ASHRAE 15, Carrier discussion

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VOLUME FOUR NUMBER ONE

HVAC

(SUPERSEDES VOLUME ONE NUMBER ONE)

A N S W E R S

F O R

T H E

C O N S U L T I N G /

S P E C I F Y I N G

C O M M U N I T Y

In this issue...
ASHRAE Standard 15-1994 and its implications for mechanical room design should be required reading for every HVAC professional, especially since it is now being used to write local municipal building codes. In the last several years, the standard has been revised to address the rapid changes regarding refrigerant phaseouts, alternative refrigerants and the safe installation and operation of mechanical refrigeration systems. This issue of Analysis discusses the standard and its recent addenda. It is intended not as a substitute for reading the standard, but as a guide to assist in understanding and applying ASHRAE 15.

ASHRAE 15-1994: Implications for Mechanical Room Design — 2001 Update
Introduction
new alternative refrigerants that were already appearing in the marketplace. Thus, ASHRAE 15 was revised in 1992 and again in 1994, followed by several addenda in the last two years. The current standard is now being used to formulate municipal codes for the safe installation and operation of mechanical refrigeration systems throughout the United States and beyond. written in code language so it could be adopted nearly verbatim, if desired, by model code associations. The primary goal of the standard is to mitigate safety risks to the environment, to mechanical room operators and, ultimately, to the general public. With the introduction of alternative refrigerants such as HCFCs, HFCs and mixtures of refrigerant compounds known as blends, new refrigerant safety classifications were added under ASHRAE Standard 34-1992, “Number Designation and Safety Classification

First issued as a safety code (Standard B9) in 1930, the same year that CFC (chlorofluorocarbon) refrigerants were introduced in the United States, ASHRAE Standard 15 has undergone unusually rapid change over the last decade. During this same period, the air conditioning industry and its customers have been faced with The Clean Air Act Amendments of 1990. These amendments legislate the phaseout of CFC production by the end of Educate Your Customers: 1995, and the end of new The highlights of the revised production equipment ASHRAE 15-1994 are using HCFCs (hydrochlorosummarized in Carrier’s fluorocarbons) by 2020. SYNOPSIS newsletter, which Although the regulations is written specifically for permit the responsible building owners and managers. To download copies of SYNOPSIS, use of these refrigerants, intentional venting is strictly Vol. 4, No. 1. at no charge, visit our web site www.carrier.com, prohibited for all refrigerclick on Commercial/Industrial ants, including HFCs Heating and Cooling Systems (hydrofluorocarbons). and see Newsletter under At the time of this Resource Center. legislation, neither ASHRAE nor ARI safety standards had been updated to address the

Code Compliance and Safety
ASHRAE Standard 15-1994 was intentionally

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of Refrigerants.” Allowable exposure limits for the various refrigerants range from a low of 10 ppm (parts per million) to a cap of 1,000 ppm. Some blends comprise one or more flammable compounds, introducing yet another safety concern. Using ASHRAE 34-1992 as a starting point, ASHRAE 15-1994 and its subsequent addenda have been written to help professionals minimize risk and promote safety. Because ASHRAE 15-1994 is written in code language, it can be difficult to read and understand.

Mechanical Room Safety Check
For many building owners, mechanical rooms are virtually unknown areas of their property. “Out of sight, out of mind” rings true in far too many cases. Most owners understand only that the equipment in the mechani-

cal room supplies chilled water for air conditioning. Equipment may be 10, 20, 30 or even 50 years old — each unit installed to comply with the codes of the day. Given the new ASHRAE standard and the approaching HCFC production phaseout, now is the right time for owners, operators and engineers to conduct a complete mechanical room safety check and review potential liability problems. The following checklist highlights the many important items to look for (Figure 1). Are exhaust outlets located near inlet vents? Safety relief devices on chillers are typically vented to the outside, most often through the roof. It is important to know how close this vent is to the air intakes on the roof, and to insure that there is at least 20 feet between them. Are roof drains vulnerable to collecting refrigerant? If you lose refrigerant from

an exhaust outlet and it vents a few feet above a flat, curbed roof, the refrigerant could very well spread across the roof and find the first exit. This would most likely be down the roof drains, most of which lead directly to a sewer system. Where does the purge vent? A conventional purge loses three to 20 pounds of refrigerant for every pound of non-condensible air it removes from the system. Most vent directly into the mechanical room which may invite unnecessary problems. All purges should vent outside. If high efficiency purges are applied, it is best to specify them in accordance with the new ARI Standard 580-2000. Where are safety rupture disk outlets located? On a CFC-11 or HCFC-123 chiller, the safety device is a thin carbon rupture disk that is meant to shatter at 15 psig, allowing the charge to safely exit the system. These disks

FIGURE 1

Mechanical Room Safety Check

are often vented through the roof or side of the building. Yet in climates with warm days and cool nights, moisture often condenses in the pipes before it can evaporate off. Then, along with the rust and other accumulations in the pipe, moisture ends up “sitting” on the rupture disk. Over time, this may corrode the joint and result in failure of the seal. Are rupture lines the right size and length? For convenience, safety devices sometimes run into a common header if they have common refrigerants. Chillers with different headers should never share common headers as they operate at different pressures. Also, an improperly sized header can exacerbate problems in an emergency, when the discharge capacity of safety lines is put to the test. Are chiller drain valves secured? More often than not, chiller drain valves are an easy way for an inexperienced technician to get into trouble. Make sure the valves are locked off. Is access to the mechanical room restricted? Most mechanical rooms have neither a door nor any other barrier to restrict people from entering unsupervised. If there is a fire door, it is typically left open. Not only are mechanical rooms potentially hazardous places, but they contain systems critical to a building’s operation. Restricting access is only common sense. The mechanical room door should have a tight seal to isolate the room in case of an emergency. The entry restriction should apply to all personnel not trained in emergency procedures relating to mechanical room operation.

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Are there any pits (low areas) in the mechanical room? Check the condition of any pits or other areas below floor level. They may house a host of unwanted chemical residues such as acids, spilled refrigerant, cleaning solvents, etc. Where do the floor drains empty? Most floor drains were constructed to handle wash water and empty into the sewer system. But if your chiller and occupied space share the same floor, they may also share drainage systems — and drainage traps can dry out. Check to see if drains in the occupied space (i.e., in restrooms) are connected to those in the mechanical room. Imagine losing a full charge and “finding” it in a restroom! These are some of the many factors to consider when evaluating the safety of your mechanical room. And when assessing a property, the condition of the mechanical room and its equipment should be significant considerations in your purchasing decision.

submittals and service agreements.

Equipment Design
Manufacturers’ labels reference compliance with the standard.

project cost, depending on the room’s age and location. This expense should be factored into the refrigerant planning cost analysis.

Building Code Compliance
The major U.S. building code jurisdictions are currently in various stages of incorporating ASHRAE 151994 into their model codes. These updated codes will ultimately be passed down to state and municipal levels. For this reason, it is always a good idea to meet with your building inspector before mechanical room changes are made. Find out what’s happening to codes in your area, then decide how to proceed.

Safety Stewardship
Professionals who can prove that they have gone to the furthest extent possible to promote safety will minimize their legal liability. This is true for all professionals in the HVAC business, including property developers, consulting engineers, contractors and others.

Mechanical Room Changes
The CFC and HCFC refrigerant production phaseout has raised the critical issue of what to do with existing chillers. Each possible solution — containment, conversion or replacement — brings with it new concerns. It is particularly important to understand that if the type of refrigerant in a chiller is changed or if the chiller itself is replaced, ASHRAE 15-1994 applies. Section 5.3 of the standard reads: “A change in the type of refrigerant in a system shall not be made without the notification of the authority having jurisdiction, the user and due observance of safety requirements. The refrigerant being considered shall be evaluated for suitability.” On the other hand, the addition of containment devices, i.e., high efficiency purges and back-up relief valves, to your existing equipment does not trigger application of the standard. The cost of mechanical room upgrades is typically 11 to 13% of the total chiller conversion/replacement

ASHRAE 15-1994 Overview
A walk through ASHRAE 15-1994 begins with a general look at the property in question and its mechanical refrigeration systems. The type of occupancy — institutional, public assembly, residential, commercial, large retail, industrial or mixed occupancy — determines which system application rules apply. The next step is to identify the type of refrigerant system involved — direct or indirect. In direct systems, the chiller sends refrigerant out into the cooling coils near the occupied spaces. In indirect systems, refrigerant runs through the chiller only, and chilled water in a separate circuit produces the cooling in the airside system. Indirect system types include double indirect open spray systems, indirect closed systems and indirect vented systems (all described in ASHRAE 15-1994). The probability of refrigerant reaching the occupied

spaces depends in large part on the type of system involved. To characterize the degree of risk, ASHRAE 15-1994 introduces the broad categories of “low-probability” and “high-probability” systems. Low-probability systems are those in which the leakage of refrigerant from a failed component cannot enter the occupied spaces. Examples include indirect closed systems; double indirect systems; and indirect open spray systems where the secondary coolant pressure exceeds refrigerant pressure. Conversely, high-probability systems are described in the standard as those in which leakage of refrigerant from a failed component will enter the occupied spaces. High-probability systems include all direct systems, as well as indirect open spray systems where the refrigerant pressure always exceeds the secondary coolant pressure.

Refrigerant Classifications
In its 1992 update, ASHRAE 15 refined the way refrigerants are classified for toxicity (Figure 2). Refrigerant compounds were divided into two groups, “low-toxicity” and “high-toxicity,” designated by the letters A and B. Refrigerants with allowable exposure limits (AELs) of more than 400 ppm are classified as type A (lower toxicity) refrigerants, and those with AELs of less than 400 ppm are type B (higher toxicity). ASHRAE 15-1994 further classifies refrigerants according to their degree of flammability: type 1 — no flame propagation; type 2 — low flammability; and type 3 — high flamma-

Applying ASHRAE 15-1994
What is your compliance obligation to ASHRAE 15-1994? If you are a professional engineer, a manufacturer or an owner, you are liable under the standard simply by being aware of it. Compliance with ASHRAE 15-1994 is also mandated in the following situations.

Contracts
The specification that equipment and service “must be in compliance with the latest ASHRAE 15” has become standard contract language for installation

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FIGURE 2

ASHRAE 34 Safety Group

High Flammability

A3 Propane

B3

Low Flammability

A2 R-142b, 152a

B2 Ammonia

No Flame Propagation

A1
R-11,12,22, 114,500,134a
Lower Toxicity

B1 R-123, SO2
Higher Toxicity

bility. Ammonia, for example, is considered a low-flammability refrigerant, while refrigerants like HCFC-22 and HFC-134a have no flame propagating properties. It should be noted that R-600a and R-1270a, found in some blends, are flammable and would fall into class 3 if they were used as single compounds. Although their flammability is mitigated when they are mixed into a blend, flammability may still be an issue in leak situations. When blends leak, the highestpressure compound exits first, mixed with the next highest-pressure compound. The lowest-pressure compound, then, is likely to be left in the vessel, and in this state the mixture may be flammable. A recent addendum to ASHRAE 341992 reflects the fact that the flammability classification of a blend may change as it leaks. The addendum states that a blend will be classified to reflect the highest potential flammability or toxicity of its components, as shown in Figure 3.

Complying With ASHRAE 15-1994
Here are some of the primary issues to consider when examining a mechanical equipment room for compliance with ASHRAE 15-1994.

Maximum Refrigerant Without a Mechanical Room
Table 1 of the standard lists allowances for all refrigerants in pounds of refrigerant per 1,000 cu. ft. of occupied space. Often misinterpreted, these figures represent the maximum refrigerant levels allowable without a separate mechanical equipment room. If you have more than the allowable amount of refrigerant, your system must be housed in a separate mechanical room. Table 1 is often misinterpreted in an effort to exempt or somehow restrict the application of large chillers. Simply put, Table 1 requires almost all commercial chillers to be in a “machinery room” as a result of their relatively high refrigerant levels. The intention of

Table 1 and the restriction of refrigerant quantities is to allow small commercial refrigeration units to be used in “occupied spaces.” When the rules in ASHRAE 15 refer to Table 1 of the standard, you must calculate the amount of refrigerant per 1,000 cu. ft. of occupied space for the application. Determine the amount of refrigerant in the largest single unit of the system or the largest refrigeration circuit. Then, determine the occupied space and do the calculation. Different calculations must be used for unventilated and ventilated spaces. • Unventilated Occupied Spaces: In a hotel room, for example, the air conditioning unit is typically a PTAC unit. The room houses the refrigeration unit and there is no special ventilation — it is considered an “unventilated occupied space.” If the hotel had a large chiller instead, the volume of the occupied space would be the building the chiller serves. In the case of the PTAC unit, the allowable refrigFIGURE 3

erant quantity in Table 1 would be below the limit. For a chiller, the volume would exceed any of the limits and would require a “machinery room.” • Ventilated Occupied Spaces: Ventilated space is where a refrigeration unit may have the evaporator or condenser coil located directly within the duct system that supplies the occupied space. In this case, Table 1 would consider the occupied space to be the entire space served by the duct system. There are some restrictions, such as 1) Where the air flow in the space can be reduced below 25% of the design, that space must not be considered in the calculated total space volume; and 2) Plenum space cannot be included unless it is continuous and part of the return air system. Let’s look at an example. Figure 4 shows a mixed-occupancy facility that uses a 20-ton packaged rooftop unit (classified as a high probability system) containing 20 lbs. of R-22

ASHRAE 34 Safety Group Examples Of Blend Refrigerant Classification

High Flammability

A3

B3

Low Flammability

A2 R-406*

B2

No Flame Propagation

A1
Lower Toxicity

B1
Higher Toxicity

*R-406 = 55% R-22, 4% R-600a, 41% R-142B

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refrigerant (classified A1, low toxicity, no flammability). All areas of the facility are supplied with conditioned air, except the conference rooms and the hallway, which can be shut off with a variable volume vent. The ceilings are 10 feet high. The quantity of refrigerant in the packaged unit for every 1,000 cu. ft. is as follows: 20 lbs./(27,500/1,000) =.727 lbs. per 1,000 cu. ft. Table 1 allows up to 9.4 lbs. per 1,000 cu. ft. for R-22 in this type of system. This facility does not exceed that amount; therefore a separate mechanical room is not required for compliance with ASHRAE 15-1994. The limits in Table 1 can also be used to calculate the minimum volume of occupied space a refrigeration system requires. For example, the allowable 9.4 lbs. per 1,000 cu. ft. inverted (1000/9.4) determines that 106.38 cu. ft. of occupied space is required for each pound of R-22.

FIGURE 4

Mixed Occupancy Facility
Offices (3) 2,250 cu. ft. each.... 6,750 cu. ft. Reception area.......................... 6,000 cu. ft.

Manufacturing Area 20'x40' Hallway

Warehouse................................. 6,750 cu. ft Manufacturing area..................8,000 cu. ft. Total............................................27,500 cu. ft.

Warehouse 15'x45'

Office 15'x15' Office 15'x15' Office 15'x15' Conference Room 15'x15' Reception Area 20'x30'

Conference Room 15'x15'

Sizing of Relief and Rupture Devices
ASHRAE 15-1994 specifies the appropriate sizing of pressure relief devices based on a minimum required discharge capacity in pounds of air per minute. The equation is shown in Figure 5. When converting a chiller to a new refrigerant, it is critical to check the size
FIGURE 5

Purge System and Relief Devices
The standard specifies that all purge systems — including high-efficiency systems — and other relief devices must vent outside. While it may be economical to tap into existing rupture disk lines, do consider putting a drain valve in the line or wrapping the line in heater tape. Even the highest-efficiency purges lose some refrigerant. When warm gas hits a cold pipe it will condense down into the pipe, depositing refrigerant against the safety rupture disk. These disks are usually only a 0.03" thick layer of carbon and are not tolerant of corrosive conditions.

of existing safety devices to be sure they are suitable. The new standard 15-1994 also includes rating formulas for discharge capacity of rupture members and maximum length of discharge piping (Figures 6 and 7). Additional detailed information on maximum lengths for discharge piping is addressed in ASHRAE 15 addenda a, b and c. A word of caution: chillers with different refrigFIGURE 6

erants should never have common relief piping. Every refrigerant has a unique pressure rating. Using common relief valve or rupture disk piping could implode or interfere with proper operation.

Refrigerant Sensors
According to ASHRAE 15-1994, all mechanical rooms must have a sensor capable of detecting refrigerant loss. Sensors should be
FIGURE 7

Discharge Capacity of Pressure Relief Devices

C=fDL
Where: C = minimum required discharge capacity of relief device in pounds of air per minute (kg/s) D = outside diameter of vessel in feet (m) L = length of vessel in feet (m) f = factor dependent upon type of refrigerant* * identified in the standard for most refrigerants (if not, consult your equipment or refrigerant manufacturer).

Discharge Capacity of Rupture Member

C = 0.64 p1d 0.5 d = 1.25 (c/p1)
Where: C = rated discharge capacity in pounds of air per minute(kg/s) d= smallest of the internal diameter of the inlet pipe, retaining flanges, fusible plug, and rupture member in inches (mm)

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Maximum Length of Discharge Piping

L = 9 p2d5/16Cr2
Where: Cr = rated discharge capacity as stamped on the device by manufacturer in pounds of air per minute (kg/s) d = internal diameter of pipe, in inches (mm) p = length of discharge pipe in feet (m)

p = (rated pressure psig [kPa gage] x 1.10) + 14.7 (101.33)

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FIGURE 8

Examples of Sensor Locations (Examples Not in Standard)

Mechanical Ventilation to the Outdoors
Mechanical rooms must be vented to the outdoors using mechanical ventilation. The formula ASHRAE provides for calculating ventilation capacity requirements is shown in Figure 9.

Access Restrictions
The revised standard specifies that access to mechanical rooms should be restricted to authorized personnel. In addition, the room must have tight-fitting doors that open and close freely (i.e., no fire doors) and any other opening that would permit the passage of refrigerant must be sealed. Each entrance to a refrigerating machinery room must have a legible permanent sign that reads “Refrigerating Machinery Room — Authorized Personnel Only,” and should communicate that when an alarm has been activated, entry is forbidden except by trained personnel who can address emergencies.

positioned where vapor from a refrigerant leak would most likely concentrate, providing early warning so that personnel can prevent catastrophic refrigerant loss (Figure 8). Sensors should be calibrated so that the allowable exposure limit for the refrigerant will not be exceeded. Exposure limits are expressed as threshold limit value, time-weighted average (TLV-TWA). This is the time-weighted average concentration for a normal eight-hour work day and a 40-hour work week to which nearly all workers may be repeatedly exposed without adverse effects. The sensors should actuate an alarm and mechanical ventilation, as well as activate visual and audible alarms inside and outside the mechanical room. The reset for these alarms should be manual, and located inside the mechanical room. Rather than a refrigerant detector, the old version

ASHRAE 15-1992 required an oxygen deprivation sensor for class A1 refrigerants. The old standard stated that the sensor should be capable of detecting a 0.5% decrease in room oxygen levels (air is typically 20% oxygen, so the sensor would detect a drop to 19.5%). In this old scenario, 67,000 ppm refrigerant concentrations could accumulate before the sensor issued a warning! Safety stewardship and refrigerant containment are better served by using a quality refrigerant sensor with all refrigerants. A good choice is a multi-port refrigerant detector using infrared spectrometry sensing units rather than metal oxide sensing units. Infrared sensors typically hold calibration and are of higher overall quality. Facilities may find it useful to have multiple levels of alarms or to provide a refrigerant detector that indicates the actual refrigerant level (with a digital readout show-

ing refrigerant ppm). This will provide technicians with a better understanding of the refrigerant leak and the proper protection and response. The main alarm must still be a manual reset housed in the mechanical room. It is unwise to rely on automatic detectors to announce that an event is over. They do not allow technicians to distinguish between an alarm reset when the concentration dropped (e.g., because ventilation fans controlled the incident) and one that may reset because the detector was damaged. In the latter case, anyone entering the refrigerating machinery room might be entering a hazardous area. Alarms or indicators intended to communicate normal, current conditions inside the mechanical room may, of course, be automatically re-setting.

Refrigerant Storage
Section 11.5 of ASHRAE 15-1994 reads: “The total amount of refrigerant stored in a machinery room in all containers not provided with
FIGURE 9

Mechanical Ventilation

Q = 100 x G0.5
Where: Q = air flow in ft. per minute (liters per second) G = mass of refrigerant in lbs. (kgs) in the largest system, any part of which is located in the mechanical room
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relief valves and piped in accordance with the standard should not exceed 330 lbs.” This is designed to allow building owners to store adequate quantities of refrigerant for chiller servicing in separate, approved storage tanks. This is allowable under U.S. Environmental Protection Agency (EPA) guidelines, and many owners are opting to contain their CFC and HCFC chillers and safely store service refrigerant onsite. Although the ASHRAE recommendation is for a maximum of 330 lbs. per system, local building and fire codes should be checked for possible exceptions.

leak is detected. Yet another option (though not specified in ASHRAE 15) is to isolate the boiler or openflame device with a wall or separate enclosure.

Room Dimensions
The new standard defines an appropriately sized mechanical room as one that allows access to all equipment, including adequate space for service and maintenance, as well as operation.

Periodic Testing
Ventilation systems and sensors must be periodically tested in accordance with the manufacturer’s recommendation and/or local jurisdiction. This is particularly important for refrigerant sensors that are detecting compounds with low allowable exposure limits. Many of these sensors require frequent calibration.

Relief Discharge Location
The discharge location of relief devices must be at least 20 feet away from any ventilation openings, and not less than 15 feet above ground level (to avoid spraying someone with refrigerant).

Combustion Device Limitation
ASHRAE 15-1994 prohibits the location in a mechanical room of any open-flame device using combustion air from inside the room. On the other hand, an open-flame device such as a boiler may be located in a mechanical room if combustion air is drawn from outside. Two acceptable alternatives are to duct outside, sealed ventilated air in; or to install a sensor that shuts the flame off in the presence of refrigerant gas. Most refrigerant sensors are multi-port, so they can run to several spots in the mechanical room and be programmed to shut the boiler down if a chiller

Emergencies in Refrigerating Machinery Rooms
With the removal of self contained breathing apparatus (SCBA) under Addendum d of ASHRAE 15-1994, machinery rooms must have an emergency response plan. The requirement for SCBA in the previous standard was an attempt to address toxicity and concern over the risks associated with refrigerant loss. However, in most commercial buildings personnel properly trained in the use of SCBA may not be available during an emergency, or it may be difficult to locate the SCBA in an area accessible to these people. When a refrigerant detection level above the threshold limit value

(TLV-TWA) trips the alarms, personnel who are not provided with and trained to use respiratory protection equipment appropriate for the refrigerant (such as canister respirators or SCBA) must leave the room immediately. Keep in mind that alarm activation is dependent on the concentration and the toxicity of the refrigerant (programmed in the alarm settings). In a proper application of ASHRAE-15, the machinery room ventilation should actuate, reducing the refrigerant concentration, and respiratory protection may not be needed. Presence of refrigerant above the TLV-TWA limit does not by itself signal an emergency; many routine service operations can create such levels, especially with low pressure refrigerants (e.g., R-123). Local or national regulations often prescribe that steps be taken to protect the health and safety of personnel working in the machinery room when refrigerant concentrations rise above the threshold limit value. In a more sophisticated facility, with appropriate training and other measures specified by local regulations, refrigeration technicians might use this alarm as a signal to don respiratory protection. Evacuation of the machinery room may not be necessary, although warning bystanders not to enter still is. Selection of the proper respiratory protection for the particular situation may require additional information, for example, whether or not the refrigerant concentration is above the “immediately dangerous to life or health” (IDLH) level. This is defined as the maximum concentration from

which unprotected persons are able to escape within 30 minutes without escapeimpairing symptoms or irreversible health effects. It should be noted that donning respiratory protection is a last resort option under most industrial hygiene regimens — it is preferable to provide engineering controls to reduce refrigerant concentrations to tolerable levels. The refrigerant detector should activate the machinery room ventilation system, automatically reducing concentrations. In many cases, this may be entirely adequate to reduce the concentration, and respiratory protection may not be needed. An alarm silence switch is useful for situations when personnel are to remain working in the room. Figure 10 shows TLVTWA and IDLH levels for two popular refrigerants.

Example Emergency Procedure
As an example, let’s look at a facility that uses its own technicians to handle minor problems in a mechanical room. It is important to remember, however, that there are many other possibilities; and that other types of buildings, such as office, shopping centers, theaters, schools and other public assembly areas may not have their own technicians. When a refrigerant alarm sounds, personnel should leave (or not enter) the mechanical room and facilities management should be contacted immediately. A readout of the current refrigerant leak inside the machinery room via a digital reading outside the machinery room should distinguish the current reading from the alarm trip level. This refrig-

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FIGURE 10

TLV-TWA and IDLH Levels For Two Popular Refrigerants
Quantity of Refrigerant 45' x 45' x 12', Unventilated Mechanical Room @ 72° F TLV-TWA IDLH

Example Refrigerant Exposure Limits

Refrigerant

TLV-TWA

IDLH*

HCFC-123

10 – 50 ppm**

4,000 ppm

6.8 oz.

32 lb.

HFC-134a

1000 ppm

50,000 ppm

34 lb.

1,701 lb.

* Based on ARI bulletin in conjunction with refrigerant manufacturers — no formal IDLH levels have been set ** Different refrigerant manufacturers rate HCFC-123 differently: Allied at 10 ppm and Dupont at 50 ppm

erant level provides qualified refrigerant technicians or response teams with an understanding of the emergency, and appropriate respiratory protection suitable for use in an atmosphere containing refrigerant. If the proper ventilation is operating, the leak or exposure may be below the allowable expose limit. After donning appropriate respiratory protection, technicians may re-enter the machinery room to close valves, fix leaks, shut off alarms, etc. — if, and only if, the current refrigerant level is below the IDLH. In other words, technicians may re-enter the room if the refrigerant release is incidental and they have been trained in the use of protective respiratory equipment. If, for some reason, the IDHL level is exceeded or the problem seems uncontrolled and getting worse, technicians should leave and call for emergency responders. An emergency

coordination procedure with the local emergency response agency should be in place. As we have learned from past incidents, the requirements in the ASHRAE standard provide minimum protection to help prevent injury from accidents.

READ ASHRAE 15-1994
Clearly, there are many issues for professionals to consider in order to achieve compliance with ASHRAE 15-1994 and its addenda. Your best strategy is to obtain a copy of the standard and read it thoroughly, using this issue of Analysis as a point of reference. ASHRAE 15-1994 offers many good, safe solutions. Not only is it a good idea to follow the new standard, it may very well be the law in your jurisdiction — and as a professional applying ASHRAE 15, the risk is yours.

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