H d t h Physics Vol. 35 (Aug), pp. 381-385 Permon Press Ltd., 1970. Printed in Grcpt Britain @ H d t h Physics S o e i

RADIATION SAFETY STANDARDS FOR BAGGAGE X-RAY EQUIPMENT IN CANADA E W I N and W.M.ZUK Radiation Protection Bureau, Health Protection Branch, Health and Welfare Canada, Ottawa, Ontario, K I A ICI

(Received 6 December 1977; accepted 6 February 1W8)

Abstrrrct-The Radiation Emitting Devices Act of Canada empowers the Federal Government to regulate the safety of radiation emitting devices sold in Canada. This act provides statutory authority for promulgating Regulations on the design, construction and functioning of radiation emitting devices. Standards to control baggage inspection X-ray systems in Canada have been developed and promulgated as Regulations. 2 THE RADIATION EMITTING DEVICES ACT

1. INTRODUCTION

THEINCREASING incidence of aircraft hijackIn 1970 the Canadian federal government ings in the late 1960’s and the early 1970’s passed the Radiation Emitting Devices Act forced civil aviation authorities to introduce (Ra70). thus assuming responsibility for airport security measures designed to protect regulating the safety of radiation emitting against such hijackings. An important devices sold in Canada. The Radiation Emitcomponent of these measures at all major ting Devices Act applies to all devices caCanadian airports was the installation and use pable of emitting electromagnetic radiation of of X-ray equipment for detecting weapons in frequencies greater than 10 MHz or ultrasonic carry-on baggage. A typical unit of the type waves having frequencies greater than 10 kHz. used in Canada is shown in (Fig. 1). In view It excludes nuclear radiation devices because of the popularity of air travel, this measure these fall within the scope of the Atomic gave rise to the possibility of unnecessary Energy Control Act. X-ray exposure to a large fraction of the The most significant aspect of the RadiaCanadian population. tion Emitting Devices Act is that it provides To ensure that the baggage X-ray equip- statutory authority for promulgating regulament did not present a hazard to operators or tions on the design, construction and to the travelling public, the Radiation Protec- functioning of devices and their components tion Bureau, at the request of the federal “for the purpose of protecting persons Ministry of Transport, developed and im- against personal injury, impairment of health plemented stringent safety standards of or death from radiation”. According to the design, construction and performance for Act, no person can import into Canada any such equipment. These standards were in- radiation-emitting device of a class for which itially incorporated into tendering standards have been prescribed, unless the specifications, issued by the Ministry of device and its components comply with the Transport, for the design and development of applicable standards. X-ray units for use in Canadian airports. The 3. mANDARDS FOR BAGGAGE INSPECTION standards were recently promulgated as X-RAY EQUIPMENT Regulations under the Radiation Emitting The proposed safety standards for baggage Devices Act of Canada. 381

382

RADIATION SAFETY STANDARDS

RG.1. Baggage inspection X-ray equipment of the type used at Canadian airports. inspection X-ray equipment were published (Ra74), in the Canada Gazette Part I, in November 1974 for the purposes of soliciting input and comments from manufacturers, users and other interested parties. After review of comments received, final standards were promulgated, as Regulations under the Radiation Emitting Devices Act, and were published (Ra76) in the Canada Gazette, Part XI in February 1976. The regulations came into effect in October 1976.

The Canadian Regulations incorporate specific requirements concerning the basic design of baggage X-ray equipment, the way in which such equipment is to be constructed, and the limits on maximum X-ray leakage levels under normal operating conditions. These Regulations are unique in the world, and great interest in their detailed contents has been expressed by many countries which are in the process of developing similar safety standards.

E. RABIN and W. M. ZUK

383

ally positioned warning lights, or other indicators, are required to indicate when the equipment is powered and when the X-ray beam i s on. For pulsed X-ray systems, the X-rays “ON” light or indicator must remain on for at least onehalf second. Furthermore, such warning lights or indicators must either have builtin redundancy or else be interlocked so To assist others who may also be so inthat if they burn out or malfunction, Xvolved the main features addressed by the rays cannot be generated. Regulations are summarized in Table 1, and 5 . To secure unattended equipment against are described in the remainder of this section. unauthorized use, a key lock switch must be incorporated. The switch must be of a type where the presence of the key in the 3.1 Standards of design and construction switch is required before X-rays can be These standards are prefaced by the generated and where removal of the key general requirement that: (a) the equipment prevents X-rays from being generated. incorporate sufficient shielding to enable compliance with the standards of functioning 6. Much of the commercially available baggage X-ray equipment is modular for set out in the Regulations; and (b) the design ease of mobility. To ensure that the X-ray and construction be such that the standards beam is directed toward the image recepof functioning are met for as long as the tor of the equipment, the X-ray generator equipment has its original components or has is required to align automatically with the replacement components recommended by image receptor when the equipment is the manufacturer. assembled. The specific safety features that must be incorporated in all baggage X-ray units sold 7. A control or controls to initiate the generation of X-rays, and requiring in Canada are as follows: separate operator action for each exposure, must be provided on all baggage 1. All access openings designed for the inX-ray equipment except that equipped sertion or removal of baggage must be with a conveyor system and in which the covered by doors or panels, unless the X-ray exposures are initiated automaticdesign of the unit is such that it precludes the insertion of any part of the human ally by a photocell or other baggage sensing device. For such equipment the body into the primary X-ray beam, requirement is for a control or switch through the openings. requiring continuous pressure by the 2. All such doors or panels must be interoperator to maintain automatic operation locked with not less than two independent and which when released stops the consafety interlocks so that if any of these veyor and terminates X-ray production. A doors or panels are opened when the Xray beam is on, X-ray production is further requirement is that the conveyor terminated. be of sufficient length to prevent insertion of any part of the human body into any 3. All other doors or panels that allow access area where the exposure to X-rays exto areas where the exposure to X-rays ceeds the level specified in the standards may exceed the levels specified in the of functioning. standards of functioning, must be interlocked so that if the doors or panels are 8. To draw attention to the fact that the equipment generates hazardous radiation, opened or removed, X-rays cannot be the X-radiation warning sign (Rp75) shown generated. in (Fig. 2) must be displayed at all access 4. To ensure that the operator and bystanopenings through which baggage is inders are aware when the equipment is on serted or removed. and X-rays are being produced, strategic-

RADIATION SAFETY STANDARDS

384

to the operator is much less than the 1OOOmRlyr since the operator is normally at least a meter away from any external surface of the equipment. L n The potential dose to the travelling public is several orders of magnitude less, as the passengers are in the vicinity of the baggage X-rays units for short periods of time and infrequently, and never approach the units as closely as the operators. Measurements of X-ray leakage levels from units installed at Canadian airports generally indicate levels well below the maximum permitted of 0.5 mR/hr at 5 cm. A FIG. 2. The warning skn used in Canada to intypical set of results is shown in (Fig. 3). dicate the presence of a hazard from X-radiation. With the measured leakage levels taken into consideration, rather than the maximum An additional requirement of this part of permitted level, and taking into account the the Regulations is that the equipment be fact that an operator rarely stands as close as labelled to identify the name and address 5cm to the unit, the actual exposure rate to of the manufacturer, and the model the operator is most unlikely to exceed designation, serial number and date of 10 mR/yr, or 1/10 the “natural background” yearly dose. manufacture of the equipment. 1

-

3.2 Standard of functioning The standard of functioning specified in the Regulations is concerned only with the radiation safety of baggage X-ray equipment and is exprtssed in terms of the maximum permissible leakage rate at the maximum possible baggage handling rate of the equipment. The requirement is that at no point 5 cm distant from any accessible external surface of the equipment must the average exposure rate of X-rays exceed 0.5 mR/hr. For purposes of determining compliance a detection cross sectional area of 10cm2 and an averaging time of 5 min are specified.

5. COMPLIANCE INSPECTION

In addition to being instrumental in the development of the safety standards for

4. CONSEQUENCES OF TEE RADIATION LEAKAGE mANDARD

Assuming a 40-hr work week and 50 work weeks solidus, under the worst case situation in which the operator is physically in contact with the surface of the X-ray equipment, the 0.5 mR/hr level permits a potential exposure to the operator of 1OOOmRlyr. This is 1/5 of the maximum permissible yearly dose to the radiation worker, as recommended by the International Commission on Radiological Protection. In actual fact, the potential dose

FIG. 3. Measured X-ray leakage levels obtained by operating the units in fluoroscopic mode for a time equivalent to 1 hr of pulsed mode operation at the maximum baggage handling rate. The values in parentheses correspond to typical leakage levels; the others are the maximum leakage levels observed in one particular unit.

E. RABIN and W. M. ZUK

baggage X-ray equipment, the Radiation Protection Bureau is also responsible for ensuring compliance of this equipment with the standards. The Bureau carries out a program of inspection and evaluation at points of manufacture of new equipment prior to its introduction for use in Canada. The Bureau also conducts regular inspections of operational units at Canadian airports, and in instances where radiation in excess of the maximum permitted is detected, the responsible user is so advised and appropriate remedial action is instituted immediately. To date, our inspectors have encountered only one operational unit for which X-radiation leakage levels in excess of 0.5 mR/hr were detected. The details of the measurements for this particular unit are given in (Fig. 3). For this unit, the maximum leakage level of 22 mR/hr was detected. It was found to be due to a fault in the lead shielding inside the X-ray tower and was rectified by the addition of 1.6 mm thick lead sheet over the fault area. With this modification, there was no detectable leakage. M)R FILM SAFETY To ensure that the baggage X-ray units at Canadian airports do not fog undeveloped photographic film, the Ministry of Transport has added an additional performance requirement. A maximum exposure per pulse 6. CRITERIA

385

(i.e. per bag inspected) of 0.35 mR has been set for the direct beam. With this exposure there is no detectable (NF74) fogging of standard photographic films. Routine inspections for the operational baggage X-ray units in Canada indicate average direct beam exposures of 0.25-0.30 mRlpulse. 7. SUMMARY

As a direct result of the safety standards developed and implemented by the Radiation Protection Bureau, baggage inspection X-ray units in use in Canada present no radiation hazard to either the travelling public or the operators. REFERENCES

NF74 National Film Board of Canada, 1974, Airport X-ray Inspection of Luggage-Will It Fog My Film?, The Educational Technology Branch Test Report P-2 Ra70 Radiation Emitting Devices Act, 1970, Revised Srarutes of Canada. 1970, Chapter 34 (1st Supplement) (Ottawa: Queen’s Printer for Canada) Ra74 Radiation Emitting Devices Regulations, 1974, “Baggage Inspection X-ray Devices”, Canada Gazette Part I, Vol. 108, No. 44 (Ottawa: Queen’s Printer for Canada) Ra76 Radiation Emitting Devices”, Canada Gazette, Part 11. Vol. 110, No. 4, SOR/76-106 (Ottawa: Queen’s Printer for Canada). Rp75 Repacholi M. H., Ghosh S. K., Lecuyer D. W. and Zuk W. M., 1975, Health Phys. 28, 814.

Radiation safety standards for baggage x-ray equipment in Canada.

H d t h Physics Vol. 35 (Aug), pp. 381-385 Permon Press Ltd., 1970. Printed in Grcpt Britain @ H d t h Physics S o e i RADIATION SAFETY STANDARDS FOR...
155KB Sizes 0 Downloads 0 Views