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Home My WebLink AboutCUP 02-06; CALLAWAY VERIZON WIRELESS; ANALYSIS OF RADIOFREQUENCY ENVIRONMENT; 2002-06-17. eApert VA km Sohfflsis Inc A Tetra Tech Company 2030 cr Ava**e, Polygon Plaza suite 120 Fan Lac, New Jaey () (201)944.1750 (F)(201)944-6619 An Analysis of Radiofrequency Environment in the Vicinity of a Proposed Cellular Radio Base Station Site Name : Callaway Carrier: Verizon Wireless 2180 Ruifleifonl Road, Catisbad, CA 92008 0 Presented to: Tetra Tech Wireless 0 TABLE OF CONTENTS Introduction: .....................................................................................3 Technical / Site Data: ........... ............ ................................................... 4 Analysis and Computation ................................................................... 4 FCC Policy on Human Exposure to Radio Frequency EMF ............................ 8 Discussion of Safety Criteria ............................................................. 9 Remarks and Conclusions: ............................................................... 10 Glossary of Terms ................................................................. 10 Certification: ............. ................... ...... .... --- ............. ............... 12 References............................................................. 13 Attachments ..... ....... ...................................... ............... 14 . 2 10 Introduction: This report is an analysis of the radiofrequency (RF) environment surrounding the proposed installation of Verizon Wireless cellular radio facility (Callaway) at 2180 Rutherford Road, Carlsbad, CA 92008. Verizon Wireless is licensed by the Federal Communication Commission (FCC) to provide a wireless communications known as Cellular and Personal Communication Services (PCS). This report was generated in response to the request of Tetra Tech Wireless to provide an objective evaluation on Health and Safety for this particular site. As required by the FCC, all wireless system operators are required to perform an assessment on the potential human exposure to radiofrequency fields emanating from all transmitting antennas at the site. In addition, our task is to determine if the cell site proposed by Verizon Wireless complies to Federal Laws by applying the Maximum Permissible Exposure (MPE ) limits specified in the FCC's regulation. Verizon Wireless will be co-located with Verizon Microwave facility operating at this location. In the United States local and state jurisdictions have also enacted rules and regulations pertaining to human exposure to RF energy. However, the Telecommunications Act of 1996 contained provisions outlining the federal jurisdiction to regulate human exposure to RF emissions from certain transmitting devices.. In particular, Section 704 of the Act states that, "No State or local government or instrumentality thereof may regulate the placement, construction, and modification of personal wireless service facilities on the basis of the environmental effects of radio frequency emissions to the extent that such facilities comply with the Commission's regulations concerning such emissions." Moreover, the purpose of this report is to ensure that the RF environment associated with this facility complies with the Federal Communications Commission (FCC) guidelines as required by the Telecommunication Act of 1996, which is the same safety criteria used by the State of California Department of Health. . n • Site Data: The data below enumerates the specifications of the Proposed Verizon Wireless facilities at 2180 Rutherford Road, Carlsbad, CA 92008. Verizon Wireless antennas will be mounted at the height of 39 ft. while Verizon Microwave antenna will be at 45 ft, above ground level. iTechniea1 Snecifications: Verizon Wireless (Callaway) Description Maximum ERP per channel 209 Watts Actual radiated power per channel 18.7 watts Actual total radiated power per sector 112 watts Number of Tx/Rx antennas (duplexed) I per sector Number of transmitters 6 per sector Number of sectors configured 3 Antenna centerline height above grade 39 (All sectors same height in ft) Antenna Manufacturer EMS Model Number MTFR90-1 1-USDA Gain 10.5 dBd I 1165 dBi Type H90, V15 DualPol Downtilt 0 degrees h.. Technical Specifications : Verizon Microwave Facility Scil Maximum ERP 43 watts Actual radiated power 0.05 watts Antenna centerline height above grade 45 ft. above ground level Antenna Manufacturer Andrew Model Number HP2 - 102 Gain 33.3 dBi Type Single Polarized Downtilt 0 degrees Analysis and Computation: Based on the emissions pattern of the antenna supplied, the majority of the energy dispersed is propagated towards the horizon. This statement assumes zero mechanical downtilt is applied to the specified sector. If mechanical downtilt is applied, the maximum directivity of the energy will be normal to the plane of the antenna and is accounted for in the computation. Electrical downtilt will be accounted for within the antenna pattern specifications. Below is the formula used for the calculation of power density and the chart for the parameters used in the computation: . Power density is a measure of power divided by the surface area of the sphere or the unit area normal to the direction of propagation, usually expressed in units of milliwatts per square . ru centimeter ( mW/cm), watts per square meter (W/m 2) or microwatts per square centimeter (pW/cm2). I. Far-field (Ground Level) S = (GR *EIRp * AngRadFact) / (4 ltR2 ) where: S = power density ( mW/cm) EIRP (max) = maximum power coming out of the antenna (mW), maximum effective isotropic radiated power (Note: EIRP is 64% higher than ERP, which is reference to a half-wave dipole) Angular Radiation Factor = Numeric factor for antenna discrimination (EIRP reduction) in the vertical plane, applicable at downward angle to a 6' human standing on ground, calculated at distances from 0' to 500' away from the antenna R = straight line distance of the antenna from a 6 ft. human GR = Ground reflection = The ground reflection coefficient used in this study was four (4) vs the recommended 256, meaning we assumed a 100% reflection on the ground as opposed to 60%, recommended by the US Environmental Protection Agency. AVE % = Calculated exposure level, as a percentage of the FCC MPE limit for continuous exposure of the general population Li Ground level RF Power Density and percent-of-MPE calculations Antenna Array - Verizon Wireless G dist (ft.) R dist (ft.) I V angle AngRadFact S (mW/cm 2) MIPE % 0 33 90.0 0.00098 0.00064 0.03735 20 38.59 58.8 0.00200 0.00095 0.05578 40 51.86 39.5 0.02630 0.00692 0.40717 60 68.48 28.8 0.01349 0.00204 0.11975 80 86.54 22.4 0.04266 0.00403 0.23710 100 105.30 18.3 0.01202 0.00077 0.04513 120 124.45 15.4 0.00955 0.00044 0.02566 140 143.84 13.3 0.05248 0.00180 0.10559 160 163.37 11.7 0.09333 0.00247 0.14556 180 183.00 10.4 0.21878 0.00462 0.27193 200 202.70 9.4 0.29512 0.00508 0.29898 220 222.46 8.5 0.29512 0.00422 0.24823 240 242.26 7.8 0.38905 0.00469 1 0.27593 _ 260 262.09 7.2 0.48978 0.00505 I 0.29681 280 281.94 6.7 0.48978 0.00436 025648 300 301.81 6.3 0.58884 0.00457 0.26909 320 321.70 5.9 0.58884 0.00403 0.23685 340 341.60 5.5 0.58884 000357 0.21006 360 361.51 5.2 0.69183 0.00375 0.22036 380 381.43 5.0 0.69183 0.00336 0.19794 400 401.36 4.7 0.69183 0.00304 0.17877 420 421.29 4.5 0.77625 0.00309 0.18205 440 441.24 4.3 0.77625 0.00282 0.16597 460 461.18 4.1 ] 0.77625 0.00258 0.15192 480 481.13 3.9 0.77625 0.00237 0.13958 500 501.09) 3.8 0.77625 0.00219 0.12869 . . C 1.2 Ground level RF Power Density and percent-of-MPE calculations Antenna Array - Verizon Microwave Facility G dist (ft.) R dist (ft.) V angle AngRadFact S (mW/cm2) MPE % 0 39 90.0 0.00003 0.0000005 0.00005 20 20.00 62.9 0.00016 0.0000096 0.00096 40 40.00 44.3 0.00063 0.0000095 0.00095 60 60.00 33.0 0.00158 0.0000107 0.00107 80 80.00 26.0 0.00251 0.0000095 0.00095 100 100.00 21.3 0.00251 0.0000061 0.00061 120 120.00 18.0 0.00251 0.0000042 0.00042 140 140.00 15.6 0.00251 0.0000031 0.00031 160 160.00 13.7 0.00316 0.0000030 0.00030 180 180.00 12.2 0.00631 0.0000047 0.00047 200 200.00 11.0 0.00794 0.0000048 0.00048 220 220.00 10.1 0.01000 0.0000050 0.00050 240 240.00 92 0.01259 0.0000053 0.00053 260 260.00 8.5 0.01259 0.0000045 0.00045 280 280.00 7.9 0.01259 0.0000039 0.00039 300 300.00 7.4 0.01259 0.0000034 0.00034 320 320.00 6.9 0.01259 0.0000030 0.00030 340 340.00 6.5 0.01585 0.0000033 0.00033 360 360.00 6.2 0.01585 0.0000030 0.00030 380 380.00 5.9 0.01585 0.0000027 0.00027 400 400.00 5.6 0.01585 0.0000024 0.00024 420 420.00 5.3 0.01585 0.0000022 0.00022 440 440.00 5.1 0.01585 0.0000020 0.00020 460 460.00 4.8 0.01585 0.0000018 0.00018 480 480.00 4.6 0.01585 0.0000017 0.00017 500 500.00 4.5 0.01585 0.0000015 0.00015 IL Near Field (Cylindrical Method) S = (P* KFact) / (27URb) Where: S = power density (mW/cm2) P = total power input to the antenna (mW) K = antenna correction factor / numeric factor for antenna discrimination R = is the straight distance from the antenna to a 6' human being (cm) h = distance between the roof level and the bottom of the antenna (cm) or the vertical distance from the tip of the antenna to the roof level where a 6ft. human being is assumed standing directly from the antenna (R at distance 0) fl.1 Roof level RE Power Density and percent-of-MPE calculations Antenna Array - Verizon Wireless G dist (ft.) R dist (ft.) V angle K factor S (mWkm 2) MPE % 0 5 90.0 0.0010 0.00843 0.49590 1 5.10 78.7 0.0009 0.00737 0.43339 2 5.39 68.2 0.0011 0.00920 0.54096 4 6.40 51.3 0.0025 0.01692 0.99534 S . . 6 7.81 39.8 0.0012 0.00649 0.38168 8 9.43 32.0 0.0005 0.00214 0.12580 10 11.18 26.6 0.0009 0.00352 0.20697 15 15.81 18.4 0.0005 0.00150 0.08818 20 20.62 14.0 0.0002 0.00043 0.02513 25 25.50 11.3 0.000 0.00017 0.00995 30 30.41 9.5 0.0001 0.00014 0.00834 35 35.36 8.1 0.0001 0.00012 0.00718 40 40.31 7.1 0.0001 0.00011 0.00629 45 45.28 6.3 0.0001 0.00012 0.00705 50 50.25 5.7 0.0001 0.00011 0.00636 55 55.23 5.2 0.0002 0.00014 0.00836 60 60.21 4.8 0.0002 0.00013 0.00767 70 7018 4.1 0.0003 0.00015 0.00908 80 80.16 3.6 0.0003 0.00014 0.00795 90 90.14 3.2 0.0005 0.00022 0.01287 100 100.12 2,9 0.0005 0.00020 0.01158 110 110.11 2.6 0.0005 0.00018 0.01053 120 120.10 2.4 0.0006 0.00023 0.01333 140 140.09 2.0 0.0006 0.00019 0.01143 160 160.08 1.8 0.0006 0.00017 0.01000 180 180.07 1.6 0.0006 0.00015 0.00889 200 200.06 1.4 0.0008 0.00016 0.00962 11.2 Roof level RF Power Density and percent-of-MPE calculations Antenna Array - Verizon Microwave Facility G dist (ft.) R dist (ft.) V angle K factor S (mW/cm2) WE % 0 9 90.0 0.00002 0.00000 0.00018 1 9.06 83.7 0.00004 0.00000 0.00036 2 9.22 77.5 0.00006 0.00001 0.00056 4 9.85 66.0 0.00010 0.00001 0.00083 6 10.82 56.3 0.00025 0.00002 0.00190 8 12.04 48.4 0.00063 0.00004 0.00429 10 13.45 42.0 0.00079 0.00005 0.00484 15 17.49 31.0 0.00158 0.00007 0.00742 20 21.93 24.2 0.00251 0.00009 0.00939 25 26.57 19.8 0.00251 0.00008 0.00775 30 31.32 16.7 0.00251 0.00007 0.00657 35 36.14 14.4 0.00398 0.00009 0.00903 40 41.00 12.7 0.00501 0.00010 0.01002 45 45.89 11.3 0.00794 0.00014 0.01418 50 50.80 10.2 0.01000 0.00016 0.01613 55 55.73 9.3 0.01259 0.00019 0.01851 60 60.67 8.5 0.01259 0.00017 0.01700 70 70.58 7.3 0.01585 0.00018 0.01840 80 80.50 6.4 0.01585 0.00016 0.01613 90 90.45 5.7 0.01585 0.00014 0.01436 100 100.40 5.1 0.01585 0.00013 0.01293 110 110.37 4.7 0.01585 0,00012 0.01177 120 120.34 4.3 0.01585 0.00011 0.01079 140 140.29 3.7 0.01585 0.00009 0.00926 I 160 160.25 3.2 0.12589 0.00064 0.06437 S 180 1 180.22 2.9 1 0.12589 1 0.00057 1 0.05724 200 1 200.20 2.61 0.12589 1 0.00051 1 0.05121 Using the data provided by Tetra Tech Wireless, FCC guidelines and other resources, the table above summarizes the results on the ground level computation. The information on the vertical antenna discrimination has been taken from the antenna manufacturer's specification. Also, note that while distances are measured in feet, calculations include/consider the conversion of the units from feet to centimeters, as well as, watt to milliwatt to match and comply with FCC specification of power density and WE. Roof level computation was also considered since this is accessible to the general population. Computation was based on the near field cylindrical method which considers the propagation throughout the entire area of the roof. The energy level was calculated at various points near the antenna up to the edge of the roof. Since the antenna is located/attached at the side of the building, the RF energy emitted towards the rooftop is being partially blocked by the parapet of the building. FCC Policy on Human Exposure to Radio Frequency EMF The FCC is required by the Telecommunication Act of 1996 & National Environment Policy Act of 1969 to evaluate the effect of emission from FCC-regulated transmitter on the quality of the 40 exposureenvironment. At present time there is no federally-mandated radio frequency (RF) exposure standard. However, several non-government organizations, such as the American National Standard Institute (ANSI), the Institute of Electrical and Electronics Engineers, Inc. (IEEE), and the National Council on Radiation Protection and Measurements (NCRP) have issued recommendations for human exposure to RF electromagnetic fields. The potential hazard associated with RF electromagnetic fields is discussed in OET Bulletin No. 56, "Questions and answers about the Biological Effects and Potential Hazards of Radiofrequency Electromagnetic Fields". The commission adopted the NCRP's recommended Maximum Permissible Exposure limits for field strength and power density for the transmitters operating at frequencies of 300 KHz to 100 GHz. In addition, the Commission adopted the specific absorption rate (SAR) limits for devices operating within close proximity to the body as specified within the ANSI/IEEE C95.1-1992 guidelines. Table below lists the FCC limits for both occupational and general population exposures to ,4ifrcnf rrlir iincip' Frequency Range (F) (MHz) Occupational Exposure (MW I cm) General Public Exposure (MW /cm2) 03-1.34 100 100 134-3.0 100 180/F2 3.0-30 900/F2 180/F2 30-300 1.0 _0,2 300-1,500 F/300 1 F/500 . M. 1,500 -100,000 5.0 1.0 Discussion of Safety Criteria : "Ionization" is a process by which electrons are stripped from atoms and molecules. This process can produce molecular changes that can lead to damage in biological tissue, including effects on D A, the genetic material. This process requires interaction with high level of electromagnetic energy. Those types of electromagnetic radiation with enough energy to ionize biological material include X-radiation and gamma radiation. Therefore, x-rays and gamma rays are examples of ionizing radiation. ( ee attachments A&B for additional information) The energy level associated with RF and microwave radiation, on the other hand, are not great enough to cause the ionization of atoms and mo lecules and RF energy is, therefore, is a type of non-ionizing radiation. Other types of non-ionizing radiation include visible light, infrared radiation and other forms of electromagnetic radiation with relatively low frequencies. Often the term "radiation" is used to apply to ionizing radiation such as that associated with nuclear power plants. Ionizing radiation should not confuse with the lower-energy, non-ionizing, radiation with respect to possible biological effects, since the mechanisms of action are quite different. Radiofrequency emissions from antennas used for wireless transmissions such as cellular and PC signals result in exposure levels on the ground that is typically thousands of times less than afety limits. These safety limits were adopted by the FCC based on the recommendations of expert organizations and endorsed by agencies of the Federal Government responsible for health and safety. Therefore, there is no reason to believe that such towers could constitute a potential health hazard to nearby residents or students. Other antennas, such as those used for radio and televi ion broadcast transmissions, use power levels that are generally higher than those used for cellular and PC antennas. Therefore, in some 9 cases there could be a potential for higher levels of exposure on the ground. However, all broadcast stations are required to demonstrate compliance with FCC safety guidelines, and ambient exposures to nearby persons from such stations are typically well below FCC safety limits The FCC does not have the resources or the personnel to routinely monitor the emissions for all the thousands of transmitters that are subject to FCC jurisdiction. However, the FCC does have measurement instrumentation for evaluating RF levels in areas that may be accessible to the public or to workers. If there is evidence for potential non-compliance with FCC exposure guidelines for an FCC-regulated facility, staff from the FCC's Office of Engineering and Technology or the Enforcement Bureau can conduct and investigation, and, if appropriate, perform actual measurements. Remarks and Conclusions: Based on our analysis & computation, the maximum combined power density at this location is 0.00693 mW/cm2 (ground) and 0.01692 mW/cm2 (roof level) of the limit for general population. Therefore, the maximum permissible exposures for the general population on this site are equivalent to 0.40812 % (ground level) and 0.99617 % (roof level) of the recommended limit. The table below will give us individual maximum computed power density and MPE in the roof and ground level for each facility. Carrier Power Density (mW/cm2) Maximum Permissible Exposure (%) Ground Roof Ground Roof Verizon Cell 0.00692 0.01692 0.40717% 0.99534% Verizon jiwave 0.0000107 0.00064 0.00107% 0.06437% The results of this analysis indicate that the maximum level of RF energy to which the public may be exposed is below all applicable health and safety limits. Specifically, in all normally accessible area surrounding the facility, the maximum level of RF energy associated with simultaneous and continuous operation of all proposed transmitters is less than the percentage of the safety criteria adopted by the Federal Communications Commission as mandated by the Telecommunications Act of 1996 and exposure limit of ANSI, IEEE, NCRP, used by the State of California Department of Health and the limits used by all other states that regulate RF exposure. Accordingly, computation yields that Proposed Verizon Wireless cell site in this location is in compliance with the FCC regulations concerning the control of potential RF exposure. Glossary of Terms: 1. Radiofrequency Energy - radiowaves and microwaves are forms of electromagnetic • energy that are collectivity described by the term "radiofrequency" or "RF". RF emission and associated phenomena can be discussed in terms of "energy", "radiation" or "fields". 10 Radiation is defined as the propagation of energy through space in the forms of waves or particles. Electromagnetic "radiation" can be best described as waves of electric and magnetic energy moving together (i.e. radiating) through space. 2. Effective radiated power - the product of the power supplied to the antenna and its gain relative to a half-wave dipole in a given direction. 3. Equivalent Isotropically Radiated Power (EIRP) - the product of the power supplied to the antenna and the antenna gain in a given direction relative to an isotropic antenna 4. Electromagnetic Field (energy density) - the electromagnetic energy contained in an infinitesimal volume divided by that volume 5. Exposure - Exposure occurs whenever and wherever a person is subjected to electric, magnetic or electromagnetic fields other than those originating from physiological processes in the body and other natural phenomena. 6. Gain (of an antenna) - the ratio, usually expressed in decibels, of the power required at the input of a loss-free reference antenna to the power supplied to the input of the given antenna to produce, in a given direction, the same field strength or the same power density at the same distance. Gain may be referenced to an isotropic antenna (dBi) or half-wave dipole (dBd). 7.. General Population / uncontrolled exposure - applies to human exposure to RE fields when the general public is exposed or in which persons who are exposed as a consequence of their employment may not be made fully aware of the potential for exposure or cannot exercise control over their exposure. Therefore, members of the general public always fall under this category when exposure is not employment-related. 8. Maximum Permissible Exposure - the rms and peak electric and magnetic field strength, their squares, or the plane-wave equivalent power densities associated with these fields to which a person may be exposed without harmful effect and with an acceptable safety factor. 9. Occupational I controlled exposure - applies to human exposure to RE fields when persons are exposed as a consequence of their employment and in which those persons who are exposed have been made fully aware of the potential for exposure and can exercise control over their exposure. Occupational/controlled exposure limits also apply where exposure is of a transient nature as a result of incidental passage through a location where exposure levels may be above general population/controlled limits. 10. Power Density (S) - Power per unit area normal to the direction of propagation, usually expressed in units of watts per square meter (W/m 2) or, for convenience, units such as milliwatts per square centimeter (mW/cm) or microwatts per square centimeter (pW/cm). 11. Ionization - a process by which electrons are stripped from atoms and molecules. This process can produce molecular changes that can lead to damage in biological tissue, includes effect on DNA, the genetic material. This process requires interaction with high levels of electromagnetic energy. 12. Non Ionizing radiation - a type of emission which are not great enough to cause ionization of atom and molecules. "RE and Microwave Emissions" are low level energy which are not capable of ionization. . 11 Certification This report was prepared by Expert Wireless Solutions, is issued to Tetra TechWireless as site compliance for the Proposed Verizon Wireless Cellular Facility at 2180 Rutherford Road, Carlsbad, CA 92008. The analysis and computation provided herein were based on applicable FCC regulation concerning safety RF Safety and the control of human exposure to RF field (OET Bulletin 65), additional guidelines and industry practice. The statements and information disclosed in this report are true, complete and consistent with the applicable FCC Rules and Regulations and accepted industry practice. Prepared by: Joel De Torres -RF Engineer Tetra Tech I Expert Wireless Solutions Reviewed by: Charles Neal -Director of Engineering Expert Wireless Solutions A Tetra Tech Company June 17, 2002 June 1 7, 2002 12 9 References: 1. FCC OET Bulletin 65 (Edition 97-01) - Evaluating Compliance with FCC Guidelines for Human Exposure to Radiofrequency Electromagnetic fields. 2. FCC OET Bulletin 56 (Fourth Edition) - Questions and answers about biological effects and potential hazards of RF Electromagnetic fields. 3. 47 CFR, FCC Report and Order (96 326) - Guidelines for Evaluating the environmental Effects of Radiofrequency radiation. 4. Telecommunication Act of 1996, Title VII, Section 704, Facilities Siting; Radio Frequency Emissions Standards 5, National Council on Radiation Protection and Measurements, Bethesda, MD (1986) NCRP Report No. 86 - Biological Effects and Exposure Criteria for Radio Frequency Electromagnetic Fields 6 Institute of Electrical and Electronics Engineers, Piscataway, NJ ANSI/IEEE C95.1-1992 - IEEE Standard for Safety Levels with respect to Human Exposure to Radiofrequency Electromagnetic Fields (3kHz to 300 GHz) 7 American National Standard Institute - Safety Levels with Respect to Human Exposure to Radio Frequency Electromagnetic Fields (3 00 kHz to 100 GHz) ANSI C95.1-1982 8 EMS Wireless - antenna manufacturer 9. A Technical Introduction to Wireless System RF Engineering - Scott Baxter S . 13 Attachments: Electromagnetic Spectrum & Effects The Electromagnetic Spectrum • Electrical Power. Radio waves for Communication, Microwaves, Heatt Visible Light~ Ultraviolet light, X-rays. and Nuclear radiation are all part of the electromagnetic spectrum Frequency, 0 101-,, Hertz 10,s 1017 102a '1024 .o ....-----.----------------, Non-Ionizing and Ionizing Radiation 105 Ftequency. 10u Hertz 1015 1017 Cosmic Rays,, Nuclear ■ ElectromagnetJc anargy at frequencies below vi$ible light is µnon-ionizing'* • the photons don·t contain enough energy to knock electrons out of atoms or molecules, and no chemical changes are caused • the energy turns into heat tf absorbed • the onfy known effects on living things come from this heat • at power levels defined in FCC standards. the heating is not physically perceptible --less than from the light of a flashlight • research is continuing into other possible interaction mechanisms. bl.rt no conclusive Jinks yet seen ■ Electromagnetic energy at frequencies above visible light ts "ionizing,. • photons have enough energy to tear electrons from their atoms, creating ions • can cause chemical and biotogicaf changes (sun tans and more serious effects) Cumulative and Non-Cumulative Radiation Effects. ■ Effects of non➔onizing radiation are not cumulative • heating is the only known mechanism causing effects • heating at allowed levels causes no changes in tissue ■ Effects of ionizing radiation are cumulative • chemical changes: formation of ions which may eventually recombinei or may linger as free radicals with potential biological damage; cells die, and may possibly mutate