY FIELDS 

hl the measurement of RF energies, the distances from the RF source at which the 

measurements are being made must be considered. For purposes of this Bulletin, 

distances from the RF source can be categorized as being either far field or near 

field. The far field includes all distances from the RF source greater than 

approximately ten times the wavelength. Wavelengths corresponding to frequencies 

used by RF sealers and heaters may range from about one meter to a few hundred 

meters. The frequency of 27 MHz, which is typical for many RF heaters, is 

associated with a nominal wavelength of about 11 meters. hl the far field, the 

amount of energy associated with the typical wave can be expressed as a power 

density (with the units of milliwatts per square centimeter, mW /cm2). The value 

of the power density in the far field can be measured with a power density monitor, 

or can be calculated from measurement of the intensity of either the electric field 

or the magnetic field alone. The strength of the average electric field is expressed 

in units of volts/meter with the mean squared value expressed in volts 2 /meter 2

; 

the strength of the average magnetic field is expressed in units of amperes/meter 

with the mean squared value expressed in amperes

2 /meter 2 • 

13 
The near field comprises distances from the RF source less than about five 

wavelengths, which includes the immediate vicinity of the RF .device where most 

worker exposures to RF energy occur. In the near field, electromagnetic waves 

have different characteristics than in the far field. Furthermore, in the occupational setting near a RF sealer or heater, the electromagnetic field generally is not 

uniform, and the energy field incident upon a worker is complex and depends on 

many factors. A power density monitor, designed for use in the far field, is likely 

to give exceedingly inaccurate measurements in the near field. Further, in the 

near field, as opposed to the far field, there is no simple mathematic equivalency 

between values of power density and measurements of either electric or magnetic 

field strength. 

In the past, values of far-field power density have been used in various public 

health guides and recommendations for exposure limits, including those intended 

for occupational settings. However, a power density value, which can be measured 

or calculated for far-field conditions, is not appropriate for quantifying near-field 

exposure of a worker operating an RF sealer or similar device. In the near field, 

measurements of both the electric and the magnetic fields are necessary to 

properly characterize worker exposure conditions. Instruments are now 

commercially available to make near-field measurements of the electric and 

magnetic fields. Users should follow instrument manufacturers' use instructions 

carefully to avoid damage of sensitive instrument probes. A list of manufacturers 

of these instruments is presented in Section ill of the Appendix. 

D. ABSORPTION OF RF ENERGY 

When RF energy propagating through space encounters an object, it may be 

reflected by the object (forced to change direction of travel), transmitted through 

the object, or absorbed by the' object. The extent to which RF energy is reflected, 

transmitted, and/or absorbed depends on the frequency of the RF energy, and on 

the shape, size, and dielectric properties of the object as well as its orientation 

relative to the incident RF energy. 

Humans can absorb RF energy at the frequencies used by most RF sealers and 

heaters. In workers who are not in contact with an electrical ground, the highest 

absorption rates for whole-body irradiation can occur at frequencies between 60 

and 100 MHz with a peak at approximately 80 MHz. 3 ,1+ These frequencies of high 

absorption rates are very close to the frequencies used by most sealers and heaters. 

Hence, workers near RF sealers and heaters can absorb considerable amounts of 

the stray energy emitted from the RF machines. Effects of directly touching an 

electrical ground plane can lower, by as much as one half, the frequency at which 

an irradiated body will maximally absorb energy. 

3 Contact of the worker with an 

electrical ground plane can shift the frequency of maximum absorption rate to well 

within the frequency band of most RF sealers and heaters; this could increase the 

amount of energy absorbed by the worker and worsen the exposure condition. RF 

shielding material incorporated into the floor, walls, and ceiling of some RF 

workrooms could constitute such a ground plane. 

14 
E. BIOLOGICAL EFFECTS OF ABSORBED RF ENERGY 

Details of some experiments performed in laboratory animals with low intensity RF 

energy at frequencies commonly used with sealers and heaters are summarized in 

the following table. 

Table 1. Some Reported Biologic Effects in Animals Exposed to RF Energy at Frequencies in the Range of IO to 70 MHz 

Frequency 

(Wavelength) 

50 MHz 

( 4 . 3 meters) 

69.7 MHz 

69 .7 MHz 

14.88 MHz 

14 .88 MHz 

Exposure Conditions 

0.5-6 volts/meter 

for 10-12 hrs/day; 180 days 

150 volts/meter 

for 60 min/ day; 4 months 

12 volts/meter 

for 1 hr/day; 1.5 months 

48 vo 1 ts/meter 

for 4 hrs/day; 1. 5 months 

70 volts/meter 

100 volts/meter 

for 4 hrs/day; 10 months 

llnimal 

rats and/or 

rabbits 

rats 

rats 

infant 

rats 

infant 

rats 

rats 

15 

Reported Effects 

changes in conditioned reflexes 

changes in encephalograms 

decreased blood cholinesterase 

activity 

increased urine 17-ketosteroids 

decreased leukocyte count 

decreased phagocytic activity 

changes in conditioned reflexes 

increases weights of adrenal 

and pituitary glonds 

dec reased weight of thyroid gland 

increased weight of adrenal gland 

decreased weights of thyroid and 

ad renal glands 

changes in phagocytic activity 

Reference 

5 

6 

7 

7 

8 
V. Recommendations for Hazard Control 

Immediate Actions 

Control of the emission of RF energy from RF sealers and heaters should rely on 

the application of properly designed and installed shielding material. The shielding 

should be placed on or around the equipment so as to minimize occupational 

exposure due to emissions of stray RF energy. All shielding material should be 

properly grounded. Shielded conductors should be used for conveying RF current, 

and path impedance should be minimized by using good conductor materials. Many 

of these control features are available on RF sealers and heaters being marketed 

new, and some machines already in use can be retrofitted with some of these 

features. Older machines may require custom modification to control stray 

emissions. 

The distance between the worker and the source of RF energy emission should be 

maximized. Examples of means to accomplish this include the use of automatic 

feeding devices, rotating tables, and remote materials handling. 

The RF sealing and heating equipment should be electronically tuned to minimize 

the stray power emitted. 

Whenever possible, equipment should be switched off when not being used. 

Maintenance and adjustment of the equipment should be performed. only while the 

equipment is not in operation. 

After the performance of maintenance or repair, all machine parts, including 

cabinetry, should be reinstalled so that the equipment is intact and its 

configuration is unchanged. 

Warnings and Information 

Access to the vicinity of RF sealers and heaters where there may be stray RF 

energy should be limited as much as possible to the operator and necessary 

assistants, maintenance personnel, and industrial hygiene or safety personnel. Use 

of the RF equipment should be restricted to properly trained personnel. 

Areas in which exposures to RF energy have been determined to be appreciable 

should be posted. Any signs should be of such size as to be recognizable and 

readable from a distance of three meters. All warning signs must be printed in 

English and in the predominant languages of non-English-reading workers, and 

should conform to the design recommended by OSHA. 9 

Areas in which the RF energy is present at levels higher than the permissible 

exposure limit also should be posted. The warning signs should contain the 

following additional jnformation: HAZARD--DO NOT ENTER. The sign must be 

16 
readable from a distance of three meters. The perimeter of the restricted area 

should be clearly demarcated with signs visible to all personnel approaching the 

area. 

Medical Monitoring 

A medical surveillance program, tailored to the expected degree of employee use 

of RF equipment and potential for exposure to RF energy, should be developed. 

The program should include preplacement examination of all new employees and an 

initital examination of all present employees subject to occupational exposure to 

RF energy. In an effort to identify possible adverse effects associated with 

exposure to RF energy, annual examinations should be considered for workers who 

may be exposed to RF energy on a regular, long-term basis. Work histories should 

be included in all examinations. 

Medical histories and physical examinations should give particular emphasis upon 

target organs potentially affected by RF energy including the eye (cataracts), the 

central nervous system, the blood (decreased leukocyte count), the immune defense 

system, and the reproductive system. Adverse reproductive effects may involve 

both maternal and paternal exposure. For persons occupationally exposed to RF 

energy, medical records including health and work histories should be maintained 

throughout the period of employment and for an extended period after termination 

of employment, 

Exposure Measurements 

Areas in the occupational environment where levels of RF energy have been 

determined to be appreciable should be surveyed at regular intervals. Immediately 

following a physical or electronic alteration of the equipment or an alteration in 

the process, a complete survey should also be performed. If measurements taken 

during a survey indicate that occupational exposure exceeds the permissible 

exposure limit, a second survey should be made on the next workday. If the limit is 

still exceeded, the use of RF equipment producing excessive values should be 

prohibited until appropriate controls have been instituted. The survey data sheets 

should contain all information pertaining to the survey, and should include the date 

and time of measurement, the type of monitoring equipment used, the employees' 

names, and the remedial actions taken, if any. These records should be maintained 

for an extended period of time. 

17 
REFERENCES 

1. Conover, D.L., W.H. Parr, E.L. Sensintaffer, and W.E. . Murray, Jr.: 

2. 

Measurement of Electric and Magnetic Field Strengths From Industrial 

Radiofrequency (15-40.68 MHz) Power Sources. In Biological Effects of 

Electromagnetic Waves: Selected Papers of the USNC/URSI Annual Meeting 

(Boulder, Co., October 20-23, 1975). C.C. Johnson and M.L. Shore, eds., 

Department of Health, Education, and Welfare, Public Health Service, Food 

and Drug Administration, Bureau of Radiological Health, DHEW Publication 

(FDA) No. 77-8011, ~:356-362 (1976). 

Conover, D.L.: RF (10-40 MHz) Personnel Exposure. 

Problems, American Industrial Hygiene Association 

Orleans, La., May 22-27, 1977, 10 pp. (1977). 

Industrial Hygiene 

Conference, New 

3. Gandhi, O.P.: Conditions of Strongest Electromagnetic Power Deposition in 

Man and Animals. IEEE Trans. Microwave Theory Tech. 23:1021=1029 (1975). 

4. Durney, C.H., C.C. Johnson, P.W. Barber, H. Massoudi, M.F. Iskarder, and 

J.C. Mitchell: Radiofrequency Radiation Dosimetry Handbook, 2nd ed., SAMTR-78-22. Brooks Air Force Base, Tx., Department of the Air Force, Air 

Force Systems Command, Aerospace Medical Division, School of Aerospace 

Medicine, 141 pp. (1978). 

5. Serdiuk, A.M.: Biological Effect of Low-intensity Ultrahigh Frequency 

Fields. Vrach. Delo .!.!_:108-111 (1969), 

6. Lobanova, E.A., and A.V. Goncharova: Investigation of Conditioned-reflex 

Activity in Animals (Albino Rats) Subjected to the Effect of Ultrashort and 

Short Radio-waves. Gig. Tr. Prof. Zabol, li(l):29-33 (1971). 

7. Demokidova, N.K.: The Effects of Radiowaves on the Growth of Animals. In 

Biological Effects of Radiofrequency Electromagnetic Fields, z:v. Gordon, 

ed., Arlington, Va., U.S. Joint Publications Research Service No. 63321, pp. 

237-242 (1974). 

8. Volkova, A.P., and P.O. Fukalova: Changes in Certain Protective Reactions 

of an Organism Under the Influence of SW in Experimental and Industrial 

Conditions. In Biological Effects of Radiofreguency Electromagnetic Fields, 

Z.V. Gordon, ed., Arlington, Va., U.S. Joint Publications Research Service No. 

63321, pp. 168-174 (1974). 

9, U.S. Department of Labor, Occupational Safety and Health Administration: 

OSHA Safety and Health Standards, 29 CFR 1910.97. OSHA 2206, Revised, 

November 7, 1978, Washington, D.C. 

18 
CUMULATIVE LIST OF NIOSH CURRENT INTELLIGENCE BULLETINS 

1 . Chloroprene 

2. Trichloroethylene (TCE) 

3. Ethylene Dibromide (EDB) 

4. Chrome Pigment 

5. Asbestos - Asbestos Exposure during Servicing 

of Motor Vehicle Brake and Clutch Assemblies 

6. Hexamethylphosphoric Triamide (HMPA) 

7. Polychlorinated Biphenyls (PCBs) 

8. 4,4'-Diaminodiphenylmethane (DOM) 

9. Chloroform 

10. Radon Daughters 

11. Dimethylcarbamoyl Chloride (DMCC) 

Revised 

12. Diethylcarbamoyl Chloride (DECC) 

13. Explosive Azide Hazard 

14. Inorganic Arsenic - Respiratory 

Protection 

15. Nitrosamines in Cutting Fluids 

16. Metabolic Precursors of a Known Human 

Carcinogen, Beta-Naphthy la mine 

17. 2-Nitropropane 

18. Acrylonitrile 

19. 2,4-Diaminoanisole in Hair and Fur Dyes 

20. T etrachloroethy lene (Perchloroethy lene) 

21. Trimellitic Anhydride (TMA) 

22. Ethylene Thiourea (ETU) 

23. Ethylene Dibromide and Disulfiram 

Toxic Interaction 

24. Direct Black 38, Direct Blue 6, and 

Direct Brown 95 Benzidine Derived Dyes 

25. Ethylene Dichloride (1,2-Dichloroethane) 

26. NIAX ® Catalyst ESN 

27. Chloroethanes - Review of Toxicity 

28. Vinyl Halides - Carcinogenicity 

29. Glycidyl Ethers 

30. Epichlorohydrin 

31. Adverse Health Effects of Smoking and 

the Occupational Environment 

32. Arsine (Arsenic Hydride) Poisoning in the 

Workplace 

33. Radiofrequency (RF) Sealers and Heaters: 

Potential Health Hazards and Their Prevention 

- January 20, 197 5 

- June6,1975 

- July 7, 197 5 

- June 24, 1975 

- October 7, 1975 

- October 8, 1976 

- August 8, 197 5 

- October 24, 197 5 

- November 3, 197 5 

- August 20, 1976 

- January 30, 197 6 

- March 15, 1976 

- May 11, 1976 

- July7,1976 

- July7,1976 

- August 16, 1976 

- September 27,197 6 

- October 6, 1976 

- December 17,1976 

- April 25, 1977 

- July 1, 1977 

- January 13, 1978 

- January 20, 1978 

- February 3, 1978 

- Aprilll,1978 

- April 11, 1978 

- April 17, 1978 

- April 19, 1978 

- May 22, 1978 

- August 21, 1978 

- September 21,1978 

- October 12, 1978 

- October 12, 1978 

- February 5, 1979 

- August 3, 1979 

- December 4, 1979 

NOTE: Bulletins II l through 1118 have been reprinted as a NIOSH publication, 1178-

127, for the convenience of those that desire a complete series of Current 

Intelligence Bulletins. Distribution of this publication and single copies of 

Bulletins 1119 and later are available from NIOSH Publications 

Dissemination, Division of Technical Services, 4676 Columbia Parkway, 

Cincinnati, Ohio 45226. 
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