CHEMICAL CLEANING SAFETY - Main safety factors to carry out a Chemical Cleaning project - Engineering - http://maxpages.com/jpchemical/CHEMICAL_CLEANING

Chemical cleaning and safety

(aaa) A few words about safe cleanup in case of emergency.
SPILL RESPONSE GUIDE

(1) Waste Handling
Absorbent pads, pillows, or loose sorbent, OR
Acid neutralizer such as Spill-X-A, Neutrasorb, sodium
carbonate (soda ash), sodium bicarbonate, or calcium
carbonate

(2) PPP. Protective equipment
Splash goggles
Lab coat or apron
Shoe Covers (optional)
Chemical-resistant gloves
Sealable container
Plastic mixing tools
Heavy duty waste bags
Tape to seal bags
Hazardous waste labels

(3) Response Actions/Cleanup Methods
Alert others in the spill area.
Don’t touch or walk through the spilled material.
Shut off ignition sources.
Wear eye and skin protection. Use gloves compatible with acids such as a thick nitrile or neoprene. Avoid breathing
vapors.
As quickly as possible, dike the spilled liquid to prevent spreading.
o Spill pillows, pads, or a general absorbent material may be used.
o Use only inert non-combustible absorbents with oxidizing acids.

If acid is neutralizable**, use a weak base such as sodium carbonate (soda ash), sodium bicarbonate, or calcium carbonate.
o Add neutralizer slowly and work from edges of spill inward. Use caution because the reaction can cause splattering.
o Mix the neutralizer with a plastic spatula or other tool. Be sure to mix well to assure material is neutralized.
o Test pH or use product’s color indicator to determine level of neutralization.
o When pH is 6-8, it is no longer considered hazardous waste. The neutralized material may be carefully dissolved in water and washed down the sink.
o Any items used to absorb or dike non-neutralized acid should be considered corrosive and disposed of as hazardous waste.

o After the neutralized spill material has been picked up, spray the area lightly with water; test with pH paper to ensure all corrosive material has been removed.
Clean up spill with absorbent if it’s not recommended to neutralize the acid** or if a neutralizer is not used.
If solid, you do not need to neutralize or absorb.
Pick up spill cleanup materials with plastic tools and place into a plastic or glass container with a sealable lid. The material
may also be double-bagged and placed into a sealable cardboard box.
Label material for collection by HPO.
Thoroughly ventilate the area after cleanup.
Clean the area with detergent and water after the spill cleanup.

**Acids that may be neutralized include hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid.
Do not neutralize acids that contain heavy metals or are oxidizing acids. Examples of acids that you should not neutralize include chromic acid, perchloric acid, and fuming nitric acid. Do not neutralize hydrofluoric acid.
Note – some acids may not be washed down the drain even if neutralized because they have other characteristics that make them hazardous; for example, neutralized chromic acid cannot be sewered because it contains the toxic heavy
metal chromium. For these acids, simply absorb the material, rather than neutralize it.

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(bbb) A few words about a safe Chemical Cleaning !

The Operation

The operating company can carry out chemical cleaning but in many instances, a specialist contractor is employed. In the former case, it may be possible to build in a facility to carry out cleaning on a routine basis. In the latter case, it will require the handling and installation of temporary equipment. The actual chemical cleaning operation involves the construction of a temporary pipe work rig connected to inlets and outlets of the plant to facilitate the circulation of chemical solutions around the various parts of the system. The circulation is usually achieved with the aid of electrical or diesel pumps although there are other techniques1. The cleaning chemicals are dissolved, mixed and diluted as appropriate in a mixing tank, which is then incorporated into the circuit to allow the chemicals to be pumped into the circulating stream.

Chemical cleaning of large-scale industrial plant is an established procedure and finds application in most power stations, petrochemical works and factories with process and utility plant.

Before embarking on such a cleaning operation, the Health and Safety implications of any process and procedure must be closely looked at if accidents and incidents are to be prevented. A risk assessment must be carried out on all stages of the planned operation. Some of the key areas are discussed below.

The Choice and use of Chemicals
The first decision that has to be taken is which chemicals can be used. This will probably be governed by the nature or soiling that has to be removed e.g. the use of an acid to remove iron oxides. If there is a choice, then we must look at the protocol as well as the price. We should not be using a strong or toxic material such as hydrochloric, sulfuric or oxalic acid if a mild citric acid solution will do the job. Similarly to remove grease and oil why use a corrosive caustic soda solution if a mild detergent wash will be equally effective?

Having decided on the chemicals that are best suited for the task we must look at their nature and form. Many strong acids give rise to fuming and a consideration to using lower concentrations with no or reduced fuming must be considered. If a solid chemical is chosen, can it be purchased in the least dusty form such as prills or as a large crystalline form that is not going to create an inhalation problem for operatives who will have to tip bags of the material into a mixing tank? Because of the transient nature of this type of work and the fact that it is usually done outdoors, it is difficult to provide an engineering solution to hazardous chemical exposure. Therefore practically all control methods call for the use and wearing of personal protective clothing in the form of chemical protective suits, gloves and full face shield with chin guard .(Fig 2) In addition respiratory protection maybe needed to give protection from harmful dusts or fumes ; the power respiratory type hoods have been found to be ideal in this situation.

Prior to a clean, chemicals will be delivered to the site. These should be kept to the minimum quantities required and delivery arranged to be as near as possible to the start date of the actual chemical process. They will need to be stored in a secure, labeled and bunded area.

Neutralising chemicals,Cleaup chemicals and sorbents, eye wash bottles, a source of running water and a safety shower must be in the immediate vicinity of the chemical addition / injection area to deal with any personal contamination.
If a person becomes contaminated with a chemical they must stop work immediately, wash it off with plenty of fresh water, and then seek further assistance as indicated. The only additional action to be taken is when fluoride based chemicals are involved and these need an antidote treatment. This is available in special first aid kits, which contain calcium gluconate gels, tablets and ampoules of liquid gluconate for injection by a medical practitioner.

Similar precautions must be taken when dealing with the effluent from a cleaning process. This is normally neutralised or treated on discharge to storage tanks or lined pits where it is held prior to being removed by a licensed waste disposal organisation.

The Mechanical concern
In order to circulate the chemicals around a plant or unit, connections must be made to the permanent plant. This will entail breaking into the plant and therefore a permit to work must be obtained. This will ensure that the plant is empty and permission has been granted by the plant engineer for the breaking of flanges etc to make temporary connections. The building of a temporary rig out of pipe work, sometimes up 10" diameter and 10 ft long, poses serious manual handling problems and the use of cranes and hoists must be used wherever possible and team lifting where this is not practical. The building of the rig may involve difficult access to remote parts of the plant. Scaffolding may therefore be required and even the wearing of safety harnesses if working at a height at an exposed and unprotected edge. The rig must be so designed to give a low point for draining. Isolation valves must be incorporated in numerous places. Any leaks can then be isolated quickly and locally thereby reducing the risk of having a 100 tonnes of hot acid on the floor ! Non-asbestos based gaskets should be used in joining the pipe work and fittings. On completing the construction, the integrity of the plant and temporary circulating system must ascertained by a hydraulic test on all the systems involved in the clean prior to filling with chemicals.
Diesel pumps can be quite noisy and measurements have shown the sound levels to be in excess of 100 dB(A) at one metre. If possible electric pumps should be used as, they are quieter. Otherwise the area must be designated a hearing protection zone and appropriate hearing protection worn. Live steam injection also gives rise to levels of noise above 95 dB(A)

Safety & Environmental Management
If work is to be carried out safely then good safety management must be exercised. This will include risk assessments of the various activities e.g. unloading chemicals, pump installation, connections to client terminal points and pressure testing. There will need to be safe systems of work drawn up and the work force informed of the correct procedure to be followed through toolbox talks. Assessments 2 for PPE and Manual Handling 3 have to be in place.
By the very fact that chemicals are going to be handled and used must immediately ring warning bells concerning the protection of the environment. While safe systems for handling chemicals maybe in place to prevent contamination of personnel, there must also be arrangements and plans to protect the environment from spillage and leaks and unexpected releases. These should include drip trays for tanks and pumps, proven methods of opening containers and transferring the contents into the system without spillage e.g. use of chemically resistant hose and correct fittings. All chemical storage and handling areas must be bunded. Neutralising agents and absorbents must be to hand to deal with any leaks or spills and the system kept closed as much as possible to prevent release of fumes and vapours.

Procedures and Training
Throughout the time that chemical solutions are circulating in the system, the operation team must be vigilant and walk the rig to inspect for leaks. Checks must be carried out to ensure that vents are working and that valves are not bypassing in either direction. Any pressure gauges or flow meters must be checked at regular intervals.
Clear method statements of how the clean is to be carried out and the procedure to be followed must be drawn up by competent engineers. Valves for directing the flow in the rig must be clearly labelled and the direction of flow in the pipe work indicated with signs.

Organisation.
The chemical cleaning team will probably consist of a project engineer, supervising engineers and operators working shifts, which will go on round the clock when the chemical process is underway. Chemists and a safety advisor will probably visit the site as required. This team must be trained and knowledgeable on what they are doing and how to do the various tasks. The skills that are required include fork truck driving, rigging and slinging, hazardous chemical driving, emergency aid and pipe fitting as well as handling chemicals and the wearing and maintenance of protective clothing. Most sites employing a contractor require the people coming on to their site to hold the ECITB National Safety Awareness Passport. It is a good practice to have team talk/tool box talk at the beginning of each shift to discuss what is happening and to highlight the potential hazards of the next shifts work programme.
If an enclosed space such as a tank or boiler drum has to be entered to carry out some engineering work or inspection then the full requirements of the Confined Space Regulations 1997 must be followed. If entering an enclosed space after a clean the space must be allowed to cool to ambient temperature and have been well ventilated of all possible chemical residues. There have been incidents4 of temporary blindness associated with fumes arising after a clean from chemical breakdown products of a corrosion inhibitor.

On completion of the cleaning programme, the temporary rig must be flushed thoroughly with water so that any liquid leaking out when the pipe work is dismantled will present no hazard to the person or the environment.

Additional Safety Concerns
Consideration must also be given before the clean on what if any reaction products may be produced between the deposit being removed and the chemical cleaning solution. Carbon dioxide (CO2) will be produced in dissolving hard water scale with acid and the risk of asphyxiation inside a vessel or in a poorly ventilated area around the plant could result. Sulphide based deposits will generate toxic hydrogen sulphide gas (H2S) with acidic media. If this latter situation is likely to be realized then a totally enclosed system will have to be adopted and the gas scrubbed out with the aid of a knock out pot or vented to a flare stack where this exists on site. Where toxic gases are likely to be encountered both static and personal monitor should be utilised in the operational area.
Often a cleaning procedure will entail the heating of the chemical solution. This can be via the use of "live steam" supplied by the operating company or may have to be generated via the use or a portable boiler or water heater. The use of live steam while very handy must be introduced into the system either with the aid of steam coils in the mixing tank or through a properly designed direct contact steam injection arrangement. Open ended steam hoses into a mixing tank should not even be considered. The use of pressure reducers and correctly rated steam hose and couplings must be ensured. Any portable boiler must be supplied with its current certificate of examination and clear instructions on how to operate it. Precautions must be taken to prevent people coming into contact with the temporary pipe work rig when a hot process is being carried out. The lagging of all the temporary pipe work is not usually a practical option. Barriers and warning signs are normally used to address this problem.

Compressed gases are also occasionally used. Air is used to run a pneumatic injection pumps and to aid circulation1 while nitrogen maybe used in order to drain a system under an inert blank to prevent rusting. Correctly rated hoses, fittings and regulators must be employed if the are to be handled safely. Where a system has been drained or is being stored under an inert gas, signs must be posted around the plant to alert people that an asphyxiating atmosphere exists within the unit.
When the plant is being tested, filled, heated or chemicals are being injected into the unit, the area must be securely isolated so that third parties cannot gain access and signs displayed to highlight the hazards and that entry is prohibited. The cleaning team must police this so that should any leaks or spills occur, nobody without protective clothing will be in the vicinity to get contaminated or injured.

Fire
The main fire risks are in the operation of the diesel and electric pumps and these should be regularly serviced and have a fire extinguisher position close them. Another fire and indeed explosion hazard does potentially exist. When using acidic solutions to clean a metal, the acid besides dissolving away the scale will react with the metal surface. To prevent this, organic based corrosion inhibitors are used. However, this does not completely prevent corrosion so there is always the chance that hydrogen gas will be given off either at the open mixing tank or at any vent point. Therefore smoking must be prohibited in the immediate cleaning area.

Conclusion
Chemical cleaning of large and complex systems has many advantages over dismantling a plant and manually cleaning it e.g. time and cost. This technique has been successfully applied for many years all over the world but will only continue to be an attractive procedure if it can be carried out safely by contractors who have both knowledge and experience. Good planning, and the use of experienced and trained personnel will go a long way to reducing the risk to a low order.

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Page Updated Fri Dec 12, 2008 8:48am EST