Conociendo la RSC: Conceptos, características y áreas de actuación

We have mentioned HAZCOM, but why is this so important? One of the most serious and problematic hazards that wastewater workers have to deal with is working with hazardous chemicals. There are many that are used regularly in the wastewater treat-ment industry, including chlorine gas, hydrogen peroxide, sulfuric acid, hydrochloric acid, acetic acid, and caustic soda. There are many others with varying degrees of im-mediate hazard. Without discussing all of the hazards, the following sections discuss ways of controlling hazards for workers who use these chemicals daily.

CONTROL MEASURES. When dealing with chemicals, the economic feasibility of eliminating the use of that chemical must be a primary consideration. Too often, the use of hazardous chemicals continues because “it was always done that way”. Other methods of controls are engineering controls that lower the liability in using chemicals or ensuring safe work practices.

Elimination. The use of specific chemicals may be eliminated by changing the process (i.e., the use of anoxic zones to release some of the alkalinity during denitrification to lower the amount of chemical needed); changing equipment; or substituting chemicals that may be less hazardous to use. There are many resources that offer help, and often these are free. Chemical suppliers can suggest alternatives that may be safer to use that may not be familiar to managers. Often, state inspectors may be a helpful resource; they may suggest alternative controls that would lower liability. For example, the City of Anchorage, Alaska, reviewed its chlorine use and found that, because of chemical de-livery schedules, it had a high risk factor. Chlorine was delivered infrequently because of the city’s location, and large amounts of chlorine were stored on-site. Rather than maintain such a huge possible environmental liability, the city decided to switch to an alternative method of disinfection that uses salt for on-site chlorine generation. While the new method was more expensive, the amount of training and continuous monitor-ing that was reduced offset any economic advantages of delivermonitor-ing cheaper chlorine gas.

Engineering Controls. Primary measures include ventilation (both general and local exhaust), isolation, enclosure, and workplace redesign. Ventilation controls primarily airborne hazards to separate the hazard from the worker. Again, it is important for managers to work with local stakeholders. The local fire department or hazardous ma-terials division may be able to suggest inexpensive solutions to safety issues. If you work easily with them, they are willing to share their experience with you.

Work Practices. The following are common work practices used to help safeguard employees:

• Initial training for proper safe handling and work practices.

• Using proper PPE.

• Proper housekeeping and storage procedures.

• Developing and using standard operational procedures for routine jobs that have some hazard associated with them.

• Using vacuums or sweeping compounds to keep chemical storage areas clean.

• Prohibiting smoking in areas of possible exposure.

• Using separate eating and washing facilities where ingestion hazard is identified.

• Labeling containers properly, including appropriate National Fire Protection Agency (NFPA) (Quincy, Massachusetts) signs or other detailed information. This is particularly important when the original chemical is transported in another tainer for use. It is possible to obtain NFPA signs and stickers to put on the con-tainer. At the very least, the container should be labeled with the correct contents.

• Posting warning signs to alert employees to hazardous conditions and special precautions.

• Posting emergency instructions at critical operations.

• Having emergency procedures in place for fires, chemical emergencies, spills, and first-aid requirements and practicing them.

• Training and maintaining training records for safe use and handling of all haz-ardous chemicals.

• Using job safety analyses to help perform operation and maintenance tasks.

The training of personnel to safely handle these chemicals and the provisions of PPE cannot be stressed enough once it is determined that it is not possible to lower ex-posure to these chemicals by elimination or engineering controls.

COMMON CHEMICALS. Table 5.1 is a list of common chemicals found in waste-water treatment, their characteristics, and the most common immediate dangers they can pose to a wastewater employee.

As indicated in the table, many of the gases are colorless, odorless, and tasteless, necessitating the use of gas sensors. Gas sensor use is covered in the section on con-fined spaces.

STORAGE GUIDELINES. Standard for Fire Protection Practice for Waste-water Treatment Plants and Collection Facilities. Standard for Fire Protection Prac-tice for Wastewater Treatment Plants and Collection Facilities (NFPA, 1995) lists informa-tion regarding the storage and handling of chemicals found in wastewater treatment facilities. Sections of the Uniform Fire Code (NFPA, 2006; managers should use the cur-rent code that has been adopted and has regulatory jurisdiction in their areas) also dis-cuss the storage, dispensing, and use of most hazardous chemicals used in a waste-water treatment plant. Once the manager becomes familiar with these standards, it is important to contact the local fire and building inspectors and other appropriate offi-cials to determine who has jurisdiction and who has the most stringent standard to meet. Sometimes, officials may not agree; however, by initiating dialogue, the manager may facilitate a process whereby all inspectors and regulatory agencies can agree on practices for a particular facility.

Chlorine Storage and Chlorine Room Design. Chlorine rooms are worthy of special mention because chlorine is probably the single most dangerous chemical commonly used in wastewater treatment plants, and the storage rooms for chlorine have specific design standards. Many of these design standards can be found in design or standard practice manuals. It is a good idea to be familiar with the following basic principles, but always remember to check local building and fire codes, as they may be different and more stringent:

• Chlorine rooms should be adequately heated (typically higher than 10 ºC [50 °F]

to keep the chlorine from forming chlorine ice crystals).

TABLE5.1 List of common chemicals found in wastewater treatment, their characteristics, and the most common immediate dangers they can pose to a wastewater employee.*

Common name Physical characteristics Danger Safety precaution Chlorine gas Greenish-yellow gas, Respiratory irritant: SCBA

amber liquid under 30 mg/L coughing;

pressure, highly irritating 40 to 60 mg/L odor, corrosive in moist dangerous in 30 min-atmosphere utes; 1000 mg/L lethal

in a few breaths

Caustic soda Viscous liquid, high pH Chemical burn Gloves, face shield or goggles, chemical wash station

Sulfuric acid Liquid, low pH, Chemical burn Gloves, face shield or

distinctive odor goggles, chemical

wash station

Hydrochloric Liquid, low pH, Chemical burn Gloves, face shield or goggles,

acid distinctive odor chemical wash station

Carbon dioxide Odorless gas Asphyxiation Ventilation, SCBA

Carbon Colorless, odorless, taste- Asphyxiation, flam- Ventilation, SCBA

monoxide less gas mable, explosive

Methane Colorless, tasteless, Flammable, explosive Ventilation odorless, nonpoisonous

Hydrogen Rotten egg smell, deadens Death in few minutes Ventilation, SCBA

sulfide sense of smell at 0.2%

Hydrogen Colorless, odorless, Asphyxiation, Ventilation tasteless gas flammable, explosive

*Note that this list is not comprehensive of the chemicals found in wastewater plants or all of the dangers that they may pose but is only an example of the immediate dangers. For all of the dangers presented by chemicals on-site, please consult the MSDS sheets and the current issue of the NIOSH Guide to Chemical Hazard (NIOSH, 2005).

• There should be adequate light so that the operator can easily see what he or she is doing.

• There should be an adequate controlling and measuring method so that the chlorine can be dispensed safely. Taking too much chlorine from the cylinder in one day can also form ice crystals. Maximum flow from a 45- or 68-kg (100- or 150-lb) cylinder is 18 kg/d (40 lb/d) and from a 900-kg (1-ton) cylinder is 180 kg (400 lb).

• The chlorine cylinders should be safely fastened in place. This is typically done by using chains or clamps. It should be easy to handle and store cylinders;

45- and 68-kg (100- and 150-lb) cylinders are always stored in a vertical position.

• There should be appropriate carts, clamps, chain falls, or hoists available so that the cylinders can be moved without undue stress on the worker’s body.

• Chlorine room doors should have safety glass placed in them so that an outside observer can watch any work being performed or simple periodic visual checks can be made. When chlorine room doors are opened, they should trigger a ven-tilation fan so that the room is ventilated with fresh air whenever anyone is in the room.

• Because chlorine gas is heavier than air, the ventilation inlet is near the floor to dilute any chlorine gas that may have leaked. The outlet of the ventilation sys-tem should be away from the inlet at the top of the room and also away from any traffic patterns that may occur outside the room. This would reduce the threat of accidentally gassing pedestrian traffic. Chlorine rooms in larger plants should have chlorine detection alarms that will typically have battery backup in case of power failure.

• Outside the chlorine room, there should be a self-contained breathing apparatus (SCBA) to be worn in case of emergency entrance to the chlorine room while there is a leak. These need to be tested regularly and fit-tested on the employees that wear them.

During an emergency is not the time to find out that routine maintenance and worker practice have been forgotten. This could easily create a life-threatening situation.

CHEMICAL DELIVERY AND DISTRIBUTION.While many wastewater treat-ment professionals work in larger plants, where chemicals are delivered, there is a small percentage of operators who work in small systems, where chemicals must be brought in or moved from place to place by workers, because delivery is not immedi-ately possible. For example, there are small mountain communities where chlorine gas delivery trucks could not even make it up the road to get there. This means chemicals

must be moved in the plant’s service truck. All chemical delivery of this type falls un-der the jurisdiction of the Department of Transportation (DOT) (Washington, D.C.).

When hauling chlorine gas or sulfur dioxide cylinders, the plant’s service truck must have the appropriate DOT placards (Figure 5.2). Placarding examples can be found in DOT manuals and purchased from many safety and industrial suppliers.

There will be a need for a chain-of-custody form that shows the quantity, chemical name, emergency response telephone number, class of chemical, UN number, and quantity and class of container. It also requires the signature of the driver for the load.

This paperwork needs to be kept on a clipboard on the dash, in the front seat, or in the door panel for immediate accessibility. The MSDS sheet for the chemical also should be attached to the clipboard. Drivers need to have hazardous chemical transportation safety classes.

When transporting liquid chemicals, such as 10% sodium hypochlorite or caustic soda, there cannot be more than 450 kg (1000 lb) on the truck. That basically means one barrel, or possibly two, if the weight is known. The same protocol as above must be fol-lowed, with the exception of placarding. In either case, NFPA signage must be on the containers. When carrying containers containing less than 18 L (5 gal), no chain-of-custody paperwork or extensive protocols need to be followed. By using common sense and good common safety procedures, no chemicals that will react with each other should be carried together. All small containers that are carried still need the appropri-ate marking, class of container, and NFPA decals on the container.

NATIONAL FIRE PROTECTION ASSOCIATION. Below is a brief descrip-tion of the symbols system used by NFPA for marking chemicals (Figure 5.3; NFPA, 2005). These diamond symbols should be on all chemical storage drums and smaller containers and can be purchased from many safety suppliers. For fire protection, these symbols should be displayed outside of buildings that house chemicals.

Other symbols, abbreviations, and words that some organizations use in the Spe-cial Hazards section of Figure 5.3 are shown in Figure 5.4 (NFPA, 2005). These uses are notcompliant with NFPA 704; they are presented to help clarify their meaning when they appear on an MSDS or container label.