INTERNATIONAL FIRE TRAINING CENTRE

Transcription

1 INTERNATIONAL FIRE TRAINING CENTRE RFFS SUPERVISOR INITIAL RADIOACTIVE MATERIALS Areas of information in bold type are considered to be of prime importance. Throughout this note he means he/she and his means his/hers. INTRODUCTION The Aerodrome Fire Service is sometimes called upon to deal with incidents involving hazardous material as part of the overall cover it provides. Some hazardous materials present a risk to the health and safety of passengers and firefighters and to the environment in which we work. If the handling and control of hazardous materials are fully understood and the correct procedure carried out, then the risk is dramatically reduced. AIM To inform RFFS Supervisors of the risks involved and the relevant protective measures/procedures to be used to deal safely with incidents involving radioactive materials. OBJECTIVES Participation in the lesson covering this subject and careful study of this training note will enable RFFS Supervisors to: Briefly explain the term radiation Recognise the hazards associated with radioactive materials State the rules for protection against the effects of radiation Outline the procedures for working safely at incidents with and without monitoring equipment WHAT IS RADIATION To understand radiation we need to look closely at the atomic composition of substances. Figure 1 below shows how an atom of a substance may look under a powerful microscope. IFTC/05/130/39/AVIATION2013/SUPIiLEARN/Page 1 of 13/RADIOACTIVE MATERIALS/ISSUE 1/Jan2013

2 Proton (Positive charge) Neutron (No charge) Electron (Negative charge) The Nucleus of the atom contains protons and neutrons, protons carry a positive electrical charge whereas neutrons have no electrical charge. Orbiting around the nucleus are tiny particles called electrons which carry a negative electrical charge. The atom depicted in Figure 1 would be stable and not giving off radiation because: The nucleus contains an equal number of protons and neutrons (i.e. 2 of each) The atom is electronically balanced because it has the same number of protons and electrons Where a substance has atoms with unequal numbers of protons and neutrons in the nucleus, it is referred to as unstable. It will attempt to change itself in order to achieve a balance. It does this initially be emitting tiny particles of energy known as alpha or beta particles. If this does not achieve the desired balance the residual energy will be given off as electromagnetic rays known as gamma rays. This process, known as radioactive decay, will continue until the substance becomes stable. Alpha Beta Gamma Substances with large numbers of protons and neutrons in the nucleus are more likely to become unstable (see figure 2 above). Uranium is an example. Uranium has 92 protons and over 140 neutrons in its nucleus. A substance that becomes unstable and emits energy in the form of particles or electromagnetic rays in order to achieve a balance is referred to as radioactive. IONISING RADIATION Fig. 2 Radiation is said to be ionising if it has enough energy to ionise atoms, that is, to remove electrons from them. Once an electron has been removed from an atom the atom will no longer be electrically neutral, the detached electron will attach itself to another atom making that atom either positively or negatively charged, and so the process will go on. In order to stabilise itself the atom will emit radioactive energy. In order to stabilise itself the atom will emit radioactive energy. If this energy hits the human body the atoms that make up the cells of the body will be ionised. This can cause a IFTC/05/130/39/AVIATION2013/SUPIiLEARN/Page 2 of 13/RADIOACTIVE MATERIALS/ISSUE 1/Jan2013

3 breakdown of the structure of tissues. Sometimes the tissue will recover, but in other cases, the damage done may be permanent. ALPHA PARTICLES An alpha particle is made up of 2 protons and 2 neutrons bound together. It is therefore positively charged. Because if its relatively high mass and low speed it can only travel a very short distance (30-40mm from source). However this speed/mass/positive charge combination cause alpha particles to produce intense ionisation over a short distance. Alpha particles have very little penetration power and cannot penetrate the skin. Their path can, in fact, be stopped by a sheet of paper. Although protecting the body from alpha particles is fairly easy, the effects can be extremely harmful if alpha emitters are inhaled, swallowed or enter the body through a break in the skin. BETA PARTICLES Beta particles are very small and, are identical to electrons. They can, however, be positively or negatively charged. They have greater penetrating powers than alpha particles which means that without proper protection, they could penetrate the skin and reach sensitive tissues. Beta particles are capable of travelling about 1 metre from source but they can be stopped by layers of heavy clothing e.g. full fire kit. Like alpha particles, they are harmful if permitted to enter the body. GAMMA RAYS Gamma rays are not charged particles like alpha and beta. They are invisible rays of highly energetic, electromagnetic radiation. These rays are capable of travelling several hundred metres from source and are highly penetrating. Owing to this quality they are difficult to provide protection against and so, will penetrate the whole body. Gamma rays can only be stopped, or their energy reduced by very dense materials such as lead or concrete. IFTC/05/130/39/AVIATION2013/SUPIiLEARN/Page 3 of 13/RADIOACTIVE MATERIALS/ISSUE 1/Jan2013

4 SUMMARY TABLE The table below can be used to compare the damage potential, and protection requirements for each type of radiation. Types of Radiation Alpha particles Beta particles Gamma rays Composition Distance it can travel in air before stopping About 30 40mm Can be stopped by 2 protons 2 neutrons A sheet of paper 1 electron About 1 metre Heavy clothing i.e. full fire kit Ray of energy Several hundred metres Dense material such as lead Effect on human body Does not penetrate the skin Can penetrate the skin to reach the sensitive tissues of the body Can penetrate the whole body ABSORBED DOSE Absorbed dose is a term used to describe the amount of radio-active energy that has been absorbed by a body. The SI unit for absorbed dose is the gray. A body is said to have absorbed 1 gray when 1 joule of radioactive energy has been absorbed by each kilogram of that body. For example; if a firefighter weighs 76kg, he/she would have to absorb 76 joules of radioactive energy in order to have an absorbed dose of 1 gray, whereas a firefighter weighing 90kg would have to absorb 90 joules of radioactive energy. In the above example, both firefighters were exposed to an absorbed dose of 1 gray. However, the biological effects on the body may differ according to the type of radiation i.e. alpha/beta/gamma, even though the absorbed doses are equal. For this reason another factor has to be taken into consideration when establishing safe working limits. This other factor is the dose equivalent. DOSE EQUIVALENT To calculate the dose equivalent, we take the absorbed dose (measured in grays) and multiply it by the quality factor of the type of radiation. The quality factor is a comparative figure that takes account of the harmful potential of the type of radiation. The quality factor is as follows: Alpha Particles - Quality Factor = 20 Beta Particles - Quality Factor = 1 Gamma Rays - Quality Factor = 1 The SI unit for dose equivalent is the sievert (Sv). If we apply this to our firefighter weighing 76kg and having absorbed 3 grays, the doses equivalent for beta or gamma radiation would be 3Sv and for alpha radiation it would be 60 Sv. Medical Effects of Radiation The effects of radiation on the human body depends on whether the source of the radiation is inside or outside the body. These are referred to as the internal and external hazards. Other factors affecting the degree of biological damage to the body are: IFTC/05/130/39/AVIATION2013/SUPIiLEARN/Page 4 of 13/RADIOACTIVE MATERIALS/ISSUE 1/Jan2013

5 1 The size if the absorbed dose 2 The period over which the dose is received 3 The type of radiation 4 The sensitivity of the tissues receiving the dose 5 The age of the person 6 Proportion of the body exposed to radiation The following table shows the medical symptoms caused by acute, whole body gamma radiation. Equivalent Dose 6 sieverts or more Medical Symptoms Immediate nausea and vomiting, death of an entire population in 1 to 2 weeks 3 to 6 sieverts Sickness, death in 4 to 6 weeks 4.5 sieverts Half of any population exposed to this dose would die 2 to 3 sieverts Moderate sickness, some recover in 3 months, death after 4 weeks if in poor health 1 to 2 Some nausea and vomiting within 24 hours 0 to 1 sieverts No acute effects, but increasingly serious long term hazards MAXIMUM PERMISSIBLE DOSE LIMITS In the event of a radiation emergency, the principles of the Health and Safety at Work Act should be applied and dose rates should be kept as low as reasonably practicable (ALARP) Dose limitations set out in the Ionising Radiation Regulations 1999 for all occupational workgroups should also be applied. The maximum permissible dose limits for firefighters as a result of the above legislation is: Male firefighters 20mSv in any calendar year Female firefighters of reproductive capacity 13mSv in any consecutive period of three months Female firefighters beyond reproductive capacity dose limits are as per male firefighters. Following any exposure to radiation, health surveillance by a qualified practitioner should take place and records should be maintained for a minimum of 50 years. For more detailed information regarding the above see the Ionising Radiation Regulations IFTC/05/130/39/AVIATION2013/SUPIiLEARN/Page 5 of 13/RADIOACTIVE MATERIALS/ISSUE 1/Jan2013

6 PACKAGING REQUIREMENTS SPECIFIED BY THE INTERNATIONAL AIR TRANSPORT ASSOCIATION The International Air Transport Association (IATA) has laid down regulations covering the transportation by air of radioactive materials. These regulations have been based on the International Atomic Energy Authorities regulation for the safe transportation of radioactive materials. In order to keep this note confined to its practical application it will suffice to say that the regulations are designed to ensure that: 1 Radioactive sources are carried in such a manner that they represent no significant danger to any other materials being carried. 2 The amount of fissile material carried is packed, stored and shipped in such a manner that criticality cannot credibly occur. 3 The amount of radioactive material being carried does not constitute a hazard to the crew or passengers of the aircraft or persons required to handle the material. 4 The radioactive material is indicated in such a way that it is obvious that the package etc contains radioactive material and the strength of any such source is indicated. The regulations also specify such things as package labelling and package strength criteria. It should be noted that the following are NOT ACCEPTABLE for carriage by air: flammable radioactive materials pyrophoric radioactive liquids EACH PACKAGE MUST BE CATEGORISED AND LABELLED Packages and freight containers both large and small must be allotted to one of the following three categories: CATEGORY I - WHITE A package is in category I - white when the radiation level A package is in category I - white when the radiation level originating from the package at any time during normal transport does not exceed 5 Sv/hr at any point on the external surface of the package and the package does not belong to fissile class II or fissile class III and is not being transported under special arrangements. IFTC/05/130/39/AVIATION2013/SUPIiLEARN/Page 6 of 13/RADIOACTIVE MATERIALS/ISSUE 1/Jan2013

7 CATEGORY II - YELLOW A package is in category II - Yellow when the package does not belong to fissile class III, when it is not being transported under special arrangements and the radiation level originating from the package at any time during normal transport does not exceed 500 Sv/hr at any point on the external surface of the package. The Transport Index (TI) can be used to indicate the external radiation hazard associated with the package. It is simply a factor of (10) ten less than the dose in Svh-1 that would be received at 1 metre from the package surface which takes into account the shielding protection that is provided by the packaging. (TI = dose Sv/hour 10) CATEGORY III - YELLOW A package is in category III - Yellow when the radiation levels for category II - Yellow are exceeded, or when the package belongs to fissile class III provided that the radiation level originating from the package at any time during normal transport does not exceed 2 msv/hr per hour at any point on the external surface of the package. The Transport Index (TI) can be used to indicate the external radiation hazard associated with the package. PLEASE NOTE: Actual dimensions of hazard labels are 100 mm x 100 mm It is simply a factor of (10) ten less than the dose in Svh-1 that would be received at 1 metre from the package surface which takes into account the shielding protection that is provided by the packaging. (TI = dose Sv/hour 10) It should be noted that the fact that an aircraft is carrying radioactive material will no way increase the possibility of a fire nor affect its intensity should one occur. PROTECTION FOR CREWS AT RADIATION INCIDENTS It can be seen by the effects of radiation that it is important to ensure that the dose a person receives is kept as low as possible. Damage to the body from radiation may occur from either an external source or an internal source. EXTERNAL SOURCE There are three main rules for protection against external radiation. They are Time, Distance and Shielding. IFTC/05/130/39/AVIATION2013/SUPIiLEARN/Page 7 of 13/RADIOACTIVE MATERIALS/ISSUE 1/Jan2013

8 TIME Limit Exposure Time: The total dose of radiation absorbed by an individual is accumulated in the body over the period of time that the individual is exposed to radiation. Therefore, it follows that the shorter the exposure time, the less the amount of radiation which is absorbed. At any given dose rate and distance from a radioactive source, the amount of radiation absorbed is directly proportional to the period of exposure. i.e. if a person is standing 2 metres from a source and is receiving radiation at a rate of 4 sieverts/hour then the total dose of radiation absorbed in: 2 hours would be 8 sieverts 1 hour would be 4 sieverts 30 minutes would be 2 sieverts 15 minutes would be 1 sievert DISTANCE Keep as far as practically possible from the radioactive source: External radiation falls off rapidly as the distance is increased. The greater the distance the greater the area over which the radiation is spread. The amount of radiation absorbed by an individual over a given period of time is inversely proportional to the distance and decreases according to the inverse square law. This is best explained with the aid of the following diagram: The crossed area represents the area of the body Gamma Source 1m 2m 270 msv 67.5 msv 3m 30 msv IFTC/05/130/39/AVIATION2013/SUPIiLEARN/Page 8 of 13/RADIOACTIVE MATERIALS/ISSUE 1/Jan2013

9 At a distance of 1 metre radiation is received at a rate equivalent to 270 msv/hr. At a distance of 2 metres, the same amount of Gamma radiation energy has spread out and is passing through 4 times the areas as that occurring at 1 metre. This effectively quarters the dose rate experienced in the crossed area. Move away from the source a further 1 metre to 3 metres and the reduction in the amount of radiation affecting each unit of area is considerable. A look at the diagram reveals the fact that each unit of area is receiving only a ninth of the dose rate experienced at 1 metre. This application of the inverse square rule illustrates just how effective the use of distance is in reducing the effects of receiving doses of Gamma radiation. An operational application of this principal can be seen by how quickly a male firefighter will reach his maximum dose limitation at differing distances. At 1 metre, a 270 msv/hr Gamma radiation source will deliver the maximum dose in just 4m 25secs, approximately. Double the distance from the source and the resulting time to limit is increased to 17.7 minutes. Move out to 3 metres and the difference is dramatic. It will now take 40 minutes to reach his limit. The equation to arrive at these figures is as follows: Example: A B = D C Where; A = maximum male firefighter dose limit in msv B = Gamma radiation dose rate in msv/hr C = minutes in an hour D = time in minutes to dose limit SHIELDING Shield the body from the source wherever possible: A firefighter wearing Breathing Apparatus and protective gloves would, under normal circumstances, be protected against alpha and beta radiation. Gamma radiation travels further and can penetrate clothing etc, so it is necessary to consider additional precautions. We know that gamma radiation can only be stopped by being absorbed in dense materials. However, in a practical situation, a firefighter would need to use whatever shielding was available, i.e. brick or concrete walls, etc. The three factors which affect the protection afforded by a material are: 1 The density of the material 2 The layer of the material 3 Radiation type and energy The greater the layer and density of material, the greater the amount of radiation it will absorb. IFTC/05/130/39/AVIATION2013/SUPIiLEARN/Page 9 of 13/RADIOACTIVE MATERIALS/ISSUE 1/Jan2013

10 The following chart shows the thickness of each material that is required to reduce the intensity of gamma radiation by one half (the half value layer). This may vary according to the energy of the incident Gamma radiation, hence a greater HVL may be required to reduce the intensity to one-half. Material Lead Steel Concrete Brick Earth Water Timber Half Value Layer 13mm 18mm 57mm 72mm 85mm 124mm 227mm As the chart shows, approximately 75mm of brick will reduce the intensity of radiation by one half. Therefore a 225mm brick wall (two brick widths) is equal to three half value layers and will reduce the intensity of the radiation to one eighth of the original value. (½ x ½ x ½ = ⅛) It should be remembered that it is more important to protect the trunk and vital organs that the arms and legs. However, radioactive sources should never be picked up with the fingers. INTERNAL SOURCE It is essential that radioactive particles do not enter the body. At an incident involving radioactive materials, it is important to protect the body from as much external radiation as possible, and vital, particularly when radioactive vapours, liquids or powders are involved, to prevent the external hazard from entering the body and becoming an internal' hazard. It is therefore important that we know and understand the rules for: preventing radioactive materials from entering the body protecting the body from external radiation Three Rules for Preventing Radioactive Materials Entering the Body 1 Wear Breathing Apparatus Radioactive materials may be in gas, liquid or powder form and may cover a wide area such as may occur in the case of a road accident. Precautions must be taken to prevent the inhalation of the radioactive materials. 2 Do not eat, drink or smoke Radioactive materials may be picked up on gloves or clothing and enter the body through the mouth and reach vital organs via the digestive system. Personnel should be thoroughly decontaminated and move away from the contaminated area before being allowed to eat, drink or smoke. IFTC/05/130/39/AVIATION2013/SUPIiLEARN/Page 10 of 13/RADIOACTIVE MATERIALS/ISSUE 1/Jan2013

11 3 Withdraw if you sustain open wounds or damage your PPE Radioactive materials may enter the body through open wounds and reach the vital organs of the body via the bloodstream. Anyone sustaining an open wound should withdraw from the contaminated area immediately and wash the injury thoroughly. PROCEDURE AT AN INCIDENT At aerodromes where no protective clothing, Breathing Apparatus or radiation instruments are available and an incident occurs involving radioactive materials, the Local Authority Fire Brigade (LAFB) should be requested to attend immediately. Only essential firefighting should be carried out using the least number of personnel possible. Firefighting should be carried out upwind. Packages and wreckage should not be disturbed other than for the purpose of rescue. The area should be cordoned off and entry restricted. This Instruction/Procedure should be contained in Aerodrome Manuals and emergency instructions. Action prior to the arrival of the LAFB should be confined to carrying out rescue of crew and passengers. The fire situation should be dealt with using the least number of personnel possible. Firefighting should be carried out upwind. Packages and wreckage should not be disturbed other than for the purpose of rescue. At aerodromes where the facilities for dealing with incidents involving radioactive materials exist the officer in charge should ensure that full protective clothing and breathing apparatus are worn. Safe distances and times for the crews should be determined using a survey meter. Before crews enter the radiation area personal dosimeters should be attached to their fire tunics, any reading on the dosimeter prior to entry should be recorded on the reverse side of the breathing apparatus tally. On leaving the area personnel must collect their tallies from the Control Officer and ensure that any increased reading on the dosimeter is recorded on the rear of the breathing apparatus tally. ESTABLISHMENT OF RESTRICTED AREA When the presence of radioactivity is indicated by the survey meter, the officer in charge will determine (because of the strength of the source) whether or not to establish a restricted area. Once it has been decided that a restricted area is necessary, movement in and out of the area must be strictly controlled. The boundary of the restricted area should be clearly marked, preferably with ropes or similar. In normal circumstances it will be the responsibility of the Police to regulate entry and exit of personnel to and from the area. The area should be constantly checked by use of the survey meter, to make sure that the affected area has not spread outside the zone, and that the strength of the source has not increased to dangerous levels. Fire Brigade personnel inside the zone should check regularly the strength of the radiation by use of their dosimeters. Any person whose dosimeter records that they have received a total dose approaching their maximum limit must be withdrawn immediately from the radiation area. Only minimum personnel and equipment should be allowed into the restricted area. If a person becomes a casualty and has to be removed by stretcher it is preferable that ambulance crews should not enter the restricted area, but that they should pass the stretcher over the demarcation line to personnel working inside. IFTC/05/130/39/AVIATION2013/SUPIiLEARN/Page 11 of 13/RADIOACTIVE MATERIALS/ISSUE 1/Jan2013

12 MONITORING EQUIPMENT Personal dosimeters are worn by individuals, they are calibrated in millisieverts to record the total dose of Gamma radiation received by the wearer. Survey meters are calibrated to read in millisieverts per hour. They indicate the level of radiation at any source. Some meters are dual read in microsieverts per hour Contamination meters are calibrated to read in counts per second, beneficial for checking personal contamination and measures the levels of radioactive contamination at the scene. DECONTAMINATION Decontamination of clothing and equipment should be carried out in an area set aside for this purpose. It is important to note, that for the prevention of the spread of radioactive materials during decontamination procedures, that the dose that is received is proportional to the body mass contaminated and that by washing the whole body it is possible to increase the dose received if, for example, the original contamination was confined to the hands. This must be considered and only the areas contaminated washed. In normal circumstances decontamination will consist of the removal of all outer clothing. If there is any question of the body being contaminated thorough washing with soap and water should follow. Checking with a contamination meter is essential both before and after washing. Particular attention should be paid to hair and fingernails. After leaving the restricted area, and when collecting his BA tally, each man must check the reading on his dosimeter against that recorded on is tally. If an increased reading is shown, the BA Control Officer should check the dosimeter reading himself and should make a note of the dose received. Any person who has received a dose of radiation is to be sent to hospital for medical examination. Dosimeters are to be examined to ensure that they have not been contaminated. Radiological experts will normally attend incidents involving radiation and these should be consulted with the officer in charge. Before dis-establishing a decontamination zone, located in a restricted area, the officer in charge should consult with all available experts and relevant agencies. SUMMARY There is no need to be afraid of radiation if you observe the rules. Using the correct instruments it is a case of determining the level of radiation and taking the appropriate precautions. Basically they are, full protective clothing including breathing apparatus; keep time in any active area down to a minimum: keep as far from the source as practical: use shielding to reduce the radiation as appropriate. It should be noted that while the use of chemical protection suits may assist in decontamination they do not provide personal protection against Gamma radiation. The NAIR Scheme Because of the increasing use of radioactive materials the possibility of a mishap also increases. For this reason national arrangements for dealing with incidents involving radiation (the NAIR Scheme) IFTC/05/130/39/AVIATION2013/SUPIiLEARN/Page 12 of 13/RADIOACTIVE MATERIALS/ISSUE 1/Jan2013

13 have been established. Under this scheme experts are available at any time of the day or night and may be called by the police to an incident involving radiation. The scheme has been based on the knowledge that in the majority of cases incidents do not involve fire but are concerned with accidental loss or discovery of radioactive sources, or with damage to radioactive consignments in traffic accidents. If the Police are not already in attendance they should be notified without delay. Unless prior arrangements have already been made to deal with such an incident they will take the necessary steps to activate the NAIR Scheme. IFTC/05/130/39/AVIATION2013/SUPIiLEARN/Page 13 of 13/RADIOACTIVE MATERIALS/ISSUE 1/Jan2013