CHAPTER 8

CHEMICAL SAFETY

7.0 CHEMICAL EXPOSURE CONTROLS

 

7.1  Chemical Fume Hoods

7.1.1  Hood Maintenance

7.1.2  Proper Hood Use

7.2  Personal Protective Equipment


7.1       Chemical Fume Hoods

Chemical fume hoods are the primary engineering control for chemical exposures in a laboratory environment.  A chemical fume hood is an enclosed ventilated cabinet to contain and exhaust contaminated air away from the worker.  Employees work with chemicals inside the chemical fume hood.  Air is drawn into the cabinet from the room through a space between the cabinet and the sash opening on the front of the cabinet.  This draws contaminated away from the worker’s breathing zone and exhausts it outside of the building. 

For a chemical fume hood to provide the designed protection, it must be maintained and used properly. 

7.1.1       Hood Maintenance

Certification of a chemical fume hood is based upon the average face velocity and the overall condition of the hood.  To be certified for use, hoods must have an average face velocity of 100 fpm with a minimum of 80 fpm at any test point.  In addition, the overall condition of the hood must be acceptable per other inspection criteria (i.e., no damage to any components, components functioning properly). 

If the above certification criteria are met, then the hood will be labeled with the operating sash height, designated with an arrow (operating sash height is the height at which optimum face velocities are achieved for capture of contaminants), and the certification date as well as the due date.  If the certification criteria cannot be met with minor adjustments, the hood will be labeled “Danger – Hood Not Working – Do Not Use”.  Facilities Operations And Maintenance (FOAM) and EHS B&C will notify the user what is needed to certify the hood, or if necessary, to replace it.

7.1.2       Proper Hood Use

The following work practices must be followed to ensure optimum protection by the hood.

·  Maintain the sash at the optimum operating height as designated by the arrow label.

· Keep the inside of the hood clean and uncluttered.  To the extent possible, do not store chemicals or equipment inside the hood as this may adversely affect air flow and containment of the hood.  Equipment that must go in the hood should be raised to allow air flow on all sides and must not block the slots in the back of the hood.

· Check baffles to ensure they are clean, open and unobstructed.

· Ensure all chemicals and equipment are used at least six inches behind the sash.

· Ensure the flow monitoring device indicates adequate flow before each use.

· Do not put your face or head inside the hood.

· Wear all required PPE, including eye protection when working in the hood.  Use of the hood does not eliminate the need for PPE.

· Make movements slowly to decrease air turbulence as this can compromise the hood’s performance (i.e., move hands in and out of the hood slowly, open and close the sash slowly).

· Try to minimize foot traffic behind the person working at the hood as this can compromise the hood’s performance. 

If the hood malfunctions in any way, discontinue use and report it immediately to EHS B&C.  EHS B&C works closely with FOAM to repair and maintain chemical fume hoods.

 

7.2       Personal Protective Equipment

When working with hazardous materials (chemical, biological or radioactive), the minimum personal protective equipment worn should be a lab coat, eye protection, closed toed shoes and appropriate chemical resistant gloves.  If working with physical hazards (e.g., temperature extremes, sharp objects or tools), then appropriate work gloves (e.g., Kevlar, leather) should be worn.  Additional PPE should be worn as deemed necessary by a hazard assessment of each task.  For assistance with hazard assessment and PPE selection, contact EHS B&C. 

            Glove Selection

            Some factors that should be considered when selecting gloves include the following. 

· Gloves may have pinholes or tears in them right out of the packaging.  Inspect gloves for pinholes and tears before use.

· Disposable chemical gloves must not be reused.  Once a glove comes in contact with a chemical, even after removal, the chemical continues to permeate the glove material.  Dispose of disposable gloves immediately after removal.  Wash hands after removing gloves.

· Although latex is the glove of choice when working with biological materials and infectious substances, the potential for latex allergies should be considered.  In general, any waterproof glove is acceptable for this work, so alternatives to latex are available.

· If a bulky glove is needed for chemical protection, but this compromises manual dexterity, a glove with better dexterity can sometimes be placed over the bulky glove improving dexterity while still providing the necessary chemical resistance.

· When wearing gloves, be cognizant of not contaminating items that may be handled by personnel not wearing gloves (e.g., door knobs, elevator buttons, telephones, computers). 

            Choosing appropriate chemical resistant gloves depends on the glove material and the chemical’s ability to degrade or permeate that material.  In addition, manual dexterity for the task should be taken into account.  Chemical glove selection charts listing most common chemicals are readily available (e.g., www.bestglove.com, or www.ansellpro.com/download/Ansell_7thEditionChemicalResistanceGuide.pdf).  Most glove manufacturers have this information available on their website.  It is best to use the website for your glove manufacturer because the same glove material used by different manufacturers may offer different levels of protection based on glove thickness and material formulation.  The time it takes for a chemical to permeate a glove material is known as the breakthrough time.  Note that if working in temperatures above room temperature, permeation rates may increase resulting in shorter breakthrough times.   Ideally a glove material that is not degraded by the chemical, and that has a long permeation time (at least longer than the task involving the chemical), should be selected.  When activities involve a combination of hazards, protection for each hazard should be taken into account.  Double gloving may be appropriate in some cases.