Significant New Alternatives Policy Program

Refrigeration and Air Conditioning Sector

Risk Screen on Substitutes for HCFC-22 in Cold Storage Warehouses.

Substitute: Carbon Dioxide (CO2)

This risk screen does not contain Clean Air Act (CAA) Confidential
Business Information (CBI) and, therefore, may be disclosed to the
public.

INTRODUCTION

Ozone-depleting substances (ODS) are being phased out of production in
response to a series of diplomatic and legislative efforts that have
taken place over the past decade, including the Montreal Protocol and
the Clean Air Act Amendments of 1990 (CAAA).  The U.S. Environmental
Protection Agency (EPA), as authorized by Section 612 of the CAAA, is
developing a program to evaluate the human health and environmental
risks posed by alternatives to ODS.  The main purpose of EPA's program,
called the Significant New Alternatives Policy (SNAP) Program, is to
identify acceptable and unacceptable substitutes for ODS in specific end
uses.  

EPA’s decision on the acceptability of a substitute is based largely
on the findings of a screening assessment of potential human health and
environmental risks posed by the substitute in specific applications. 
EPA has already screened a large number of substitutes in many end uses
within all of the major ODS-using sectors, including refrigeration and
air conditioning, solvent cleaning, foam blowing, aerosols, fire
suppression, adhesives, coatings and inks, and sterilization. The
results of these risk screens are presented in a series of Background
Documents that are available in EPA's docket.

The purpose of this report is to supplement EPA’s Background Document
on the refrigeration and air conditioning sector (EPA 1994) (hereinafter
referred to as the Background Document) by adding to the list of
potential substitutes for specific end-uses of HCFC-22 in this sector. 
The proposed end-use considered in this analysis is chillers in cold
storage warehouses.  The specific proposed HCFC-22 substitute examined
in this report is carbon dioxide (CO2, or R-744).   The chillers and
their CO2 charge are expected to be located external to the building in
which they are used.  

This risk screen addresses potential asphyxiation and toxicity risks to
workers during equipment manufacture and use.  Consumer or general
population exposures are not expected to occur.  Carbon dioxide is not
flammable, so a flammability analysis was not conducted.  The reader is
referred to the Background Document for a detailed discussion of the
methodologies used to conduct this risk screen.

Section 2 of this report summarizes the results of the risk screen for
the proposed substitute.  The remainder of the report is organized into
the following sections:

Section 3: Atmospheric Assessment

Section 4: Asphyxiation Assessment

Section 5: Toxicity Assessment

Section 6: Volatile Organic Compound Assessment 

Section 7: References

SUMMARY OF RESULTS

Carbon dioxide is recommended for SNAP approval for use in cold storage
warehouse chillers.  EPA's risk screen indicates that the use of the
proposed substitute will be less harmful to the atmosphere than the
continued use of HCFC-22.   No significant asphyxiation or toxicity
risks to workers are expected.  EPA recommends that American Society of
Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standards
15 and 34 be followed, as well as Chapter 11 (“Refrigeration”) of
the International Mechanical Code.

ATMOSPHERIC ASSESSMENT

This section presents an assessment of the potential risks to
atmospheric integrity posed by the use of carbon dioxide in cold storage
warehouses.  The ODP, GWP, and atmospheric lifetime (ALT) of the
proposed substitute are presented in   REF _Ref175036149 \h  Table 1 . 
The substitute is substantially less harmful to the ozone layer and has
less climate impact than HCFC-22.

Table   SEQ Table \* ARABIC  1 .  Atmospheric Impacts of Carbon Dioxide
Compared to HCFC-22.

Refrigerant	Ozone Depleting Potential (ODP)	Global Warming Potential
(GWP)	Atmospheric Lifetime years (ALT)

Carbon Dioxide	0 a	1 a	NA b

HCFC-22	0.055 c	1,500 d	12 c

a Carbon Dioxide SNAP Submission (IPS 2008).

b NA = Not Available; Meehl et al. (2007) report that a lifetime for CO2
“cannot be defined.”

c Available at: http://www.epa.gov/ozone/ods.html.

d IPCC, Second Assessment Report (1996).

ASPHYXIATION ASSESSMENT

Use of carbon dioxide in this proposed end-use is not expected to pose a
significant risk of asphyxiation to workers.  As the substitute is
proposed for use in a chiller whose charge is external to the building
in which it is used, leakage from the top of the building into the
warehouse is unlikely.  Subsequently, asphyxiation due to accidental
release of the substitute into the warehouse is not expected for the
proposed end-use.  To ensure that leakage into the warehouse does not
occur, it is recommended that the building be designed to prevent this,
which would be the norm, as cold storage facilities are designed to be
airtight and to segregate storage space from mechanical space.

While workers could be exposed to the substitute during installation or
maintenance of the system, the risk of asphyxiation is minimal as they
will be outside.  To minimize the potential for leaks during
installation and maintenance, it is recommended that workers receive
proper training.   Also, because carbon dioxide is denser than air there
is the potential for pooling of CO2 in low-lying spaces which could
inadvertently cause an oxygen-deficient atmosphere.  As the system will
be located outside, natural airflow will likely disperse any CO2.which
accumulates; however it is recommended that those installing the
chillers be aware that CO2 can accumulate in low-lying areas.   

TOXICITY ASSESSMENT

5. 1.  Toxicity Reference Values

To assess potential health risks from exposure to this substitute in
cold storage warehouses, EPA identified the relevant toxicity threshold
values for comparison to modeled exposure concentrations for different
scenarios.  For the occupational exposure analysis, potential risks from
chronic and acute worker exposure were evaluated by comparing exposure
concentrations to available occupational exposure limits.  Occupational
exposure limits are typically established for either an eight-hour or
ten-hour time period for long-term exposure, or for a 10 to 30-minute
period for short-term exposure, as shown in   REF _Ref222734171 \h  \*
MERGEFORMAT  Table 2 .    REF _Ref225834278 \h  \* MERGEFORMAT  Table 3 
provides definitions for acronyms used in   REF _Ref222734171 \h  \*
MERGEFORMAT  Table 2 .  EPA’s approach for identifying or developing
these values is discussed in Chapter 3 of the Background Document. 

Table   SEQ Table \* ARABIC  2 .  Toxicity Levels of Carbon Dioxide.

	Long-term Exposure

ppm	Short-term Exposure

ppm

Carbon Dioxide	5000a 

(OSHA PEL/NIOSH REL)	30,000a (NIOSH REL-STEL)

40,000a (IDLH)

a  http://www.cdc.gov/Niosh/npg/npgd0103.html

Table   SEQ Table \* ARABIC  3 .  Explanation of Toxicity-Related
Acronyms. a

Organization 	Definition

OSHA	Occupational Safety and Health Administration

NIOSH	National Institute for Occupational Safety and Health

Exposure Limit	Definition	Explanation

IDLH	Immediately Dangerous to Life and Health	If exposed to this
concentration, room occupants are expected to be able to escape the room
within 30 minutes without experiencing escape-impairing or irreversible
health effects.

PEL	Permissible Exposure Limit	This is an 8-hour time-weighted average
exposure limit set by OSHA. 

REL- STEL	Recommended Exposure Limit - Short-term exposure limit	This is
a 15-minute time-weighted average exposure limit set by NIOSH.

aAll information in this table taken from EPA (1994).

5. 2.  Occupational Exposure 

As discussed in Section   REF _Ref232231072 \r \h  4 , significant
exposure to carbon dioxide in this end-use is not expected for workers
as the substitute is proposed for use in a chiller whose charge is
external to the building in which it is used.  Further, exposure is not
expected during manufacture as the system would be charged with carbon
dioxide on-site during installation, not at the manufacturing facility.

To ensure that leakage into the warehouse during installation or
maintenance does not occur, it is recommended that the building be
designed to prevent this.   Additionally, while workers could be exposed
to the substitute during installation or maintenance of the system,
toxicity risks are minimal as workers will be outside.  It is
recommended that workers receive proper training to minimize the
potential for leaks during installation and maintenance. 

5. 3.  Consumer and General Population Exposures

Consumer and General Population modeling was not performed because
exposures to the proposed substitute are not expected for these groups.

VOLATILE ORGANIC COMPOUND (VOC) ASSESSMENT

Carbon dioxide has been exempted as a VOC under the CAA (40 CFR 51.100).


REFERENCES

EPA. 2000.  Carbon Dioxide as a Fire Suppressant: Examining the Risks. 
February 2000. Available at: <
http://www.epa.gov/Ozone/snap/fire/co2/co2report.html>.

EPA. 1994.  Significant New Alternatives Policy Technical Background
Document:  Risk Screen on the Use of Substitutes for Class I
Ozone-depleting Substances: Refrigeration and Air Conditioning. 
Stratospheric Protection Division.  March 1994.

ICF. 1997. Physiological Effects of Alternative Fire Protection Agents -
Hypoxic Atmospheres Conference. Stephanie Skaggs prepared the
proceedings of the conference held May 22, 1997 in New London, CT.

Integrated Packaged Systems (IPS). 2008. Significant New Alternatives
Policy Program Submission to the United States Environmental Protection
Agency.  December 2008. 

Meehl, G.A., T.F. Stocker, W.D. Collins, P. Friedlingstein, A.T. Gaye,
J.M. Gregory, A. Kitoh, R. Knutti, J.M. Murphy, A. Noda, S.C.B. Raper,
I.G. Watterson, A.J. Weaver and Z.-C. Zhao.  2007. Global Climate
Projections. In: Climate Change 2007: The Physical Science Basis
.Contribution of Working Group I to the Fourth Assessment Report of the
Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M.
Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller
(eds.)]. Cambridge University Press, Cambridge, United Kingdom and New
York, NY, USA.

 This has been a concern for carbon dioxide fire extinguishing systems
and is addressed in several fire protection regulations (EPA 2000).

	Page   PAGE  3 	   July 2, 2009

