Hazardous Chemicals Handbook 2 Episode 11 docx

Generally, sampling of waterways should be at the fastest flowing part of the stream/river, usually mid-depth unless the contaminant is less dense than water and could float, or is more dense and could accumulate near the river bed. For lakes representative samples should be taken near to the inflow, outflow and other locations. If two phases are present both may require sampling. Sample preservation by refrigeration, pH adjustment, elimination of light, filtration, and extraction may be important. Table 10.34 summarizes the information to be recorded during an investigation. (A code of practice for the identification of potentially contaminated land and its investigation is given in British Standard DD 175/1988.) Consideration should be given to the application of appropriate quality control and quality assurance procedures such as those advocated by ‘good laboratory practice’ or ISO 17025 to ensure the sampling, the analysis and interpretation/reporting of data are robust since results will dictate action and may be subject to scrutiny by third parties. Duplicate samples may need to be retained for disclosure to third parties. There may be legal requirements to notify results to relevant authorities. POLLUTION MONITORING STRATEGIES IN INCIDENT INVESTIGATION 389 11 Radioactive chemicals The main chemical elements are listed in Chapter 18. Each comprises a nucleus of positively- charged protons and neutral neutrons orbited by negative electrons. The mass number A is given by A = Z + N where Z is the number of protons, or atomic number N is the number of neutrons. Atoms with the same value of Z but different values of A are isotopes (Table 11.1). Many isotopes are stable but others are naturally or artificially radioactive, i.e. their atomic nuclei disintegrate, emitting particles or radiation. This changes the nuclear structure of the atom and often results in the production of a different element. Table 11.1 Nuclear composition of selected istopes Element Symbol Atomic Protons Neutrons Total number Atomic number of protons weight and neutrons Hydrogen 1 1 H 1 1 1 1.0080 (Deuterium) 1 2 H 1112 Carbon 6 12 C 6 6 6 12 12.010 6 13 C 66713 6 14 C 66814 Nitrogen 7 13 N 7 7 6 13 14.008 7 14 N 77714 7 15 N 77815 Chlorine 17 35 Cl 17 17 18 35 35.457 17 37 Cl 17 17 20 37 Lead 82 206 Pb 82 82 124 206 207.21 82 207 Pb 82 82 125 207 82 208 Pb 82 82 126 208 Uranium 92 234 U 92 92 142 234 238.07 92 235 U 92 92 143 235 92 238 U 92 92 146 238 Natural sources of ionizing radiation include cosmic rays and nucleides such as potassium-40, carbon-14 and isotopes of thorium and uranium which are present in rocks, earth and building materials. Industrial sources of radiation include nuclear reactors, X-ray radiography, electron microscopy, X-ray diffractors, thickness gauges, smoke detectors, electron beam welding and certain processes including chemical analysis, polymer curing, chemical/biological tracing, food and medical sterilization, and mining. The radiation source can be sealed, when the radiation can be switched off, or unsealed. Examples of the former are smoke detectors and electrical devices for producing radiation. Hazards The chemistry, and hence hazards, of ‘hot’, or radioactive, elements parallel those of their ‘cold’ isotopes. However, the radiation poses additional toxicity hazards. A qualitative classification of selected isotopes in terms of toxicity is given in Table 11.2. The biological effects of ionizing radiation stem mainly from damage to individual cells following ionization of the water content. Oxidizing species, e.g. hydrogen peroxide, form together with ions and free radicals, all capable of chemical attack on important organic moieties within the cells, e.g. nucleic acids. Biological effects are influenced by the type of radiation, the dose, duration of exposure, exposed organ and route of entry. Effects on cells include death, mutation and delayed reproduction. Acute adverse effects of exposure are illustrated in Table 11.3. Table 11.2 Classification of isotopes according to relative radiotoxicity per unit activity The isotopes in each class are listed in order of increasing atomic number Very high toxicity Sr-90 + Y-90, *Pb-210 + Bi-210 (Ra D + E), Po-210, At-211, Ra-226 + 55 per cent *daughter products, Ac-227, *U-233, Pu-239, *Am-241, Cm-242. High toxicity Ca-45, *Fe-59, Sr-89, Y-91, Ru-106 + *Rh-106, *I-131, *Ba-140 + La-140, Ce-144 + *Pr-144, Sm- 151, *Eu-154, *Tm-170, *Th-234 + *Pa-234, *natural uranium. Moderate toxicity *Na-22, *Na-24, P-32, S-35, Cl-36, *K-42, *Sc-46, Sc-47, *Sc-48, *V-48, *Mn-52, *Mn-54, *Mn- 56, Fe-55, *Co-58, *Co-60, Ni-59, *Cu-64, *Zn-65, *Ga-72, *As-74, *As-76, *Br-82, *Rb-86, *Zr-95 + *Nb-95, *Nb-95, *Mo-99, Tc-98, *Rh-105, Pd-103 + Rh-103, *Ag-105, Ag-111, Cd- 109 + *Ag-109, *Sn-113, *Te-127, *Te-129, *I-132, Cs-137 + *Ba-137, *La-140, Pr-143, Pm- 147, *Ho-166, *Lu-177, *Ta-182, *W-181, *Re-183, *Ir-190, *Ir-192, Pt-191, *Pt-193, *Au- 196, *Au-198, *Au-199, Tl-200, Tl-202, Tl-204, *Pb-203. Slight toxicity H-3, *Be-7, C-14, F-18, *Cr-51, Ge-71, *Tl-201. *Gamma-emitter. Types of radiation The nature of the radioactive decay is characteristic of the element; it can be used to ‘fingerprint’ the substance. Decay continues until both the original element and its daughter isotopes are non- radioactive. The half-life, i.e. the time taken for half of an element’s atoms to become non- radioactive, varies from millions of years for some elements to fractions of a second for others. 1. α-Particles (helium nuclei, i.e. 2 neutrons plus 2 protons): on emission the original isotope degrades into an element of two atomic numbers or less, e.g. uranium 238 produces thorium 234. Such transformations are usually accompanied by γ-radiation or X-radiation. α-Particles have a velocity about one-tenth that of light with a range in air of 3–9 cm. Because of their relatively TYPES OF RADIATION 391 392 RADIOACTIVE CHEMICALS large size and double positive charge they do not penetrate matter very readily and are stopped by paper, cellophane, aluminium foil and even skin. If inhaled or ingested, however, absorption of α- particles within tissues may cause intense local ionization. 2. β-Rays comprise electrons of velocity approaching that of light with a range of several metres and an energy of 0–4 MeV. β-Particles of <0.07 MeV do not penetrate the epidermis whereas those >2.5 MeV penetrate 1–2 cm of soft tissue. Thus β-emitters pose both an internal and an external radiation hazard: skin burns and malignancies can result. Once inside the body they are extremely hazardous, though less so than γ-rays. About 1 mm of aluminium is needed to stop these particles. Most β-emissions are accompanied by γ- or X-radiation and result in transformation into the element of one atomic number higher or lower but with the same atomic mass. 3. γ-Radiation is similar to, but shorter in wavelength than, X-rays and is associated with many α- or β-radiations. γ-Radiation does not transform isotopes/elements. Like X-rays, γ-rays are very penetrating; they are capable of penetrating the whole body and thus require heavy shielding, e.g. γ-rays from 60 Co penetrate 15 cm steel. 4. X-Radiation like γ-radiation is electromagnetic in nature. It can be emitted when β-particles react with atoms. More often it is electrically generated by accelerating electrons in a vacuum tube. The latter source can be switched off. X-rays are extremely penetrating and are merely attenuated by distance and shielding. 5. Neutron radiation is emitted in fission and generally not spontaneously, although a few heavy radionucleides, e.g. plutonium, undergo spontaneous fission. More often it results from bombarding beryllium atoms with an α-emitter. Neutron radiation decays into protons and electrons with a half-life of about 12 min and is extremely penetrating. The same type of radiation emitted by different isotopes may differ significantly in energy, e.g. γ-radiation from potassium-42 has about four times the energy of γ-radiation from gold-198. Units of radiation are the becquerel (Bq), the gray (Gy) and the sievert (Sv). Control measures The control of ionizing radiation is heavily regulated. Expert advice should be sought prior to introducing sources of radiation onto the premises. The general provisos for their control are that: • All practices resulting in exposure shall be justified by the advantages produced. • All exposures shall be as low as reasonably practicable. Table 11.3 Effects of acute exposures to X- and γ-radiation Dose Effects (Gy) <1 No clinical effects but small depletions in normal white cells count and in platelets likely within 2 days. 1 About 15% of those exposed show symptoms of loss of appetite, nausea, vomiting, fatigue etc. 1 Gy delivered to whole body or 5 Gy delivered to bone marrow produces leukaemia. 2 Some fatalities occur. 3.5–4 LD 50 (see Ch. 5), death occurring within 30 days. Erythema (reddening of skin) within 3 weeks. 7–10 LD 100 , death occurring within 10 days. • The dose received shall not exceed specified limits. As with most hygiene standards these limits vary slightly between nations: local values should be consulted. Limits set within the UK are summarized in Table 11.4. • All regulatory requirements will be followed. • All incidents will be investigated and reported. Table 11.4 UK exposure limits (the Ionizing Radiations Regulations, 1999) Dose (mSv in any Employee aged 18 or Trainee under 18 All others calendar year) over Whole body 20* 6 1 Equivalent dose for the Lens of eye 150 50 15 Skin** 500 150 50 Arms, forearms, feet, ankles 500 150 50 Abdomen of women of child bearing 13*** capacity at work (in any consecutive period of 3 months) * Where these limits are impracticable having regard to the nature of the work the employer may apply a dose limit of 100 mSv in any period of 5 consecutive months subject to a maximum effective dose of 50 mSv in any single calendar year, and to prior approval by the Radiation Protection Adviser, the affected employee(s), and the Health and Safety Executive. ** As applied to the dose averaged over an area of 1 cm 2 regardless of area exposed. *** Once an employer has been informed that an employee is pregnant the equivalent dose to a foetus should not exceed 1 mSv during the remainder of the pregnancy and significant bodily contamination of breast-feeding employees must be prevented. In the UK, annual doses of 20 mSv, or any case of suspected overexposure, must be investigated, reported and recorded. The HSE must also be notified of any spillages of radioactive substance beyond specified amounts. Companies are obliged to monitor exposures and investigate excursions beyond action limits, and to maintain records for specified periods. Checks on surface contamination are aimed at avoiding exposure, preventing spread of contaminant, detecting failures in containment or departures from good practice, and providing data for planning further monitoring programmes. Air monitoring will be required, e.g., when volatiles are handled in quantity, where use of radioactive isotopes has led to unacceptable workplace contamination, when processing plutonium or other transuranic elements, when handling unsealed sources in hospitals in therapeutic amounts, and in the use of ‘hot’ cells/reactors and critical facilities. Routine monitoring of skin, notably the hands, may be required. Monitoring for both external and internal radiation may be required, e.g. when handling large quantities of volatile ‘hot’ chemicals or in the commercial manufacture of radionucleides, in natural and enriched uranium processes, in the processing of plutonium or other transuranic elements, and in uranium milling and refining. The nature of biological monitoring is influenced by the isotope: e.g., faeces, urine and breath monitoring is used for α- and β-emitters and whole- body monitoring for γ-sources. Exposure is minimized by choice of source, by duration of exposure, by distance from source (at 1 m the radiation level is reduced almost 10-fold), and by shielding. The greater the mass per unit area of shield material the greater the shielding efficiency. Whereas α- and β-particles pose few problems (the former can be absorbed by, e.g., paper and the latter by 1 cm Perspex) γ- and X-rays are not completely absorbed by shield material but attenuated exponentially such that radiation emerging from the shield is given by: CONTROL MEASURES 393 394 RADIOACTIVE CHEMICALS D t = D 0 e –ut where D 0 is the dose without a shield D t is the dose rate emerging from a shield of thickness t u is the linear absorption coefficient of shield material. Half-thickness values (H-TV) i.e. thickness to reduce intensity to half the incidence value, for materials commonly used as shields for selected γ-rays are exemplified by Table 11.5. Table 11.5 Approximate half-thickness values for a selection of shield materials and γ-emitters Nucleide Half-life γ -energy H-TV (cm) (MeV) Concrete Steel Lead 137 Cs 27 years 0.66 4.82 1.63 0.65 60 Co 5.24 years 1.17–1.33 6.68 2.08 1.20 198 Au 2.7 days 0.41 4.06 – 0.33 192 Ir 74 days 0.13–1.06 4.32 1.27 0.60 226 Ra 1622 years 0.047–2.4 6.86 2.24 1.66 Table 11.6 General control measures for work with radioactive substances Consult experts including competent authorities (in UK the HSE must be given 28 days prior notice of specified work with ionizing radiation). Conduct a risk assessment to any employee and other persons to identify measures needed to restrict exposure to ionizing radiation and to assess magnitude of risk including identifiable accidents. Conduct work in designated controlled areas (e.g. in UK these are areas in which instantaneous dose rates >7.5 µSv/hour occur, or where employees may exceed 6 mSv annual dose limit, or where air concentration or surface contamination exceeds specified levels). Provide barriers for identification and display of appropriate warning notices, e.g. Trefoil symbol. Control exposures by engineering techniques, e.g. containment, shielding, ventilation (consider need for in-duct filters to remove contamination prior to exhausting to atmosphere), backed up by systems of work and personal protection including approved respirators where necessary. Use remote handling techniques where necessary. Appoint a Radiation Protection Adviser: all staff involved with radioactive work should be adequately trained and instructed. Limit access to designated areas to classified persons (e.g. in UK persons likely to receive doses in excess of 6 mSv per year or an equivalent dose which exceeds 30% of relevant hygiene standard). Access may need to be limited by trapped keys or interlocks for high dose rate enclosures. Prepare as appropriate written rules for work in designated areas and appoint Radiation Protection Supervisors. Check exposures routinely by personal dosimetry or following accidents (in the UK dosimetry services must be approved) and keep records (e.g. in UK for at least 50 years). Notify the relevant employees and authorities as appropriate. Monitor background contamination periodically using equipment that has been checked by qualified persons and keep records of levels (e.g. for 2 years). Investigate accidents which may have led to persons receiving effective doses in excess of 6 mSv or an equivalent dose greater than 30% of any relevant dose limit. Investigate and report to the authorities loss of materials from accidental release to atmosphere, spillages, theft. The Regulations provide a comprehensive list of notifiable concentrations for each radionuclide isotope. Provide mandatory medical surveillance for classified workers, e.g. medical examinations prior to commencement of radioactive work followed by check-ups annually or when overexposure may have occurred. (In the UK the surveillance must be undertaken by appointed doctors and records retained for at least 50 years.) Maintain high standards of personal hygiene and housekeeping. Detailed precautions for handling radioactive substances will be dictated by the nature and quantity of isotope and the likely level of exposure. Thus for some materials laboratory coats and gloves may be adequate; for others a fully enclosed suit and respirator may be more appropriate. Some general precautions are listed in Table 11.6. Do not eat, drink, smoke, apply cosmetics or use mouth pipettes in controlled areas. Dress any wounds prior to entering the area. Wherever practicable, store radioactive substances in sealed, properly labelled containers. Check for leaks periodically (e.g. 2-yearly intervals) and maintain records of stocks including sealed sources (e.g. for 2 years). Carry out work over spill trays to contain leakages and use impervious work surfaces. Decontaminate apparatus and prevent cross-contamination. Collect waste for treatment or disposal and deal with spillages immediately. Remove protective clothing in a changing area provided with wash basin, and lockers for clean and dirty clothing. Table 11.6 Cont’d CONTROL MEASURES 395 12 Safety by design Plant and equipment design are regulated by substantial legislation. In the UK this includes: The Health and Safety at Work etc. Act 1974, the Provision and Use of Work Equipment Regulations 1998, the Control of Substances Hazardous to Health Regulations 1999, the Factories Act 1961, the Electricity at Work Regulations 1989, the Fire Precautions Act 1971, together with specific legislation, e.g. the Highly Flammable Liquids and LPG Regulations 1972. Common matters, e.g. ventilation, temperature and lighting; floor, wall and ceiling surfaces; workspace allocation; workstation design and arrangement; floors and traffic routes; safeguards against falls or being struck by a falling object; glazing; doors and gates; travelators and escalators; sanitary and washing facilities; drinking water supply; accommodation for clothing; facilities for changing, resting and meals; are all covered by the Workplace (Health, Safety and Welfare Regulations) 1992. Design procedures To ensure safety consult flowsheets/engineering line diagrams and consider both the materials (raw materials storage, processing, product storage, disposal and transportation) and the process details (scale, batch vs continuous, temperature, pressure, materials of construction, monitoring, safety features, e.g. fail-safe or ‘second chance’ design). See Table 12.1. Subject the proposals to detailed scrutiny, as in Table 12.2 or using a HAZOP study, fault tree analysis, etc. for both the planned operation and anticipated major deviations from normal operation (Table 12.3). A HAZOP (Hazard and Operability Study) involves a formal review of process and instrumentation diagrams by a specialist team using a structured technique, based upon key words. These comprise ‘property words’ and ‘guide words’, e.g. as in Table 12.4. Where possible plants of intrinsically safe design are preferred, i.e. those which have been designed to be ‘self-correcting’ rather than those where equipment has been ‘added on’ to control hazards. Some characteristics of intrinsically safe plants are: • Low inventory (small plant with less inherently hazardous materials on site). • Substitution of hazardous materials with less dangerous chemicals. • Attenuation of risk by using hazardous materials in the least dangerous form. • Simplification of plant, instrumentation, operating procedures to reduce the chance of human error. • Domino effects eliminated so that adverse events are self-terminated and do not initiate new events. • Incorrect assembly of plant made impossible by equipment design. Table 12.1 Some considerations in reaction process selection and design Are unstable reactions and side reactions possible, e.g. spontaneous combustion or polymerization? Could poor mixing or inefficient distribution of reactants and heat sources result in undesirable side reactions, hot spots, runaway reactions, fouling, etc? Can hazards from the reaction be reduced by changing the relative concentration of reactants or other operating conditions? Can side reactions produce toxic or explosive material, or cause dangerous fouling? Will materials absorb moisture from the air and then swell, adhere to surfaces, form toxic or corrosive liquid or gas, etc? What is the effect of impurities on chemical reactions and upon process mixture characteristics? Are materials of construction compatible mutually and with process materials? Can dangerous materials build up in the process, e.g. traces of combustible and non-condensible materials? What are the effects of catalyst behaviour, e.g. aging, poisoning, disintegration, activation, regeneration? Are inherently hazardous operations involved: Vaporization and diffusion of flammable/toxic liquids or gases? Dusting and dispersion of combustible/toxic solids? Spraying, misting or fogging of flammable/combustible materials or strong oxidizing agents? Mixing of flammable materials and combustible solids with strong oxidizing agents? Separation of hazardous chemicals from inerts or diluents? Increase in temperature and/or pressure of unstable liquids? • The status of plant should be immediately obvious. • The tolerance should be such that small mistakes do not lead to major problems. • Leaks should be small. Table 12.5 summarizes the application of these principles (after Kletz – see Bibliography). Where this approach is not feasible, external features of plant must ensure the minimization of unwanted consequences. Layout Factory layout has a significant bearing on safety. Relevant considerations include: • Relative positions of storage and process areas; control room, laboratories and offices – i.e. areas of highest population density; switch-house; materials receipt and despatch areas; effluent treatment facilities. Spacing distances according to standard guidelines. • Need for normal and emergency access (and escape). • Security, e.g. fencing requirement, control of access. • Topography. • Tendency for flooding. • Location of public roads. • Prevailing wind direction. • Zoning of electrical equipment (Table 12.6). • Positions of neighbouring developments, housing, public roads, controlled water courses, etc. Segregation is practised to allow for housekeeping, construction and maintenance requirements and to reduce the risk of an accident resulting in a ‘domino effect’, e.g. from a fire, explosion or toxic release. For very toxic substances, e.g. prussic acid (HCN) or tetraethyl lead, this may involve isolating the entire manufacturing operation in a separate unoccupied building or sealed- off area. LAYOUT 397 398 SAFETY BY DESIGN Table 12.2 Chemical process hazard identification Materials and reaction Identify all hazardous process materials, intermediates and wastes Produce material information sheets for each process material Check the toxicity of process materials, identify short and long term effects for various modes of entry into the body and different exposure tolerance Identify the relationship between odour and toxicity for all process materials Determine the means for industrial hygiene recognition, evaluation and control Determine relevant physical properties of process materials under all process conditions, check source and reliability of data Determine the quantities and physical states of material at each stage of production, handling and storage, relate these to the danger and second-degree hazards Identify any hazard the product might present to transporters and public while in transit Consult process material supplier regarding properties, characteristics, safety in storage, handling and use Identify all possible chemical reactions, both planned and unplanned Determine the inter-dependence of reaction rate and variables, establish the limiting values to prevent undesirable reactions, excessive heat development etc. Ensure that unstable chemicals are handled so as to minimize their exposure to heat, pressure, shock and friction Are the construction materials compatible with each other and with the chemical process materials, under all foreseeable conditions? Can hazardous materials build-up in the process, e.g. traces of combustible and noncondensible materials? General process Are the scale, type and integration of the process correct, bearing in mind the safety and specification health hazards? Identify the major safety hazards and eliminate them, if possible Locate critical areas on the flow diagrams and layout drawings Is selection of a specific process route, or other design option, more appropriate on safety grounds? Can the process sequence be changed to improve the safety of the process? Could less hazardous materials be used? Are emissions of material necessary? Are necessary emissions discharged safely and in accordance with good practice and legislation? Can any unit or item be eliminated and does this improve safety, e.g. by reducing inventory or improving reliability? Is the process design correct? Are normal conditions described adequately? Are all relevant parameters controlled? Are the operations and heat transfer facilities properly designed, instrumented and controlled? Has scale-up of the process been carried out correctly? Does the process fail safe in respect of heat, pressure, fire and explosion? Has second chance design been used? Spacing distances may be reduced in the light of: • explosion relief, blast-proofing, blast walls, earth banks; • bunds, dykes; • steam and water curtains; foam blanketing provisions; • inter-positioning of sacrificial plant, e.g. cooling towers, unpopulated buildings; • provision of refuges, e.g. for toxic release incidents. Adequate distance frequently serves to mitigate the consequences of an accidental release of chemicals, e.g. a flammable liquid spillage or toxic gas escape. Distances are recommended for zoning of electrical equipment, separation of storage from buildings etc. Distances are also proposed (on the basis of experience) to minimize the escalation [...]... 17.8 20 .3 20 .3 15 .2 12. 7 17.8 20 .3 17.8 17.8 20 .3 17.8 3500–4000 4000 3000 25 00 3500–4000 3500 3500 4000 3500 15 .2 17.8 17.8 22 .9 20 .3 3000–3500 3500–4500 4000 12. 7 17.8 17.8 17.8 17.8 17.8 17.8 20 .3 15 .2 12. 7 15 .2 15 .2 12. 7 17.8 17.8 20 .3 17.8 20 .3 15 .2 20.3 25 .4 12. 7–15 .2 17.8 22 .9 17.8 25 00 3500 3500 3500 3500 3500 3500 4000 3000 25 00 3000 3000 25 00 3500 3500–4000 3500–4000 3000 4000–5000 25 00–3000... fume (ft/min) 12. 7 20 .3 25 00 4000 17.8 17.8 17.8 22 .9 15 .2 17.8 12. 7 10 .2 15 .2 17.8 17.8 3500 3500 3500–4500 3000 3500 25 00 20 00 3000 3500 3500 12. 7 17.8 20 .3 15 .2 15 .2 10 .2 2500 3500 4000 3000 3000 20 00 Fire protection The installation of fixed fire protection depends on analysis of potential fire characteristics (see Chapter 6) A summary of the factors is given in Table 12. 14 Table 12. 14 Fire characteristics... 3500 4000 3000 25 00 3000 3000 25 00 3500 3500–4000 3500–4000 3000 4000–5000 25 00–3000 3500–4500 3500 12. 7–15 .2 15 .2 16.3 15 .2 20.3 25 .4 17.8 17.8 10 .2 20.3 20 .3 25 .4 15 .2 17.8 15 .2 19.0 10 .2 2500–3000 3000 320 0 3000 4000 5000 3500 3500 20 00 4000 4000–5000 3000 3500 3000 3800 20 00 410 SAFETY BY DESIGN Table 12. 13 Cont’d Material, operation or industry Minimum transport velocity (m/s) Rubber dust fine coarse... All Synthetic organic chemical manufacturing 0 .27 0 .11 0.00 022 0 .11 0. 021 0.64 0.16 0.00 025 0.0 023 0.015 0.0056 0.0071 0.00 023 0.0494 0. 021 4 0 .22 8 0.104 0.00083 0.0017 0.015 *Multiplying the total number of items in a unit by the factor provides an indication of the emission rate Piping arrangements Complex piping systems may be required for the transfer of chemicals, balancing of pressures, venting,... Table 12. 7 Storage Chemicals in packages The design of any building or outside compound for the storage of chemicals in packages (e.g drums, cylinders, sacks) will depend upon their hazardous characteristics (pages 22 8, 24 8 and 27 2) For a storage building the considerations include: • Siting to minimize risk to nearby premises on and off site in a fire • Access for delivery and transfer of chemicals. .. Time Figure 13 .2 ‘Permit-to-work’ certificate for entry into a confined space A certificate number is added for identification, authenticity checking etc MAINTENANCE 421 Empty liquid isolate entry points Purge tank Steam Water Air Vapour present Inert tank Water CO2 N2 N2 foam Vapour test Vapour absent Inspect internally Waterfilled Residues absent CO2/N2/ foam filled Oxygen test O2 ≥5% Residues present... may impinge (b) Within 2 m in all other directions from point of discharge (a) Vertically from ground level up to 2 m above, and horizontally outwards for 2 m from any point where connections are regularly made or disconnected for product transfer (b) Vertically and horizontally between 2 m and 4 m from the points of connection or disconnection Within 2 m in all directions Zone 2 Discharge from vent... one hood 408 SAFETY BY DESIGN Table 12. 12 Range of capture velocities 0 .25 –0.51 Released at low velocity into moderately still air Spray booths Intermittent container filling Low-speed conveyor transfers Welding Plating Pickling 0.51–1. 02 Active generation into zone of rapid air motion Spray painting in shallow booths Barrel filling Conveyor loading Crushers 1. 02 2. 54 Released at high initial velocity... Figure 12. 1) If enclosure or use of a booth is impracticable, a captor hood is used This is placed some distance from the source of pollution and the rate of air flow needs to be such as to capture contaminants at the furthermost point of origin Typical capture velocities are given in Table 12. 12 Since velocity falls off rapidly with distance from the face of the hood, as shown in Figure 12. 2, any source... Fire-proof construction 4 02 SAFETY BY DESIGN Table 12. 7 Selected sources of spacing distances with hazardous chemicals (see Bibliography) Preliminary minimum distances Liquid oxygen Liquefied flammable gases Liquids stored at ambient temperature and pressure A Code of Practice for the Bulk Storage of Liquid Oxygen at Production Sites (HSE, 1977) Process Plant Layout page 5 62 (Mecklenburgh, 1985) Process . 37 Lead 82 206 Pb 82 82 124 20 6 20 7 .21 82 207 Pb 82 82 125 20 7 82 208 Pb 82 82 126 20 8 Uranium 92 234 U 92 92 1 42 234 23 8.07 92 235 U 92 92 143 23 5 92 238 U 92 92 146 23 8 Natural. 0.66 4. 82 1.63 0.65 60 Co 5 .24 years 1.17–1.33 6.68 2. 08 1 .20 198 Au 2. 7 days 0.41 4.06 – 0.33 1 92 Ir 74 days 0.13–1.06 4. 32 1 .27 0.60 22 6 Ra 1 622 years 0.047 2. 4 6.86 2. 24 1.66 Table 11. 6 General. number Very high toxicity Sr-90 + Y-90, *Pb -21 0 + Bi -21 0 (Ra D + E), Po -21 0, At -21 1, Ra -22 6 + 55 per cent *daughter products, Ac -22 7, *U -23 3, Pu -23 9, *Am -24 1, Cm -24 2. High toxicity Ca-45, *Fe-59, Sr-89,