Handling Of Compressed Air And Gases
Compressed Air And Gases
Compressed air and gases must be treated with seriousness. These simple principles will help to minimise any danger of any incident. Cylinders are normally of solid drawn steel and must be treated with care. They should not be subjected to shocks, falls, or undue heating. Cylinders should always be stored upright. Grease and oil must not be allowed to come in contact with the cylinders. All cylinders must be treated as if full.
Cylinder valves should be opened slowly. Improvised tools must not be used for this purpose.
Always use a two-stage regulator on the gas cylinders i.e. with two gauges on the regulator, one showing cylinder pressure and the other outlet regulated pressure. Regulators should be used for gases for which they are intended and marked. Keep regulators in good shape and maintained order.
When connecting a regulator to a cylinder it is important that regulator connecting threads are aligned accurately. If threads are misaligned and forced to thread in it is possible to damage the regulator or cylinder head or both seriously.
Leaks sometimes occur between the regulator and cylinder. If a valve seat is leaking which is rare, a temporary measure is to attach a regulator to it and seek help from the concerned safety people. If a flammable gas is involved the cylinder should be immediately moved to a safe place (open area), taking care to avoid possible sources of ignition.
Leaking cylinder must not be left on its own. If the leak is between cylinder valve and the regulator, which is most common, close the cylinder valve and attend to the connection between the regulator and the cylinder valve. Ask for assistance as appropriate. Connecting hoses should be of sound construction and of approved standard for the working pressure.
Handling Of Liquefied Gases
Handling of liquefied gases must be considered more hazardous than the handling of liquid and solid materials. It is important that the hazardous properties of liquefied gases such as flammability, toxicity chemical activity and corrosive effects be well known. Every effort should be made to learn these various properties before the gas is put to use.
Liquefied gases have unique properties like pressure, high diffusion, low flash points (for flammable gases), low boiling points and in certain cases no visual and/or odour detection. Hazard may arise as a result of equipment failure, leakage from systems and improper use of pressure controls.
Diffusion of leaking gases may cause rapid contamination of the atmosphere, giving rise to toxicity, anaesthetic effects, asphyxiation and rapid formation of explosive concentrations of flammable gases.
- The flash point of a flammable gas under pressure is always lower than the ambient, therefore, leaking gas can rapidly form an explosive mixture with air.
- Low boiling point materials can cause frostbite on contact with living tissue. This is common among the cryogenic liquids, such as liquid nitrogen, liquid oxygen and liquid air etc.
- Other effects of some liquefied gases are similar to hazards found with other chemicals e.g. corrosion, irritancy, and high reactivity.
Steps Necessary For Safe Working With Liquefied Gases
The procedures adopted for the safe handling of liquefied gases are mainly centred on containment of material to prevent its escape to the atmosphere and proper control of pressure and flow.
For the controlled removal of the liquefied gas, a manual valve is used. It must be remembered that withdrawal of liquid must necessarily be done at the vapour pressure of the material. Any reduction of pressure will result in flashing of all or part of the liquid to gas phase, therefore leaking gas can rapidly form an explosive mixture with air.
Rapid removal of a gas from liquefied gas may cause the liquid to cool too rapidly causing the pressure and flow to drop the required level. In such cases, cylinders (lecture bottles) may be placed in a water bath to prevent the drop in temperature of the cylinder.
Hazards of toxic, flammable and corrosive gases can be minimised by working in well-ventilated areas. Where possible, work should be carried out in an extracted wet bench. Leaks should no be allowed to go unchecked.
Precautions Necessary In The Use Of Liquefied Gases
Cylinders that develop leaks should be treated as follows:
- Cylinder valve packing leaks can usually be corrected by tightening the valve packing nut. Clockwise for acidic gases and anti-clockwise for base gases viewed from above. If valve leak persists inform the supplier immediately. Remove the cylinder to a hood or location where the leakage cannot cause damage until the contents can be safely dealt with.
- On rare occasions, the emergency action may be necessary in order to move a leaking cylinder to a location where it can vent safely.
Cylinder Information
In the case of speciality gases valves to open and close cylinder are occasionally not equipped with the hand wheel and require special cylinder key or wrenches to effect operation.
A valve pack nut contains packing gland, packing around the stem and it should not be tampered with. It may be tightened if a leak is observed.
A valve outlet is for connection to pressure or flow regulating equipment. Only use supplier or manufacturer’s recommended gas regulating equipment.
Water Hose Connections
Water hose connections to the taps and the equipment and the condensers in reflux or distillation set up must be secured with hose clips which can withstand fluctuation of water pressure.
Safety Data Sheets
Safety data sheets are available Dr Munir Ahmad in room 707 and can be accessed via internet from, www.sigma-aldrich.com
For COSHH Purpose Chemicals Can Be Divided Into Subgroups According To Their Characteristics
One COSHH form can cover each category except high-risk chemicals. This doesn’t mean any chemical is exempt from COSHH assessment. It only allows you to add the new chemical to already completed COSHH form for that category.
General Solvents
Methanol, Ethanol, 2-Propanol (IPA), Acetone, Butanol, Butyl acetate, Ethyl acetate, Ethylene glycol, etc.
Hydrocarbons & Chlorinated Solvents
Toluene, Xylene, Hexane, Cyclohexane, Trichloroethylene, Dichloromethane, Chloroform, Carbon tetrachloride etc.
Acids
Sulphuric acid, Nitric acid, Hydrochloric acid, Acetic acid, Phosphoric acid, Oxalic acid, etc.
Bases
Sodium hydroxide, Potassium hydroxide, Ammonium hydroxide, Tetramethylammonium hydroxide (photoresist developer) etc.
Inorganic Chemicals
Copper sulphate, Nickel chloride, Calcium phosphate, Erbium chloride, Ytterbium chloride, Aluminium chloride, Titanium isopropoxide, Zirconium propoxide, Silver nitrate, Potassium nitrate etc.
Organic Chemicals
Acetic anhydride, Urea, Pyrocatechol, Butoxyethanol, Cyclopentane, Dimethylbutane, Photoresist, N, N-Dimethylformamide, 1-Methyl-2-Pyrrolidinone, etc.
High-Risk Chemicals
Cyanides, Mercury compounds, Lead compounds, Arsenic compounds, Cadmium compounds, Ethylenediamine, Hydrofluoric acid, etc. Clean rooms are a multi-user facility and they house a variety of expensive, delicate and precision equipment and chemicals which pose significant hazards if handled incorrectly. It is not possible to define a policy for every conceivable situation. Rules and policies are no substitute for common sense. Anyone who fails to act in a safe and responsible manner may be banned from further use of the clean rooms. Clean rooms also operate under COSHH regulations.
