Moderate Risk Waste photo identifier


What is expected for sufficient ventilation in MRW fixed facilities? *

In general, consolidation of MRW triggers the need for mechanical ventilation. Examples of air contaminants that should be ventilated include airborne dust from absorbents during lab packing and toxic and flammable vapors during bulking operations. Compressed gas containers, such as butane and propane bottles, may also need ventilation.

Whether consolidation of MRW takes place or not, consultation with the Washington Department of Labor and Industries (L&I) and local fire officials is necessary to determine the needs at a specific facility. L&I gives guidance on controls that provide enough ventilation to prevent worker exposure to hazardous substances. Fire officials provide direction on fire and explosion prevention. L&I has confidential industrial hygiene consultation services available to employers at no cost.

Though you need to contact L&I and local fire officials, this document provides some guidance. The only numeric measure in chapter 173-350 WAC for MRW facilities states, “[f]lammable or explosive gases do not exceed ten percent of the lower explosive limit in the area where MRW is handled.” Adherence to L&I and local fire codes should prevent reaching this concentration.

Bulking of Toxic or Flammable Substances

For facilities that bulk toxic and flammable substances (combining oil-based paint, thinners, solvents into a drum; evacuation of spray paint aerosol cans and propane containers), the following are L&I’s best management practices to keep concentrations below permissible exposure limits:
  1. Mechanical ventilation in areas where workers bulk materials.
  2. Full enclosure of drums that are being bulked into.

Natural ventilation is unpredictable, both in direction and in airflow volume. This makes it nearly impossible to set up reliable work practices to minimize exposure. Mechanical ventilation and use of a hood provides consistent airflow to keep harmful substances from employee breathing zones and prevent an accumulation that could lead to fire or an explosion.

L&I does not allow use of respirators instead of mechanical ventilation. Respirators may be used to control worker exposure only when ventilation is not feasible, when it does not lower the air contaminant levels below their permissible exposure limits or in emergencies.

Also for areas where workers bulk flammables, section 7903. of the 2000 Uniform Fire Code (there are newer versions) states that:

"[c]ontinuous mechanical ventilation shall be provided at a rate of not less than 1 cubic foot per minute per square foot of floor area over the design area. Provisions shall be made for introduction of makeup air in such a manner to include all floor areas or pits where vapors can collect. Local or spot ventilation shall be provided when needed to prevent the accumulation of hazardous vapors."

Storage of Toxic or Flammable Substances

For ventilation of toxic or flammable liquid storage area, an L&I rule, WAC 296-24-33009, states:

"Every inside storage room shall be provided with either a gravity or a mechanical exhaust ventilation system. Such system shall be designed to provide for a complete change of air within the room at least six times per hour. If a mechanical exhaust system is used, it shall be controlled by a switch located outside of the door. The ventilating equipment and any lighting fixtures shall be operated by the same switch. A pilot light shall be installed adjacent to the switch if Class I flammable liquids are dispensed within the room. Where gravity ventilation is provided, the fresh air intake, as well as the exhaust outlet from the room, shall be on the exterior of the building in which the room is located.”

Ventilation Equipment

HHW Spot Ventilation

There are two basic types of ventilation - area ventilation and local exhaust (spot) ventilation. Area ventilation exchanges air in the building or areas of a facility. Spot ventilation removes contaminants at the point of generation, so is the most appropriate type in areas where bulking occurs. It is also effective in removing dust particles.

Spot ventilation uses a fixed exhaust register or a movable, articulated-arm ventilator (see image at left). Place the ventilator as close as possible to the air contaminant source to remove the hazard. Orient it to draw air away from the worker’s breathing zone and not through the worker’s breathing zone.

A qualified ventilation engineer or firms specializing in this field and L&I and local fire officials should approve ventilation design. See L&I's ventilation guideline for some basics.

Summary of Standards
Standard origin Numeric performance or design standard Standard or citation
Solid Waste Rule Less than 10 percent LEL for flammable vapors WAC 173-350-360 (6)(a)(xi)
Labor and Industries List of air contaminant concentration limits WAC 296-841-20025
Labor and Industries More than six complete air changes per hour WAC 296-24-33009
Uniform Fire Code One cubic foot of air per minute per square foot of design floor area Section 7903. UFC

* Note: The answers provided to Frequently Asked Questions are guidance for implementing WAC 173-350-360. Following this guidance is not a requirement of operation or design for MRW facilities, as facilities may meet regulatory requirements through other means. Local Health Departments should be consulted to determine what will be sufficient to meet the regulatory standards.