Storage, Handling and Processing of Dangerous Substances Flashcards
Industrial Chemistry
Raw materials > Primary bulk chemicals > Secondary commercial products
Rate of Reaction in Chemical Production
Quicker it is made the quicker it can be sold
Variables which effect the rate of reaction
Temperature Pressure Concentration Surface area of reactant Catalyst
What is a catalyst?
A substance that alters the rate of reaction without becoming permanently involved in the reaction
Exothermic reactions
Energy is given out by reactants as they form products, causing the temperature of the surroundings to rise
Endothermic reactions
Opposite of exothermic. Energy is taken in by the reactants to form products.
Energy comes from the surroundings which lose energy and cool down, resulting in a drop of temperature
Thermal Runaway reactions
Begins when the heat produced by an exothermic reaction exceeds the heat removed.
Surplus heat raises the temp. of the reaction mass and accelerates the rate of heat production
Risk from thermal runaway
Reaction vessel may become over-pressurised due to violent boiling or rapid gas generation
Harmful effects of thermal runaway
Boiling over of the reaction mass
Large increase in temp. and pressure resulting in explosion
Blast and missile damage
Secondary fires and explosions
Contamination of the wokrplace by hot liquid or toxic materials
Toxic clouds that can spread offsite
Causes of thermal runaway incidents
Inadequate understanding of the process chemistry and thermochemistry
Inadequate design for heat removal
Inadequate control and safety systems
Inadequate operational procedures, including training
HAZOP
Hazard Operability Study - structured method for identifying chemical process hazards
Methods of control to ensure safe operation of Chemical Processes
Inherently safer methods, which eliminate or reduce the hazard
Process control, which prevents a runaway reaction occurring
Protective measures, which limit the consequence of a runaway
Examples of inherently safer methods
Replacing hazardous materials with less hazardous
Having less unreacted material in the reactor, using a continuous process instead of a batch reactor
Using a semi-batch method
Using a heating medium which has a max temp. that is too low for the reaction mixture to decompose
Batch reactors
All reactants are added to a reactor at the start of the reaction. The process stops when chemical reactions are complete
Continuous processes
Reactants continually flow into and products continuously flow out of, the reactor system
Semi-batch methods
Reactants are added in a controlled manner throughout the process. Product is only removed at the end of the reaction
Process control
Includes the use of sensors, alarms, trips and other control systems that either take automatic action, or allow for manual intervention to prevent the conditions for a runaway to occur
Variables controlled in process control
Temperature
Reactant addition
Agitation
Others; PH, conductivity, concentration and pressure
Examples of protective measures
Designing plant to contain maximum pressure
Emergency relief vents
Crash cooling
Reaction inhibitors
Dumping the reaction into a quenching fluid
Legislation covering control of substances that can cause fire and explosions in the workplace
Dangerous Substances and Explosive Atmospheres Regulation 2002 (DESEAR)
Requirement under DESEAR
Employers to assess the risk of fire and explosions that may be caused by dangerous substances in the workplace
Forms of Dangerous Substances
Liquid, gas, vapours or dusts
Dangerous substances include….
Substances covered by CLP regulation
Any dust that when forms a cloud can explode
Any other substances not covered by CLP that could cause a fire or explosion in a workplace (like high flashpoint liquids)
5 steps in a DESEAR risk assessment
- Identify hazards
- Identify who may be harmed and how
- Evaluate risks
- Record significant findings
- Review and revise