Workplace Health and Safety
Derrick A. Denis is the Vice President of Indoor Air Quality for Clark Seif Clark, Inc. (CSC), a consulting firm in Phoenix, Arizona, specializing in indoor air quality. He received an undergraduate degree in environmental science and is the President of the Phoenix Chapter of the Indoor Air Quality Association. Comments can be reached by email at firstname.lastname@example.org or by phone at (480) 460-8334.
Ms. Shaw is a professional environmental consultant for Clark Seif Clark, Inc. She works in the capacity of Industrial Hygienist in the Indoor Environmental Quality Division based out of CSC's Phoenix, Arizona office. Ms. Shaw manages and performs a variety of environmental projects including indoor environmental quality investigations and project management. Additionally, she provides appraisal hearing and litigation support, as well as develops and facilitates health and safety training that is specific to client needs.
Melissa K. Debnar is an indoor air quality investigative specialist for Clark Seif Clark, Inc. (CSC). She received a master degree in environmental resources and is a member of the Indoor Air Quality Association.
Special thanks to C&E Services of Phoenix, Arizona and RSG Technologies, Inc.
Let us set the stage for a possible, but realistic scenario. A dry ice blasting field operator has performed multiple successful projects without a hitch. On this peculiar day, the operator is performing the same duties he normally does, but today something is different. The operator stops in the middle of the job and exits the contained work area.
A collegue of the operator asks, "What's wrong?"
The operator mutters, "I feel dizzy and light headed." What could have caused these symptoms?
This is where we, Clark Seif Clark, Inc. (CSC), become involved in the project. As indoor environmental health and safety professionals, we often write specifications for remediation work to be performed by others. Our challenge is to balance worker and bystander safety with time-frame constraints and financial considerations.
It is exciting to see creatively applied existing technology and newly developed technology applied to remediation projects. Dry ice blasting is an existing technology with some recent new advances that are becoming more and more popular with mold and lead-based paint (LBP) remediation contractors. Dry ice blasting is also being utilized to remove runway rubber buildup, to clean electrical equipment, and to restore smoke damaged building materials.
It is the opinion of the authors that dry ice blasting can be performed safely. In order to safely perform remediation using dry ice blasting techniques, one must fully understand the health and safety hazards of both the material being remediated (mold, LBP, etc.), the hazards unique to dry ice blasting, and any synergistic hazards of combining the two.
Dry ice blasting is being marketed to decreased downtime, reduced or even elimination of solvents and reduced waste disposal.
Tina Moore's, marketing specialist at Cold Jet LLC., 2006 article, Chilling Out: How Mold Remediators Use Dry Ice in Mold in Moisture Management Magazine, mentions that carbon dioxide build-up can be hazardous in closed areas and the solution is to monitor carbon dioxide and provide a negative air-set up.
We want to know: How many air changes are needed to control carbon dioxide levels and maintain oxygen levels? What levels of carbon dioxide are dry ice blasting operators exposed to and should carbon dioxide monitoring be part of dry ice blasting? These are some of the questions CSC has put forth.
How dry ice leads to elevated carbon dioxide...
Dry ice blasting utilizes frozen (-109° F or -78°C) carbon dioxide pellets. "The dry ice is accelerated in a pressurized air stream to impact the surface that is to be cleaned or prepared," states RSG Technologies, Inc., a manufacturer of dry ice blasting equipment. The media then "vaporizes upon impact with the surface," as described by RSG Technologies, Inc. Vaporizing, or sublimation, described here means that the frozen carbon dioxide pellets become carbon dioxide gas on impact. It is estimated that one pound of dry ice will expand to approximately 8 cubic feet following sublimation.
Carbon dioxide in ambient air ...
Natural sources of atmospheric carbon dioxide include volcanic outgassing, the combustion of organic matter, such as fossil fuels for heating, power generation and transport, as well as the respiration processes of living aerobic organisms. The carbon dioxide level in outdoor ambient air is around .035 %, or 350 parts per million (ppm).
Carbon dioxide gas is odorless and colorless, so elevated levels cannot be detected visually or by odor. When carbon dioxide is inhaled at high concentrations, it produces a sour taste and a stinging sensation in the nose and throat. You may have experienced this sensation if you have ever tried to suppress a burp after drinking a carbonated beverage. The sour taste and stinging are caused by carbon dioxide dissolving in the mucus membranes and saliva, forming a weak solution of carbonic acid.
Carbon dioxide exposure...
In an indoor atmosphere, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 62-2001 recommends carbon dioxide be maintained at less than 700 parts per million (ppm) above the outdoor readings for the comfort of most occupants. The American Council for Governmental Industrial Hygienists (ACGIH) time-weighted average (TWA) for carbon dioxide exposure is 5,000 ppm. Occupational Safety and Health Administration (OSHA) places the carbon dioxide exposure limit at 10,000 ppm for an 8-hour TWA and at 30,000 ppm for a 15-minute short-term exposure limit (STEL). NIOSH's STEL for 15 minutes is 3% or 30,000 ppm. The NIOSH "immediately dangerous to life or health" (IDLH) level is 4% or 40,000 ppm. Also, the NIOSH's permissible exposure limit (PEL) for carbon dioxide in the workplace is 0.5%, or 5,000 ppm for a 40-hour workweek. The primary control method for reducing carbon dioxide in many work environments is simply to ventilate affected areas with outdoor. In Managing Indoor Air Quality, H.E. Burroughs and Shirley J. Hansen describe how carbon dioxide is "used to define a minimum limit of outdoor air needed to ventilate a building." However, there is a lack of data regarding carbon dioxide and the minimum required ventilation during blasting events, as well as operator exposure levels during dry ice blasting. Therefore we wanted to discover what carbon dioxide levels are being produced during a dry ice blasting episode.
CSC was able to begin monitoring carbon dioxide levels with the cooperation of C&E Services, who provided the operators, and their newly purchased RSG Technologies, Inc. dry ice blasting equipment.
CSC performed preliminary carbon dioxide monitoring during a dry ice blasting project with C&E services. This project's parameters were not designed for experimental purposes, so monitoring was performed in a "real-life" scenario. CSC's goal was to determine the carbon dioxide levels before, during, and after dry ice blasting at multiple locations around the project, including areas at the blast operator's location, throughout the contained negative pressure enclosure, opposite critical barriers to the enclosure, near the air filtration device exhaust, and outdoors away from the project location.
The project took place in a two-level residence. The contained work area was on the ground level and measured approximately 9,287 cubic feet (ft3). Critical barriers constructed of plastic sheeting and tape separated the ground floor work area from the balance of the ground floor. The plywood subfloor and wooden floor finish separated the ground floor from the second floor. There were four HEPA-equipped negative air machines operating inside the containment during the dry ice blasting event. Each negative air machine was exhausting 2,000 cubic feet per minute (cfm) of air from the containment to the exterior north side of the containment. The unfiltered makeup air was entering through an open door on the southeast side of the containment.
To monitor the carbon dioxide levels, CSC used custom-built ventilation monitoring stations to record readings in several location inside and outside the containment, HOBO® Onset computer corporation personnel monitoring device to record measurements on the dry ice operator, and a real-time measurement device, Engelhard Model 7001 Carbon Dioxide Monitor for grab samples.
CSC's custom-built ventilation monitoring stations consist of an electronic data recorder and a non-passive, non-interactive, non-dispersive infrared (NDIR) carbon dioxide monitor. All stations included temperature and humidity sensors. The stations exceed four air exchanges per minute. The data collected was recorded every 5 minutes.
The HOBO® device on the operator collected temperature, relative humidity, and carbon dioxide every 30 seconds.
The Engelhard Model 7001 carbon dioxide monitor detects levels from 0 to 10,000 ppm, however since CSC attached the carbon dioxide monitor to the ventilation monitoring stations and the HOBO, the carbon dioxide maximum voltage output was 4,000 ppm. However for the real-time reading we were able to document measurements up to and equal to 10,000 ppm.
We wanted to sample as many locations inside and outside the containment as possible, in order to determine which locations would represent the levels the dry ice operator would be exposed to. We placed eight ventilation monitoring stations in the following locations:
- A baseline at a residence located ~ 1 mile away from the containment residence,
- Two outdoors, one about 50 feet and one about 19 feet from the negative air machines exhaust ducts on the north side of the residence
- Two inside the residence, but outside the containment, one on the ground floor about 12 feet due east of the containment and one on the second floor directly above the enclosure
- Three inside the containment, one at ground level, one at breathing height, and one at the ceiling.
We placed a dosimeter device on the operator at the breathing zone to record the blast technician's carbon dioxide exposure concentrations during the dry ice blasting operation. We used and HOBO® and the Engelhard Model 7001 carbon dioxide monitor to record real time measurements.
- Blasting lasted for approximately one hour, however the dry ice operator was not consistently blasting.
- Real-time measurements ranged from 542 ppm carbon dioxide outside the containment exhaust prior to the operation of the dry ice blasting to greater than 10,000 ppm approximately six minutes after the start of the dry ice blasting and stayed at or above 10,000 ppm throughout the blasting project.
- The ventilation monitoring stations maxed out at 4,000 ppm at multiple locations during the operation of the dry ice blasting, including outside the containment exhaust and inside the containment.
- It took approximately 1.5 hours after the blasting concluded for the carbon dioxide levels outside the containment exhaust area to return to the pre-dry ice blasting levels.
In conclusion, the carbon dioxide realtime meter reached at least 10,000 ppm throughout the duration of the blasting. Therefore, adequate ventilation is needed and that number should be made available for the personnel using the equipment. To assure adequate ventilation monitoring of CO2 levels should be a integrate part of the dry ice blasting process. Carbon dioxide is known to displace oxygen. It is estimated that one pound of dry ice will expand to approximately 8 cubic feet.
Clark Seif Clark would like to design a controlled study with the help of remediation contractors and dry ice blasting manufacturing companies to answer questions such as:
- What are the maximum carbon dioxide levels reached inside a contained work area during ice blasting? Our measurements were limited to 10,000 ppm with the real-time monitor and 4,000 ppm with the data recording devices.
- Does the expanding gas of carbon dioxide produce positive pressure that will lead to localized containment breachs?
- How many air changes per hour (AC/H) are needed to safely operate dry ice blasting equipment in an enclosure?
- What are the visibility limitations?
- How much are oxygen levels reduced?
Then ultimately, CSC would like to answer further questions about dry ice blasting operations: What hazards inherent to dry ice blasting must be considered in your jobsite safety plan?
- Hearing loss
- From noise generated by the blast gun
- From noise generated by the compressor
- Eye injury
- From deflected blast media (dry ice) projectiles
- From dislodged blast surface material
- Slips & Falls
- From limited visibility due to dense airborne particulate
- From loose hoses on the floor of the work area
- From limited visibility from the wearing respiratory and eye protection
- Lift injuries
- From mishandling the heavy equipment and supplies
- Freezing Skin
- From mishandling dry ice
- From mishandling cold blast equipment
- From exposure to work environment artificially cooled by dry ice
- From low outdoor air temperatures being drawn into the work area
- From wind chill from elevated air flow
- From handling dry ice
- From oxygen displacement by sublimation of dry ice solid into carbon dioxide gas
- Carbon dioxide overexposure
- From sublimation of dry ice solid into carbon dioxide gas
- Poisoning by carbon monoxide
- From combustion byproducts drawn into the compressor air stream and released at the blast site
- From compressor exhaust being drawn into the enclosure make-up air stream
- Containment breaches
- From pockets of positive pressure created by sublimation of dry ice solid into carbon dioxide gas
- From penetration of the enclosure by dry ice blast media or compressed air