nebosh national diploma - rrc trainingcourse: nebosh national diploma, unit c lesson no: week 1, day...

NEBOSH National Diploma UNIT C

Workplace and Work Equipment Safety

Sample Trainer Pack

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• A ‘helicopter’ plan (MS Word) – an overview of how the course will be delivered over its duration. • Daily lesson plans (MS Word) – a suggested breakdown of how the detailed subjects specified in the qualification

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Emergency Evacuation Procedures

Directed Q & A and discussion - the purpose of and requirements for emergency evacuation procedures. Individual/Small Group exercise 5

Individual/Small Group exercise 5 In small groups ask students to use the check list they developed to conduct an actual assessment of the building

1230 - 1330 Lunch

1330 – 1700

Approx 1445

15 minutes

coffee break

C4 Storage, handling and processing of dangerous substances Industrial Chemical Processes Explanation of the exothermic runaway reaction with reference to temperature, pressure, catalysts; heat of reaction; temperature and pressure control

Suitable Video: on runaway reactions

Individual/Small Group exercise 6 Storage, Handling and Transport of Dangerous Substances Directed Q & A and discussion - storage of dangerous substances – identification and risk assessment; storage methods; segregation requirements; leakage and spillage containment Explanation of the problems associated with the handling of dangerous substances – pipelines; filling and emptying; dispensing, spraying and

Suitable Video: e.g. ‘Exothermic chemical reactions’ (show parts 1 – 3 only) by HSE. Suggested Individual/Small Group Exercise 6: A case study on a runaway reaction. E.g. could use the case study from Diploma Part 2, June 2000 (based on Bhopal)

RRC SAMPLE MATERIAL

disposal; electricity dangers Directed Q & A and discussion - transport of dangerous substances – loading and unloading of tanks; marking of vehicles and packages; DGSA Individual/Small Group exercise 7 End of session Q&A

Directed Private Study: Set revision questions from “Revision Questions” pack relevant to topics covered today

Individual/Small Group exercise 7: in groups of 2 or 3 to tackle selected exam questions relevant to topics being discussed. Whole group feedback using flipchart/whiteboard as focus

RRC SAMPLE MATERIAL

LESSON PLAN COURSE: NEBOSH National Diploma, Unit C LESSON No4: Week 1, Day 4 TITLE: C4 – Storage, handling and processing of dangerous substances (part 2)/ C5 – Work equipment (general) (part 1)

Timings Subjects to be covered Activities and Aids

0900– 0930 Group Feedback: review answers to questions from previous evening DPS (get students to take turns in scribing some answers on flip chart)

0930 – 1230

Approx 1045

15 minutes

coffee break

C4 Storage, handling and processing of dangerous substances Hazardous Environments Directed Q & A and discussion on hazardous environments - mechanical damage; solid bodies, objects and dusts; liquids and gases; wet environments including corrosion and degradation of installation; flammable atmospheres. Explanation of the principles of the design and use of electrical systems and equipment in adverse or hazardous environments. Explanation of zoning, pressurisation and purging, Intrinsically safe equipment, flameproof equipment, type ‘N’ equipment, type ‘e’ equipment. Emergency planning Directed Q & A and discussion on the need for emergency preparedness within an organisation for personal injury, explosive device, fire, loss of containment

Individual/Small Group exercise 8: In groups of 2 or 3 to tackle selected exam questions relevant to topics being discussed. Whole group feedback using flipchart/whiteboard as focus. Library resources: HSE Investigation reports of various accidents L138 – DSEAR on Storage HSG71 – storage of packaged dangerous substances RRC SAMPLE MATERIAL

© RRC International

NEBOSH National Diploma Element C4: The Storage, Handling and

Processing of Dangerous Substances

Contains public sector information licensed under the Open Government Licence v.1.0 RRC SAMPLE MATERIAL

© RRC International © RRC International

Element C4

1. Industrial Chemical Processes 2. Storage, Handling and Transport of Dangerous

Substances 3. Hazardous Environments 4. Emergency Planning

RRC SAMPLE MATERIAL

© RRC International © RRC International Temperature

Reaction Rate

Why does food last longer in the fridge/freezer ?

Chemical Reactions - Understanding the Effects of Temperature, Pressure and

Catalysts Temperature

• Rule of thumb: each 10°C rise doubles the reaction rate.

• Poor temperature control has lead to many thermal runaway reactions.

RRC SAMPLE MATERIAL


Pressure • Clearly pressurised containers may explode with some

force if containment strength is exceeded

• But increasing pressure can make gas/vapour reactions occur faster/more readily

• Sudden compression of gases increases pressure and also produces heat:

- See how hot a bicycle pump gets!

- Principles of diesel engines (no spark plug needed)

RRC SAMPLE MATERIAL


Acetylene – a Particular Problem

• Unstable compound – particularly sensitive to pressure

• Pressures above ca. 0.6 bar – can decompose explosively: – Very rapid burning – high rates of pressure rise

– Can result in explosion pressure > 10 times initial pressure

– (50 times with detonations)

RRC SAMPLE MATERIAL


Catalyst

Any agent (physical, chemical etc.) which, when added in very small quantities, notably affects the rate of a chemical reaction without itself being consumed or undergoing a chemical change.

• Most accelerate reactions

• A few retard them (negative catalysts or inhibitors)

Widely used in chemistry e.g.

• Oil refineries - catalytic “cracking” using zeolites

• Car catalytic converters – using Palladium, Platinum, Rhodium

Also in living organisms e.g.

• Enzymes – biological catalysts in digestion of food etc.

RRC SAMPLE MATERIAL


Some chemicals very sensitive to contaminants – can catalyse decomposition.

E.g. Hydrogen peroxide solutions:

• Decomposition normally quite slow

• Greatly accelerated by trace quantities of metals, rust and other contaminants:

– Produces heat (which further accelerates reaction) and oxygen gas – explosive pressure rupture of container

RRC SAMPLE MATERIAL


Chemical “reactions”

In general terms, heat may be:

• Required/Absorbed from surroundings (Endothermic) e.g.

- melting of ice (a physical change), photosynthesis (involving chemical change or “reaction”)

OR

• Released to surroundings (Exothermic) e.g.

- combustion reactions like burning wood, paper, natural gas etc. – most common reactions are like this

Heat (Enthalpy) of Reaction

Reactant(s) Product(s)

ΔH

RRC SAMPLE MATERIAL


Exothermic Reactions and Thermal Runaways

Large-scale exothermic reactions – if heat generation exceeds cooling capacity of surroundings ->

• Increased temperature, leading to

• increased reaction rate, leading to

• increased temperature…

• …rapidly accelerating thermal runaway

• BECAUSE:

- Heating depends on amount of material in the reaction

- Cooling depends on surface area exposed to environment

- So, scale-ups are more likely to lead to uncontrolled temperature rise

RRC SAMPLE MATERIAL


Some Causes of Runaway in Reactors or Storage Tanks

RRC SAMPLE MATERIAL

© RRC International Unit C – Element C4: Storage, Handling and Processing of Dangerous Substances | 4-14-PB | Unit C – Element C4: Storage, Handling and Processing of Dangerous Substances © RRC International

LEARNING OUTCOMES

On completion of this element, you should be able to demonstrate understanding of the content through the application of knowledge to familiar and unfamiliar situations and the critical analysis and evaluation of information presented in both quantitative and qualitative forms. In particular you should be able to:

Outline the main physical and chemical characteristics of industrial chemical processes.

Outline the main principles of the safe storage, handling and transport of dangerous substances.

Outline the main principles of the design and use of electrical systems and equipment in adverse or hazardous environments.

Explain the need for emergency planning, the typical organisational arrangements needed for emergencies and relevant regulatory requirements.

THE STORAGE, HANDLING AND PROCESSING OF DANGEROUS SUBSTANCES

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© RRC International Unit C – Element C4: Storage, Handling and Processing of Dangerous Substances | 4-34-2 | Unit C – Element C4: Storage, Handling and Processing of Dangerous Substances © RRC International

Contents


INDUSTRIAL CHEMICAL PROCESSES 4-3

Effects of Temperature, Pressure and Catalysts 4-3Heat of Reaction 4-4Examples of Endothermic and Exothermic Reactions 4-7Methods of Control of Temperature and Pressure 4-8Revision Questions 4-9

STORAGE, HANDLING AND TRANSPORT OF DANGEROUS SUBSTANCES 4-10

Dangerous Substances and Hazardous Substances 4-10Hazards Presented and Assessment of Risk 4-13Storage Methods and Quantities 4-14Storage of Incompatible Materials, Segregation Requirements and Access 4-18Leakage and Spillage Containment 4-20Handling of Dangerous Substances 4-22Transport of Dangerous Substances 4-27Labelling of Vehicles and Packaging of Substances 4-28Driver Training and The Role of Dangerous Goods Safety Adviser 4-29Revision Questions 4-31

HAZARDOUS ENVIRONMENTS 4-32

Principles of Protection 4-33Wet Environments 4-33Selection of Electrical Equipment for Use in Flammable Atmospheres 4-33Classification of Hazardous Areas and Zoning 4-33Use of Permits-To-Work 4-34Principles of Pressurisation and Purging 4-34Types of Equipment 4-34Revision Questions 4-35

EMERGENCY PLANNING 4-36

Need for Emergency Preparedness Within an Organisation 4-36Consequence Minimisation via Emergency Procedures 4-38Development of Emergency Plans 4-38Preparation of Major Accident Hazard Emergency Plans to Meet Regulatory Requirements 4-39Preparation of On-Site and Off-Site Emergency Plans Including Monitoring and Maintenance 4-41Revision Questions 4-43

SUMMARY 4-44

EXAM SKILLS 4-46

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Industrial Chemical Processes

© RRC International Unit C – Element C4: Storage, Handling and Processing of Dangerous Substances | 4-34-2 | Unit C – Element C4: Storage, Handling and Processing of Dangerous Substances © RRC International © RRC International Unit C – Element C4: Storage, Handling and Processing of Dangerous Substances | 4-34-2 | Unit C – Element C4: Storage, Handling and Processing of Dangerous Substances © RRC International

All chemical reactions involve changes in energy, usually evident as heat. Reactive chemical hazards invariably involve the release of energy in a quantity or at a rate too great to be dissipated by the immediate environment of the reacting system, so that destructive effects appear. It is essential for a process designer to understand the nature of the reactive chemicals involved in a process.

Careful control of chemical reactions

KEY INFORMATION

• The rate of a reaction will usually increase with temperature and pressure. A catalyst will affect the rate of a chemical reaction without being changed itself.

• Endothermic reactions take place with absorption of heat and require high temperatures for their initiation and maintenance, e.g. photosynthesis, or reaction of ethanoic acid with sodium carbonate .

• Exothermic reactions are accompanied by the evolution of heat, e.g. combustion, or the reaction of sodium and chlorine.

• A runaway reaction is an exothermic reaction where the heat generated continues to increase the temperature, accelerating the reaction out of control.

• The temperature of a chemical process can be controlled by cooling and stirring to ensure even distribution of materials and no formation of “hot spots”. Over-pressure can be prevented by safety relief valves and/or rupture discs.

EFFECTS OF TEMPERATURE, PRESSURE AND CATALYSTSThe rate of a reaction will increase exponentially with increase in temperature; in practical terms an increase of 10°C roughly doubles the reaction rate in many cases. This has often been the main contributory factor in cases where inadequate temperature control had caused exothermic reactions to run out of control.

Things can be made worse in closed systems at relatively high pressures and/or temperatures. In high-pressure autoclaves, for example, the thick vessel walls and generally heavy construction necessary to withstand the internal pressures implies high thermal capacity of the equipment. Rapid cooling of such vessels to attempt to check an accelerating reaction is impracticable, so bursting discs or other devices must be fitted as pressure reliefs to high-pressure equipment.

Substances which are highly reactive or unstable when subject to heat, pressure, mechanical force or on contact with other chemicals represent a potential source of explosive energy. Acetylene, for example, has a tendency to decompose exothermically and result in explosions or detonations. The character and course of the explosion depend upon many factors. Pressures in excess of 10 times the initial pressure can result from acetylene explosions and pressures above 50 times the initial pressure have arisen with detonations.

GLOSSARY

CATALYST

A catalyst is any agent (usually a substance) which, when added in very small quantities, notably affects the rate of a chemical reaction without itself being consumed or undergoing a chemical change. Most catalysts accelerate reactions but a few retard them (negative catalysts or inhibitors).RR

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Light can act as a catalyst (although not a ‘substance’ as such) in both the visible and ultra-short wavelengths, e.g. in photosynthesis and other photochemical reactions.

The activity of a solid catalyst is often centred on a small fraction of its surface, so the number of active points can be increased by adding promoters which increase the surface area in some way, e.g. by increasing porosity. Catalytic activity is decreased by substances that act as poisons which clog and weaken the catalyst surface, e.g. lead in the catalytic converters used to control exhaust emissions.

Catalysts can be highly specific in their application, and are essential in virtually all industrial chemical reactions, especially in petroleum refining and synthetic organic chemical manufacturing.

There are many organic catalysts that are vital in the metabolic processes of living organisms. These are called enzymes and are essential, e.g. in digestion.

HEAT OF REACTION

EndothermicEndothermic reactions take place with absorption of heat and require high temperatures for their initiation and maintenance. An example is the production of carbon monoxide and hydrogen by passing steam over hot coke.

In the relatively few endothermic reactions, heat is absorbed into the reaction product(s), which are thus endothermic (and energy-rich) compounds. These are thermodynamically unstable, because no energy would be required to decompose them into their elements, and heat would, in fact, be released. Most endothermic compounds possess a tendency towards instability and possibly explosive decomposition under various circumstances.

Many, but not all, endothermic compounds have been involved in violent decompositions, reactions or explosions. In general, compounds with significantly positive values for their standard heat of formation can be considered suspect on stability grounds. Values of thermodynamic constants for elements and compounds are available, conveniently tabulated, but also note that endothermicity may change to exothermicity with increase in temperature.

Examples of endothermic compounds are found in the following groups:

• Acetylenic compounds.

• Alkyl metals.

• Azides.

• Boranes (boron hydrides).

• Cyano compounds.

• Dienes.

• Halogen oxides.

• Metal acetylides.

• Metal fulminates.

• Oxides of nitrogen.

ExothermicAn exothermic reaction is a reaction accompanied by the evolution of heat, such as a combustion reaction.

Exothermic reactions must be carefully controlled and monitored to ensure there is no failure of the cooling or stirring systems. Quantities should be kept to a minimum and suitable screening should be provided. No operation of this kind should be entrusted to anyone apart from a highly skilled and competent chemist knowledgeable in the dangers involved and the precautions to be taken.

Most reactions are exothermic. They tend to accelerate as the reaction proceeds unless the rate of cooling is sufficient to prevent a rise in temperature. The exponential temperature effect accelerating the reaction will exceed the (usually) linear effect of falling reactant concentration in decelerating the reaction. Where the exotherm is large and cooling capacity is inadequate, the resulting accelerating reaction may proceed to the point of loss of control, and decomposition, fire or explosion may result. Reactions at high pressure may be exceptionally hazardous owing to the enhanced kinetic energy content of the system.

The rate of an exothermic chemical reaction determines the rate of energy release; so factors which affect reaction kinetics are important so far as possible hazards are concerned.

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Runaway ReactionsReactive hazards can involve the release of energy in quantities or at rates too high to be absorbed by the immediate environment of the reacting system. In these cases material damage occurs. The source of the energy may be an exothermic, multi-component reaction, or the exothermic decomposition of a single unstable (often endothermic) compound. The presence of an unsuspected contaminant or catalytic impurity may affect the velocity or change the course of reaction.

Important factors in preventing such thermal runaway reactions are mainly related to the control of reaction velocity and temperature within suitable limits. These will include considerations such as:

• Adequate heating and particularly cooling capacity in both liquid and vapour phases of a reaction system.

• Proportions of reactants and rates of addition (allowing for an induction period).

• Use of solvents as diluents and to reduce viscosity of the reaction medium.

• Adequate agitation and mixing in the reaction vessel.

• Control of reaction or distillation pressure.

• Use of an inert atmosphere.

Reactions may be:

• In gas, liquid (neat or in solution, suspension or emulsion) or solid phase.

• Catalytic or non-catalytic.

• Exothermic, endothermic or negligible heat loss/gain.

• Reversible or irreversible.

There are two main methods of operation used in reactors:

• Batch - where each chemical reaction is carried out separately with fixed quantities of materials and when the reaction is completed the process stops.

• Continuous - where the reactants flow into a vessel and products flow out so that the reaction can operate for long periods of time until the flow of reactants is stopped.

Continuous operation tends to predominate in large-scale production. It has the advantage of low materials inventory and less variation of operating variables.

Recycling of reactants, products or diluent is common in continuous reactors. This may be in conjunction with heat removal (in an external exchanger) which is an important means of controlling the progress of the reaction. To minimise hazards associated with chemical reactors it’s important to have comprehensive data on the following aspects:

• Physical.

• Chemical.

• Thermal.

• The effect of corrosion products and impurities.

• Thermal stability.

A dangerous runaway reaction is most likely to occur if all the reactants are initially mixed together with any catalyst in a batch reactor, where heat is supplied to start the reaction.

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Some causes of runaway in reactors or storage tanks

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Many chemical processes require equipment designed to rigid specifications, with sophisticated automatic control and safety devices. With some reactions, it is important to provide protection against failure of cooling media, agitation, control, or safety instrumentation, etc. The reactor itself must be adequately designed for the operating conditions, e.g. pressure, temperature, corrosive environment.

TOPIC FOCUS

The conditions that might give rise to a ‘runaway reaction’ include:

• A strongly exothermic reaction process.

• Inadequate provision of cooling.

• Catalysis by contaminants.

• Lack of temperature detection and control.

• Excessive quantities of reactants in the reaction vessel.

• Failure of mixing or agitation.

EXAMPLES OF ENDOTHERMIC AND EXOTHERMIC REACTIONS

GLOSSARY

Chemical reactions are depicted as chemical equations to explain what is happening.

In a chemical equation the tiny entities (molecules) that react with each other are shown as chemical formulae, e.g. H

2O which represents

water, CO2 which represents carbon dioxide.

Sometimes more than one molecule of a substance reacts with another one in a reaction so this is shown by a number in front of the formulae, e.g. 6H

2O

which represents six molecules of water.

When carbon dioxide reacts with water in the photosynthesis reaction we find that six molecules of each react to form one molecule of glucose (C

6H

12O

6) and six molecules of oxygen.

6CO2 + 6H

2O + sunlight energy → C

6H

12O

6 + 6O

2

Endothermic reactions require heat or energy to make them proceed:

• Photosynthesis - the process by which plants convert carbon dioxide into organic compounds, especially sugars - requires energy from the sun and is therefore an endothermic reaction.

carbon dioxide + water + sunlight energy

→ glucose + oxygen

6CO2 + 6H

2O +

sunlight energy→ C

6H

12O

6 + 6O

2

• Ethanoic acid, more commonly known as acetic acid, reacts with sodium carbonate (washing soda) but requires the input of energy to do so.

ethanoic acid + sodium carbonate +

energy

→ sodium ethanoate + carbon dioxide + water.

2CH3CO

2H

(aq) +

Na2CO

3(s) + energy

→ 2CH3CO

2Na

(aq) + CO

2(g) +

H2O

(l)

An exothermic reaction is a reaction accompanied by the evolution of heat, such as a combustion reaction.

Sodium is a reactive metal and chlorine is a powerful disinfectant. Together they react so violently that flames can be seen as the exothermic reaction gives off heat. However the product of the reaction is common salt.

sodium + chlorine → salt + heat

Na(s) + 0.5Cl2(g) → NaCl(s)

Propane is an important fuel gas and reacts exothermically with oxygen. It will burn in excess oxygen with the generation of heat to form water and carbon dioxide.

propane + oxygen → carbon dioxide + water + heat

C3H

8 + 5O

2→ 3CO

2 + 4H

2O

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METHODS OF CONTROL OF TEMPERATURE AND PRESSURE As we have seen, many chemical reactions produce heat, i.e. they are exothermic. The heat raises the temperature of the reactants and causes the reaction to accelerate. The larger the amount of material, the more heat is produced. This is because heating depends on the volume of material but cooling depends on the surface area exposed to the environment. So, one way of controlling the temperature is to keep the batch size small.

In most batch processes on an industrial scale, the reactor needs to be cooled and stirred. Some safety devices could be:

• Internal cooling coils (more responsive than an external jacket).

• Sensor for rotation of stirrer blades.

• Limited feedpipe size for catalysts to limit possible over-addition.

• Duplicated thermometers or thermostats.

• Automatic shut-off valves.

• Duplicated dump valves (in case of malfunction).

• Explosion reliefs (bursting discs, blowout panels).

• Generally fail-safe equipment.

Sometimes it is possible to moderate chemical processes:

• Refluxing: boiling removes heat, so that the boiling point of a component or added solvent fixes and limits the temperatures which can be reached.

• Dilution: a large excess either of an inert additive or of one component acts as a heat sink.

Continuous processing avoids many of the problems associated with large inventories and runaway reactions. Frequently the reason for using them is related to poor mixing between phases, leading to slow processing. Tubular reactors, perhaps working under intensified conditions, limit the inventory, are highly reliable and can be isolated in sections, reducing the consequences of a malfunction. These reactors lend themselves to vapour phase reactions which often run much more smoothly.

All process designs should aim to produce an inherently safe facility - i.e. one where a worst-case event cannot cause injury or damage to people, equipment or the environment. Safety features that are built-in at design stage, rather than added on later, together with use of high-integrity equipment and piping, provide the first lines of defence against the effects of over-pressure and subsequent rupture.

A further safety layer can be provided by using depressuring or instrumented shutdown of key equipment to control any over-pressure without activating pressure relief devices. Relief devices may no longer be reliable once used, and maintenance of them is often sporadic, so this redundancy serves to minimise the probability of such devices failing.

However, over-pressure protection must still be provided, regardless of the number of lines of defence and depressuring systems in place. Emergency pressure relief systems need to be designed for high reliability even though they should only have to function infrequently, as they are the last line of defence.

The relief system protecting heat exchangers and other vessels must be of sufficient capacity to avoid over-pressure in cases of internal failure. Most equipment failures leading to potential over-pressure situations involve the breakage or rupture of internal tubes and the failure of valves and regulators.

Runaway temperature and pressure in process vessels can occur as a result of many factors, including excessive feed rates or temperatures, loss of cooling, feed or quench failure, contaminants, catalyst problems and agitation failure. The major concern is the high rate of energy release and/or formation of gaseous products, which may cause a rapid pressure rise in the equipment. In order to assess these effects properly, the reaction kinetics must be known or obtained experimentally.

The most common method of over-pressure protection is by safety relief valves and/or rupture discs which discharge into a containment vessel, a disposal system, or directly to the atmosphere.

Chemical process control

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REVISION QUESTIONS

1. In general terms, how is the rate of a chemical reaction affected by temperature?

2. What are the two key factors in controlling a thermal runaway?

(Suggested Answers are at the end.)

MORE…

Information on identifying the main hazards of carrying out chemical reactions and guidance on how to ensure a safe operation is contained in INDG254 Chemical reaction hazards and the risk of thermal runaway.

INDG254(rev1) is available at: www.hse.gov.uk/pubns/indg254.pdf

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nebosh national diploma - rrc trainingcourse: nebosh national diploma, unit c lesson no: week 1, day...

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