CHEMICAL LABORATORY SAFETY PROTECTION AGAINST THE ODDS

Objectives

Safety and health professionals use a philosophy of protection for dealing with all unacceptable risk in all occupations. These principle steps in order are:

Eliminate the hazard or reduce it

Use engineering controls

Use administrative controls

Use personal protective equipment

Eliminate the hazard or reduce it

Eliminating the hazard or reducing it to an acceptable level by: 

• substituting less hazardous materials

  A less hazardous chemical with similar properties can sometimes be substituted.

  Examples:

  • Eliminating volatile organic solvents with less volatile ones.
  • Diluting compressed gases with inert gases to lower its LEL, toxicity or reactivity.

• Changing the Process

Sometimes changes in a process can make it safer.

Examples:

• decreasing the temperature or adding reactants more slowly can make it less likely to run out of control.
• keeping unstable materials wet, reducing their sensitivity to shock.

• Reducing the Scale

Scaling down the reaction can result in smaller accidents and smaller amounts of waste.

Smaller reactions are less likely to overheat due to increased surface area.

Buy quantities suited to immediate need.

These can be achieved while still ending up with the initial desired results.

Use engineering controls

In spite of your best effort, you would find that some hazards cannot be eliminated or reduced to an acceptable level by material substitution, process changes or reducing the scale. The next step to use is engineering controls.

Engineering Controls are protective devices that isolate or contain hazards.

FUME HOODS

Ventilation is a common protection against exposure to inhalation.

Fume hoods provide a flow of air away from the person.

The speed of airflow at the front of the hood is called the face velocity.

ACGIH and others suggest an airflow of 80 - 100 linear feet per minute (lfpm).

Too high an air flow can cause turbulence. This can cause things being blown around in the hood, vapours blown back out, and excess vibration.

Face velocity can be controlled by the sash (the window) position.

The position with the minimum acceptable face velocity should be marked.

Important Operating Rules:

• Keep all operations at least 6 inches from the front edge of the hood.
  • Vapours may escape or apparatus which is to close to the edge might cause turbulence.
• Keep traffic in front of the hood to a minimum to avoid excessive air currents.
• Do not use the hood to store chemicals and/or equipment.
  • in the case of a fire or explosion, it might involve the stored chemicals.
  • storage of chemicals and equipment might also affect air flow within the hood.
• Check the air velocity at least daily.

 CLEAN BENCHES

Clean Benches are designed to protect the materials inside from contamination.

There is little or no inward air flow.

LOCAL EXHAUST

Sometimes fume hoods cannot be used due to size or other problems.

In this case, local exhaust is positioned in the area where the vapour may be vented.

A good example of this would be the vent over your kitchen stove.

GLOVE BAGS

Glove bags are plastic bags equipped with gloves. The bags are used to isolate toxic or moderately air/water reactive materials from the user and from the room atmosphere.

Do not use glove bags for flammable or highly reactive materials because the plastic bag may burn with your arms inside.

DRY BOXES

A dry box is a sealed container equipped with gloves and is designed for working with materials that must be protected from outside air or moisture.

The boxes contain a dry inert atmosphere.

To provide a dry and inert atmosphere, dry boxes have a positive pressure on the inside (higher pressure than the outside). This assures that any outside gases and moisture cannot come into the box against an outward flow of gases.

If flammable materials are to be used, an oxygen monitor should be provided.

GLOVE BOXES

Glove boxes are designed to protect the user from hazardous materials which are being worked with from within the box.

The inside of the box contains a negative pressure and there is a pass through chamber to move items into and out of the box (air lock).

When working with flammable materials inside a glove box, caution should be taken since there is very poor ventilation within the box thus causing an increase in flammable vapours.

SHIELDING

Shielding is the best engineering control against hazards from explosions or violently erupting reactions. Do not rely on the sash of a fume hood for this.

STORAGE

Good storage cabinets are another way to help isolate hazards.

Be careful to check the incompatibility of materials so that they are not stored next to each other or in some cases they should be placed in another area.

(Handbook of Reactive Chemical Hazards - Bretherick)

Flammable liquid storage cabinets are very common. These cabinets are designed to withstand a fire for two hours.

The cabinets are provided with a vent opening on the top and bottom to provide active ventilation of the vapours.

If active ventilation is not used, keep the vents sealed.

Use administrative controls

Engineering controls are preferable to administrative controls because they do not rely or require human intervention.

Administrative controls are controls over your affective behavior.

They consist of rules which explain what you are allowed to do and how you must do it.

Administrative controls can be institutional policies on numerous subjects and can include procedural controls (standard operating procedures).

Another administrative control is allowable exposure time.

But it must be remembered that both elimination and engineering controls are usually more preferable than administrative controls.

Use personal protective equipment

The last step in reducing risk is to wear personal protective equipment.