Notes on Missouri 19 CSR 20-10: Protection Against Ionizing Radiation

19 CSR 20-10.010 Definitions Relating to Ionizing Radiation

Purpose: This rule defines technical terms used throughout the chapter. It also notes incorporation by reference for material filed elsewhere and how to access it.
Key definitions (in order):
- Absorbed dose: energy imparted to matter by ionizing particles per unit mass at the place of interest. Unit: the rad.
- Aluminum equivalent: thickness of aluminum providing the same attenuation under specified conditions as the material in question.
- Controlled area: area where occupational exposure to radiation or radioactive material is supervised by an individual in charge of radiation protection; access, occupancy, and working conditions are controlled for protection.
- Dead-man switch: circuit-closing contact is maintained only with continuous pressure by the operator.
- Department: Missouri Department of Health.
- Dose (rem): rem dose is the unit used in these rules unless otherwise indicated.
- Effective half-life (Teff): Teff = (Tb Tr) / (Tb + T_r) where Tb = biological half-life (days), Tr = physical half-life (days).
- Excessive radiation dose: a dose in excess of the MPD defined in 19 CSR 20-10.040.
- Individual: any human being.
- Installation: a place containing one or more sources of radiation.
- Lead equivalent: thickness of lead providing the same attenuation under specified conditions as the material.
- Maximum permissible accumulated dose (MPAD): dose of radiation which, if accumulated over a lifetime, is not expected to cause observable harm.
- Maximum permissible dose (MPD): maximum rem dose that body or a body part may receive in a stated period.
- Person: includes individuals, partnerships, corporations, trusts, estates, agencies, political subdivisions, and legal successors/representatives.
- Personnel monitoring: determination of radiation dose received by an individual during a specified period.
- Protective barrier: barrier of attenuating material used to reduce radiation exposure.
- Qualified expert: an individual trained/experienced to perform dependable radiation surveys, oversee monitoring, and estimate hazard. The department may judge qualifications, possibly using other experts’ testimony.
- Rad: unit of absorbed dose; 1 rad = 100 ergs per gram.
- Radiation: gamma rays and X-rays, alpha and beta particles, fast electrons, neutrons, protons, other nuclear particles and any other ionizing radiation (not sound, radio waves, or visible/IR/UV light).
- Radiation hazard: condition that might expose individuals to excessive radiation dose.
- Radiation machine: device that produces radiation when operating.
- Radioactive material: material that emits radiation spontaneously.
- Relative biological effectiveness (RBE): numerical factor to compare absorbed dose effectiveness delivered in different ways; standard reference is X-ray/gamma in water with LET 3 keV/µm. Table of RBE values provided in 19 CSR 20-10.110.
- Rem: dose equivalent; absorbed dose in rads multiplied by appropriate RBE.
- Roentgen: unit of exposure; exposure in air that produces ions measured as 1 esu of electricity per 0.001293 g of air.
- Sealed source: radioactive material enclosed to prevent escape.
- Source (of radiation): radiation machine or amount of radioactive material.
- Survey: evaluation of actual or potential radiation or contamination hazards by a qualified expert.
- X-ray tube housing protective diagnostic-type: reduces leakage radiation to a maximum of 0.10 roentgen per hour at 1 m when operating at max current/voltage.
- X-ray tube housing protective therapeutic-type: leakage radiation at 1 m cannot exceed 1 roentgen per hour; at 5 cm from surface, leakage cannot exceed 30 roentgens per hour.
- Useful beam: portion of radiation that passes through window, aperture, cone, or collimating device.
- User: person with administrative control over one or more sources.
- Other terms: defined or interpreted per NCRP, NBS Handbooks, or ANSI Glossary; preference order: NCRP Handbooks > NBS > ANSI.
- AUTHORITY: section 192.420, RSMo 1986; original authority: 192.420, RSMo 1963.

19 CSR 20-10.020 Exemptions from Requirements of this Chapter

Purpose: List exemptions to avoid unnecessary regulation and duplication.
Exemptions include:
- Timepieces, instruments, novelties, or devices containing self-luminous elements themselves. Not exempt if stored/used in a way that could exceed MPD limits in 19 CSR 20-10.040.
- Electrical equipment producing radiation incidental to operation, provided whole-body dose rate at closest approach does not exceed 0.5 rem/year when external shielding is removed (production/testing during factory servicing not exempt).
- Radiation machines that cannot be used to produce radiation (e.g., X-ray machines in storage/transport).
- Radioactive material being transported across state lines in compliance with federal safety regulations.
- Use of radioactive sources licensed by NRC to installations in Missouri.
- Other sources of radiation that the department approves as exempted.
AUTHORITY and history notes (same as Defs).

19 CSR 20-10.030 Registration of Sources of Ionizing Radiation

Purpose: Establish registration requirements for sources of ionizing radiation.
Registration timeline and process:
- Owners/users of non-exempt sources must register within 90 days after the rule’s effective date and every 2 years thereafter; newly acquired sources must be registered within 30 days.
- Registration form describes each source, location, use, waste disposal, and includes names/addresses of users and the qualified expert.
- Notify the department within 30 days of changes that affect exposure potential.
- All nonexempt sources brought into Missouri for temporary use must be registered at least 4 days before entry; may be waived in major urgent occurrences.
- Installations may obtain a registration for research/teaching/production establishments undergoing constant changes; must maintain an active radiation committee and retain a qualified expert with authority to enforce procedures.
- Registration does not imply department approval of conditions.
AUTHORITY: section 192.420, RSMo 1986.

19 CSR 20-10.040 Maximum Permissible Exposure Limits

Purpose: Establish MPD limits for external and internal exposures; includes Table I and conditions for accumulation.
Table I (partial recap): MPD for external exposure for persons in a controlled area
- Whole body, head, trunk: 5 rem/year; 3 rem/quarter (additional allowance under certain conditions).
- Skin of large body area: 30 rem/year; 10 rem/quarter.
- Hands/forearms, feet/ankles: 75 rem/year; 25 rem/quarter.
Conditions for quarterly exception (Col B):
- (A) The quarterly dose of 3 rem is not exceeded;
- (B) Individual’s prior accumulated dose is known;
- (C) The sum does not exceed MPAD: MPAD = (N − 18) × 5 rem, where N is age in full years.
- Note: MPAD sets lifetime dose limits based on age.
Internal exposure controls (Section 2):
- For intake via inhalation, air concentrations must meet Appendix I, Table 2, Col 1 values (workweek assumed to be 40 hours; adjust downward for longer weeks).
- For intake via drinking water/foodstuffs, apply same approach as in section (3).
External exposure outside a controlled area (Section 3):
- MPD to whole body from sources inside the controlled area or escaping radioactive material: 2 mrem in any 1 hour, 0.1 rem in any 7 consecutive days, 0.5 rem in any year.
- Operational factors may be used to meet these limits (e.g., time the area is occupied).
Internal exposure outside a controlled area (Section 4):
- For intake via air, water, or foodstuffs, concentrations in air/food/drinking water must meet Appendix I, Table 2, Columns 2 and 3 values, averaged over a calendar quarter.
AUTHORITY: section 192.420, RSMo 1986.

19 CSR 20-10.050 Personnel Monitoring and Radiation Surveys

Purpose: Set requirements for personnel monitoring and radiation surveys and exemptions.
Monitoring/surveys: Must be performed by or under direction of a qualified expert using suitable instruments and methods.
Interim assessment: If an actual survey isn’t possible yet, a written statement from a qualified expert can serve as evidence of absence of hazard.
When monitoring is required: for each individual with a reasonable possibility of receiving a weekly dose exceeding 50 mrem.
Routine monitoring exemptions (for radiation machines):
- (A) A qualified expert specifies operating conditions under which any individual would not receive more than 25 mrem in any 7 consecutive days or more than 325 mrem in any 13 consecutive weeks.
- (B) The operating conditions are communicated to all potentially exposed individuals.
- (C) The installation continues to operate only under those specified conditions.
Sealed sources/storage areas: Semiannual surveys to ensure containment integrity; capable of detecting 0.005 microcurie of removable contamination.
- If 0.005 µCi or more removable contamination is detected, withdraw the source and decontaminate/repair/dispose per a qualified expert.
AUTHORITY: section 192.420, RSMo 1986.

19 CSR 20-10.060 Radiation Exposure Records and Reports

Purpose: Requires record-keeping for exposures, measurements, and radioactive material handling; reporting exposure incidents.
Records must be kept and available for department inspection; include SSN and date of birth for personnel records.
Radioactive material accounting: Track amount received, transferred, decayed, disposed, and other necessary information; maintain records for at least 5 years after final disposition; include records of releases to the environment.
Termination of employment: Provide a summary of radiation dose to the employee upon request; include circumstances where limits were exceeded.
Employee access: At employee request, provide annual exposure information.
Overexposure reporting: If an accidental dose may exceed 2x the applicable limit, report all facts within 7 days; identify cause and correct it.
Loss/theft reporting: Immediate report by telephone; written report within 24 hours.
Carrier accidents: Any accident involving radioactive material transport must be reported within 24 hours.
AUTHORITY: section 192.420, RSMo 1986.

19 CSR 20-10.070 Storage of Radioactive Materials

Purpose: Safe storage requirements for radioactive materials.
Storage conditions: Materials must be stored to ensure routine access does not expose anyone beyond limits in 19 CSR 20-10.040; plan for emergencies (fire, earthquakes, floods, windstorms).
Ventilation: Vaults/rooms storing gases or airborne particulates must be ventilated so concentrations do not pose a hazard.
Containment: If leakage could occur, provide a secondary tray or catchment to retain the entire amount of material.
AUTHORITY: section 192.420, RSMo 1986.

19 CSR 20-10.080 Control of Radioactive Contamination

Purpose: Limit exposure by controlling/removing contamination.
Work conditions: All work with radioactive materials should minimize spread that could expose anyone beyond limits.
Contamination handling: If clothing or a person can be contaminated, both should be monitored; remove contamination per qualified expert procedures.
Contaminated clothing: Retain inside the installation until decontaminated or disposed of per procedures by a qualified expert.
AUTHORITY: section 192.420, RSMo 1986.

19 CSR 20-10.090 Disposal of Radioactive Wastes

Purpose: Rules for releasing wastes to air/water or disposal by soil burial or sanitary sewer.
Emissions to air/water: No disposal that causes exposure above limits; cooperating users should file pro rata release statements with the Department.
Receiving wastes: Anyone who holds/handles wastes for disposal must obtain a permit from the Department for holding/preparation.
Burial/dumping: Not allowed except at sites approved and registered by the Department.
Sanitary sewer discharge: Allowed if the material is readily soluble, dilution limits are not exceeded by daily releases, and gross quantity does not exceed 1 curie per year.
AUTHORITY: section 192.420, RSMo 1986.

19 CSR 20-10.100 Radiation Labeling

Purpose: Establish labeling and posting requirements for radiation sources, areas, and containers.
(1) Presence of radiation must be posted with signs/labels describing the hazard.
(2) Signs/labels must bear the standard radiation symbol as per Appendix II.
(3) Symbols/signs must only denote radiation hazard and not be used for other purposes.
(4) Signs/labels must use conventional radiation colors: magenta/purple on yellow.
(5) Radiation machines must be labeled: “Caution: Radiation This Equipment Produces Radiation When Energized.” Place near the control panel.
(6) Each area designated as a radiation area with signs if radiation could expose someone at least 5 mrem/hour or 100 mrem in 7 days.
(7) High radiation area (> 100 mR/hr) requires conspicuous signs; internal control circuit to reduce exposure rate or alarm; temporary high-areas may be barricaded instead of circuiting.
(8) Airborne radioactivity areas must be posted; required respiratory protection also indicated.
(9) Rooms/entrances containing radioactive materials must be posted if quantity exceeds 10x the exempted amount per Table 1, Appendix I.
(10) Containers with radioactive material must bear labeling; but labeling exemptions apply if concentration/quantity stay within Table 1/2 limits or for transient laboratory containers.
(11) Areas accessible but not normally occupied with potential hazard should be posted with radiation-hazard labels.
(12) Labels removed when the source is no longer present.
(13) Exceptions:
- (A) Sealed sources not requiring posting if dose rate at 12 inches is below 5 mR/hr and the sealed source is properly labeled.
- (B) Hospitals with patients containing radioactive material may not require posting if attendants are instructed on precautions.
- (C) Signs not required for periods under 24 hours if materials are attended or no one would unknowingly enter.
- (D) Therapeutic X-ray units (≤60 kVp) or diagnostic units may be exempt from posting if precautions prevent exposure to others.
AUTHORITY: section 192.420, RSMo 1986.

19 CSR 20-10.110 Relative Biological Effectiveness Values

Purpose: List RBE values used in other rules; notes that RBE varies with biological effect, acute vs chronic exposure, etc.
Table I — RBE Values:
- X-rays and gamma rays of all energies and electrons and beta rays above 0.03 MeV: RBE = 1.0
- Fast neutrons and protons up to 10 MeV: RBE = 10
- Alpha particles: RBE = 10
- Heavy recoil nuclei: RBE = 20
AUTHORITY: section 192.420, RSMo 1986.

19 CSR 20-10.120 General Requirements for Diagnostic X-ray Equipment

Purpose: General safety requirements for diagnostic X-ray equipment.
(1) X-ray tube housing must be of the protective diagnostic type.
(2) Filtration requirements:
- For equipment ≤ 70 kVp: total filtration in the useful beam, permanently, must be at least 1.5 mm aluminum equivalent. Satisfaction also if HVL ≥ 1.5 mm Al.
- For equipment > 70 kVp: total filtration must be at least 2.5 mm Al; satisfaction if HVL ≥ 2.5 mm Al.
(3) Exposure switch must be dead-man type or time-limiting switch acceptable to the department.
(4) Diaphragms or cones must be used for beam collimation and provide the same protection as the tube housing.
AUTHORITY: section 192.420, RSMo 1986.

19 CSR 20-10.130 Special Requirements for Medical Fluoroscopic Installations

Purpose: Special requirements for medical fluoroscopy.
(1) Fluoroscopes must have primary barriers attenuating the entire cross-section of the useful beam; collimators/shutters to limit beam size to barrier area. For conventional fluoroscopes, margin rule: when the diaphragm is opened fully, at least a 2 cm margin remains unilluminated on the screen at 35 cm from the panel/table top (fourteen inches). If image amplifiers are used, this margin requirement is adjusted; a protective shield required.
(2) Accessory shielding devices (cones, curtains, bucky slot covers) must reduce adjacent dose rate to ≤ 50 mR/hour in the fluoroscopist’s area.
(3) Target-to-panel distance must be ≥ 18 inches.
(4) A manually reset cumulative timing device must be used to indicate elapsed time or shut off after preset exposure; maximum timing range is 5 minutes.
(5) Primary beam barrier lead equivalence varies by kVp:
- 100 kVp: ≥ 2.0 mm lead
- 125 kVp: ≥ 2.4 mm lead
- 150 kVp: ≥ 2.7 mm lead
- If measured exposure-rate at viewing surface does not exceed 50 mR/hour without a patient, under normal operation, this may be considered met for conventional units.
(6) Collimators/shutters must provide at least the specified lead protection according to kVp (2.0/2.4/2.7 mm).
(7) Routine fluoroscopy dose rate at panel/table top shall not exceed 6 R/min.
(8) Mobile fluoroscopic equipment must meet sections (1)–(7) with exceptions: minimum 12-inch target-to-skin distance when no panel; cannot operate unless collimation device in place; the 6 R/min limit applies at the minimum target-to-skin distance.
AUTHORITY: section 192.420, RSMo 1986.

19 CSR 20-10.140 Special Requirements for Medical Radiographic Installations

Purpose: Special requirements for general radiographic X-ray installations.
(1) A device must terminate exposure after a preset time or exposure.
(2) The exposure switch must be arranged so it cannot be conveniently operated from outside a shielded area; spot film devices used with fluoroscopic tables are exempted.
AUTHORITY: section 192.420, RSMo 1986.

19 CSR 20-10.150 Special Requirements for Dental Radiographic Installations

Purpose: Dental radiographic installation requirements.
(1) Useful beam diameter at cone tip must be ≤ 2.75 inches; routine intraoral radiography may allow up to 3 inches.
(2) A device must terminate exposure after a preset time.
(3) Exposure control switch must have a cord long enough to allow operator to stand at least 6 feet from the tube housing and away from the beam.
AUTHORITY: section 192.420, RSMo 1986.

19 CSR 20-10.160 Special Requirements for Mobile Medical Radiographic Installations

Purpose: Special requirements for mobile radiographic units.
(1) Mobile equipment must have cones/frames to ensure minimum target-to-skin distance of at least 18 inches.
(2) Exposure control switch must allow operator to stand at least 6 feet from the patient and outside the primary beam for all exposures.
(3) A device must terminate exposure after a preset time.
AUTHORITY: section 192.420, RSMo 1986.

19 CSR 20-10.170 Special Requirements for Photofluorographic Installations

Purpose: Photofluorographic installation requirements.
(1) A collimator must restrict the useful beam to the fluorographic screen area.
(2) Exposure switch must be arranged so it cannot be conveniently operated outside a shielded area (spot-film devices used with fluoroscopic tables are exempted).
(3) A device must terminate exposure after a preset time or exposure.
(4) Output of the photofluorographic installation shall not exceed 1 roentgen per exposure at the panel.
AUTHORITY: section 192.420, RSMo 1986.

19 CSR 20-10.180 Requirements for Radiation Therapy Installations

Purpose: Rules for radiation therapy setups.
(1) Radiation source housing must be protective therapeutic type.
(2) Permanent diaphragms or cones must be used for collimation; adjustable/removable beam-defining devices must not transmit more than 5% of the useful beam at max KV and with max treatment filter.
(3) Filter system must permit proper filter selection/alignment; filters must be secured to prevent dropping; filter slot should ensure leakage does not exceed 1 R/hour at 1 meter.
(4) Radiation source must be centered and mounted so it cannot turn/slide when on.
(5) Means to immobilize the radiation source during stationary treatment.
(6) A timer to terminate exposure after a preset time.
(7) Interlocks for equipment above 60 kVp: door opening triggers automatic shutoff or reduces room dose to average ≤ 2 mR/hour and max 10 mR/hour at 1 meter; after shutoff, restoration must be possible from the control panel.
(8) Control must be located outside treatment room or in a protective booth.
(9) Shutter-controlled devices must have a shutter position indicator on the control panel.
(10) A clearly visible device on the control panel must indicate whether the ionizing radiation source is on.
AUTHORITY: section 192.420, RSMo 1986.

19 CSR 20-10.190 Requirements for Room Shielding

Purpose: Shielding requirements for diagnostic/therapeutic rooms.
Shielding standards must conform to handbooks published by US Department of Commerce and the National Bureau of Standards.
AUTHORITY: section 192.420, RSMo 1986.

19 CSR 20-10.200 Shoe-Fitting Devices

Purpose: Prohibits use of radiation-based devices for selling footwear.
(1) It is unlawful to operate or maintain any fitting devices or machines within Missouri that use fluoroscopic, X-ray, or radiation principles for selling footwear in commercial outlets.
AUTHORITY: section 192.420, RSMo 1986.
Notes on context and usage:
- The rules collectively aim to minimize radiation exposure to workers and the public, enforce accountability for radioactive materials, ensure proper engineering controls and administrative controls, and promote ALARA (as low as reasonably achievable) principles.
- Several sections reference Appendix I/Table 2 and Table 2/Columns in Appendix I for concentration/dose limits; the exact numeric values are defined in the official appendices (not fully reproduced here).
- Some sections provide exemptions and practical allowances (e.g., temporary postings exemptions, emergency exceptions) to balance safety with operational practicality.
Key formulas to remember:
- Effective half-life: T_ ext{eff} = rac{Tb Tr}{Tb + Tr}
- Maximum permissible accumulated dose: $ext{MPAD} = (N - 18) imes 5\ ext{rem}$ where N is age in full years.
- Relative biological effectiveness (RBE) values (Table I):
- X-rays/gamma/electrons/beta >0.03 MeV: $ext{RBE} = 1.0$
- Fast neutrons and protons up to 10 MeV: $ext{RBE} = 10$
- Alpha particles: $ext{RBE} = 10$
- Heavy recoil nuclei: $ext{RBE} = 20$
Units to be aware of: rem, rad, roentgen (R), millirem (mrem), milliroentgen (mR), curie (Ci).
Connections to broader concepts:
- Systematic protection across medical, industrial, and research settings; emphasis on monitoring, record-keeping, and emergency response.
- Regulatory framework supports transparency, accountability, and continuous improvement in radiation safety.
- Ethical implications include protecting workers and patients, minimizing harm, and balancing access to diagnostic/therapeutic technologies with safety.
Real-world relevance:
- Hospitals and clinics must implement room labeling, shielding, and interlocks; radiology departments maintain exposure records and provide employee dose summaries.
- Facilities handling sealed and unsealed radioactive materials must track inventories and ensure secure storage and disposal.
- Contractors and vendors must comply with exemptions and notification requirements when transporting or bringing in sources for temporary use.