Operating above the solution’s Flash Point – Safety Engineering (SAFTENG)

I have written several articles on the topic of when we store our flammable liquids BELOW their flash points with the aid of refrigeration and how that makes our “refrigeration/chiller” a critical utility if we wish to take credit for storing the flammable below its FP. I have also discussed processing a Class IIIB/Cat 4 flammable liquid within 30 degrees of its FP. However, this article is about a “utility process” used for heating a process, and the heat transfer fluid (HTF) is heated above its FP.

This process and analyzing its hazards can be tricky. When we look at the Safety Data Sheets and the Technical Datasheets, these fluids are almost always listed as “Non-Flammable” as their FPs are well over 200F. So at standard temperature and pressure (i.e., 68°F and 14.7 psi), the solution is indeed NOT flammable; however, we will be heating the solution to above its FP. This is a recognized hazard by OSHA, Insurance Providers, and NFPA; which insurance and NFPA 30 provide the user(s) some excellent DESIGN features to help PREVENT a LOPC event and PROTECTION and MITIGATION layers when the LOPC event occurs.

First and foremost, codes and standards manage these hazards by setting a tolerance against operating up to 30 degrees within the solutions FP.

OSHA

1910.106(a)(19)(iii) … When a Category 3 liquid with a flashpoint at or above 100 °F (37.8 °C) is heated for use to within 30 °F (16.7 °C) of its flashpoint, it shall be handled in accordance with the requirements for a Category 3 liquid with a flashpoint below 100 °F (37.8 °C).

1910.106(a)(19)(iv) … When a Category 4 flammable liquid is heated for use to within 30 °F (16.7 °C) of its flashpoint, it shall be handled in accordance with the requirements for a Category 3 liquid with a flashpoint at or above 100 °F (37.8 °C).

1910.106(a)(19)(v) When liquid with a flashpoint greater than 199.4 °F (93 °C) is heated for use to within 30 °F (16.7 °C) of its flashpoint, it shall be handled in accordance with the requirements for a Category 4 flammable liquid.

IFC

Chapter 57 – Flammable Liquids

5701.5 Material classification.

Flammable and combustible liquids shall be classified in accordance with the definitions in rule 1301:7-7-02 of the Administrative Code.

When mixed with lower flash-point liquids, Class II or III liquids are capable of assuming the characteristics of the lower flash-point liquids. Under such conditions, the appropriate provisions of this rule for the actual flash point of the mixed liquid shall apply.

When heated above their flash points, Class II and III liquids assume the characteristics of Class I liquids. Under such conditions, the appropriate provisions of this rule for flammable liquids shall apply.

NFPA

NFPA 30, Chapter 6 Fire and Explosion Prevention and Risk Control

6.4.1.2* Storage, processing, handling, and use of Class II and Class III liquids heated at or above their flash point shall follow the requirements for Class I liquids, unless an engineering evaluation conducted in accordance with Chapter 6 justifies following the requirements for some other liquid class.

A.6.4.1.2 Storage, processing, handling, and use of Class II and Class III liquids at temperatures above the flash point can produce ignitable vapors if the liquid is released or vessels are vented. Class I liquid requirements address such events to minimize the likelihood of ignition and the consequences if ignition occurs, thus becoming a benchmark for design features when Class II and III liquids are handled above the flash point.

However, their characteristics differ from those of Class I liquids. For example, the extent of travel of the Class II and III vapors is limited by the quick condensation of released vapors as they cool to lower temperatures. This might justify a more limited electrical area classification, different ventilation, elimination of explosion venting, and so forth. In addition, the process handling these Class II and III heated liquids may incorporate safety design features that accomplish the intent of NFPA 30, that is to address the hazards of released vapors.

Further, the more restrictive building construction requirements in Table 17.6.1 might not be necessary for a particular process involving Class II, and III liquids heated above the flash point. The option of conducting an engineering evaluation in accordance with Chapter 6 was included to allow the use of alternative designs to address the level of hazards identified.

NFPA 30, Chapter 19 Specific Operations

19.4.1.1 This section shall apply only to recirculating heat transfer systems that use a heat transfer fluid that is heated up to or above its flash point under normal operation.

19.4 Recirculating Heat Transfer Systems

19.4.1 Scope

19.4.1.1 This section shall apply only to recirculating heat transfer systems that use a heat transfer fluid that is heated up to or above its flash point under normal operation.

19.4.1.2 This section shall not apply to process streams used as a means of heat transfer or to any heat transfer system of 60 gal (230 L) capacity or less.

19.4.2* General Requirements

A heater or vaporizer for heat transfer fluid that is located inside a building shall meet all applicable requirements of Chapter 17 (Processing Facilities).

Special Note:

17.3.6 Processing and handling of Class II and Class III liquids heated at or above their flash point shall follow the requirements for Class I liquids unless an engineering evaluation conducted in accordance with Chapter 6 justifies following the requirements for some other liquid class. (See 6.4.1.2 and A.6.4.1.2.)

17.3.7 When a process heats a liquid to a temperature at or above its flashpoint, the following shall apply:

(1) The process vessel shall be closed to the room in which it is located and vented to the outside of the building.

(2) If the vessel needs to be opened to add ingredients, the room ventilation shall meet the requirements of Section 17.11 and the process heating controls will be interlocked with the ventilation such that the process heat will shut down if the ventilation fails or is turned off.

(3) The process vessel shall be equipped with an excess temperature control set to limit excessive heating of the liquid and the subsequent release of vapors.

(4) If a heat transfer medium is used to heat the liquid and the heat transfer fluid can heat the liquid to its boiling point on failure of the process and excess temperature heat controls, a redundant excess temperature control shall be provided.

19.4.3 System Design

19.4.3.1 Drainage shall be provided at strategic low points in the heat transfer system. Drains shall be piped to a safe location that is capable of accommodating the total capacity of the system or the capacity of that part of the system that is isolated.

19.4.3.2 Where the heat transfer system expansion tank is located above floor level and has a capacity of more than 250 gal (950 L), it shall be provided with a low-point drain line that can allow the expansion tank to drain to a drain tank on a lower level. The drain line valve shall be operable from a safe location.

19.4.3.3 A heat transfer fluid system shall not be used to provide direct building heat.

19.4.3.4 All pressure-relief device outlets shall be piped to a safe location.

19.4.4* Fuel Burner Controls and Interlocks

Oil- or gas-fired heaters or vaporizers shall be designed and installed in accordance with the applicable requirements of NFPA 31 or NFPA 85, whichever is applicable.

19.4.5 Piping

19.4.5.1* Piping shall meet all applicable requirements of Chapter 27 (Piping Systems).

19.4.5.2 All pipe connections shall be welded.

19.4.5.2.1 Welded, threaded connections shall be permitted to be used for piping 2 in. (50 mm) and smaller.

19.4.5.2.2 Mechanical joints shall be permitted to be used at pump, valve, and equipment connections.

19.4.5.3 New piping that is to be insulated with permanent insulation and existing piping that has been disturbed and is to be reinsulated with permanent insulation shall be covered with a closed-cell, nonabsorbent insulation material.

19.4.5.3.1 Where all pipe joints are welded and where there are no other points in the system subject to leakage, such as at valves or pumps, other types of insulation shall be permitted.

19.4.5.3.2 Where dams are formed around possible leak producing areas, using metal “donut” flanges that are welded to the pipe or using a “donut” segment of nonabsorbent insulation sealed to the pipe to prevent migration of leakage into adjacent insulation, the piping from dam to dam shall be considered to be a closed system and other types of insulation shall be permitted. The area subject to leakage where the dam has been constructed shall be insulated with nonabsorbent insulation or a nonabsorbent insulation system.

19.4.5.3.3 Where removable, reusable insulated covers are required for access, the covers shall be fabricated of flexible or rigid insulation that is encapsulated in a manner to provide a nonabsorbent insulation system to prevent absorption of leakage into the insulation.

19.4.6 Fire Protection

19.4.6.1* Automatic sprinkler protection meeting the requirements of NFPA 13 for Extra Hazard (Group I) Occupancies shall be provided for building areas containing a heat transfer system heater or vaporizer.

19.4.6.2 An alternate fire protection system shall be permitted to be used, if approved by the authority having jurisdiction. Such alternate system shall be designed and installed in accordance with the appropriate NFPA standard and with manufacturer’s recommendations for the system selected.

19.4.7 Operation

19.4.7.1* Operations involving heat transfer fluid systems and equipment shall be reviewed to ensure that the fire and explosion hazards resulting from loss of containment of the fluid or failure of the system are provided with corresponding fire prevention and emergency action plans.

19.4.7.2 Operators of heat transfer systems shall be trained in the hazards of improper operation of the system and leakage and shall be trained to recognize upset conditions that can lead to dangerous situations.

19.4.7.3 Safety interlocks shall be inspected, calibrated, and tested annually or at other intervals established in accordance with other applicable standards to determine that they are in proper operating condition.

Sources:

FM Global Data Sheet 7-99, HEAT TRANSFER FLUID SYSTEMS

NFPA 30

Fire Code

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