(NCG's)/HYDROGEN SULFIDE (H2S) - International Paper

NCG Safety & Health Manual INTERNATIONAL PAPER 

Effective: 3/9/11 Franklin, VA 

Reviewed: 3/9/11 Page 1 of 23 

NON-CONDENSIBLE REDUCED SULFUR GASES 

(NCG’s)/HYDROGEN SULFIDE (H2S) 

Executive Summary 

Employees may be at risk of non-condensible sulfur gas (NCG) exposure in kraft pulping 

operations where a mixture of sodium hydroxide and sodium sulfide (white liquor) is 

used to digest wood chips. Emissions of these gases pose the potential for exposure to 

employees working in all areas of the mill (Fibers, Chemical Recovery, Wastewater, and 

the Fluff Machine). In addition, hydrogen sulfide can also be generated when acid mixes 

with sulfide containing liquors in the process sewers or during acid cleaning operations. 

Due to the flammability of high concentrations of non-condensible gas streams, and their 

associated organic contaminants, there is additional risk of explosion which needs to be 

addressed. These sources include continuous digester relief, turpentine recovery, foul 

condensate storage, evaporator hotwells, systems where these gases are incinerated, as 

well as process sewers. 

1.0 PURPOSE 

1.1 This procedure establishes a program for reducing potential exposure to 

hazardous concentrations of non-condensible reduced sulfur gases. 

2.0 SCOPE 

2.1 This program applies to International Paper Franklin Mill and contractor 

employees. 

3.0 RESPONSIBILITIES 

3.1 Safety Manager 

3.1.1 Designated as NCG Procedure Coordinator. 

3.1.2 Maintain training materials for NCG Procedure. 

3.1.3 Maintain file of all documents associated with this procedure. 

3.1.4 Coordinate all personal and area monitoring required by this 

procedure. 

3.1.5 Lead team to perform process hazard analyses as required by this 

procedure. 

3.1.6 Perform annual audit as required by this procedure. 

3.1.7 Provide guidance to Departments on selection of fixed and 

personal monitors. 

3.1.8 Investigate all reports of employee NCG exposure. 

WARNING: Do not use this document after end of shift March 5, 2012




3.2 Medical Department 

3.2.1 Maintain personal exposure data in employee medical files for 30 

years. 

3.2.2 Inform safety manager of any medical reports of NCG exposure. 

3.3 Environmental Engineering 

3.3.1 Designate employee to serve on NCG survey team. 

3.3.2 Investigate and document all community NCG odor complaints. 

3.4 Department Management 

3.4.1 Ensure employees are trained in accordance with this procedure. 

3.4.2 Ensure equipment is maintained to reduce potential for NCG 

exposures. 

3.4.3 Maintain and update all applicable operating procedures as needed. 

3.4.4 Fibers and Power & Recovery will coordinate Management of 

Change (MOC) for NCG processes within their respective 

departments. 

3.4.5 Fibers, Power and Recovery, and Maintenance may designate 

employees to serve on the NCG survey team as needs dictate. 

3.5 Employees 

4.0 DEFINITIONS 

3.5.1 Cooperate and provide needed information for NCG survey as 

required by this procedure. 

3.5.2 Attend training as required by this procedure. 

3.5.3 Follow the provisions of applicable operating procedures. 

4.1 Non Condensible Sulfur Gases (NCGs): NCG’s are toxic, corrosive, and 

flammable by-product gases of the Kraft pulping process. They consist of 

a mixture of hydrogen sulfide, methyl mercaptan, dimethyl sulfide, 

dimethyl disulfide. NCG’s are also contaminated with organics such as 





turpentine, methanol, and acetone and therefore pose a risk of fire and 

explosion. 

4.2 Immediately Dangerous to Life and Health (IDLH): The maximum 

concentration from which one could escape within 30 minutes without a 

respirator and without experiencing any escape impairing or irreversible 

health effects. The IDLH for NCGs are listed below: 

4.2.1 Hydrogen sulfide: 100 ppm 

4.2.2 Methyl Mercaptan: 150 ppm 

4.2.3 Dimethyl Sulfide and Dimethyl Sulfide: Not Established 

4.3 Occupational Exposure Limits (OEL): The volume of contaminant in 

air/volume of total air allowed for a designated time period. Occupational 

exposure limits for hydrogen sulfide and methyl mercaptan have been 

established by OSHA and ACGIH. International Paper has established 

internal exposure limits for dimethyl sulfide and dimethyl disulfide as no 

regulatory or consensus standards have been established. The 

occupational exposure limits are as follows: 

4.3.1 Hydrogen sulfide 

4.3.1.1 OSHA Ceiling, 20 ppm 

4.3.1.2 ACGIH 8-hour Time Weighted Average, 10 ppm 

4.3.1.3 ACGIH 15 minute Short Term Exposure Limit, 15 ppm 

4.3.2 Methyl Mercaptan 

4.3.2.1 OSHA Ceiling, 10 ppm 

4.3.2.2 ACGIH 8-hour TWA, 0.5 ppm (based on odor) 

4.3.3 Dimethyl Sulfide 

4.3.3.1 ACGIH 8-hour Time Weighted Average, 10 ppm 

4.3.4 Dimethyl Disulfide 

4.3.4.1 ACGIH 8-hour Time Weighted Average, 0.5 ppm 

4.4 Management of change (MOC): are written procedures to manage and 

review all changes made to process chemicals, technology, personnel, 

equipment, and procedures (except for replacement in kind) that could 

affect the safety of the process. The responsibilities for these procedures 

rest with the affected operating departments. 





4.5 Area Monitors: Fixed, continuous, multi-sensor monitoring systems for 

hydrogen sulfide are located in designated areas. Operators in the 

appropriate control rooms will be responsible for monitoring these 

instruments. 

4.6 Personal Exposure monitoring: A method of measuring an individual’s 

exposure to a hazardous air contaminant. Personal exposures monitoring 

collects the air containment at the breathing zone of an employee, and 

therefore represents the truest measure of an employee’s exposure, during 

the timeframe in which it was collected. 

4.7 Personal Monitor: An H2S monitor worn by an individual working in an 

area which will give an alarm if air levels reach unacceptable amounts of 

H2S. 

4.8 Process Hazard analysis (PHA): A thorough, orderly, systematic approach 

or method of identifying, evaluating, and controlling the hazards of 

processes involving hazardous chemicals. 

4.9 American Conference of Governmental Industrial Hygienists (ACGIH): 

Consensus group that researches occupational health hazards and 

establishes exposure recommendations. 

4.10 Designated NCG Areas: Mill area or condition where high levels of 

NCG’s may exist under the right conditions. 

5.0 REFERENCES 

5.1 International Paper Health and Safety Program Guideline HSPG-04. 

5.2 Occupational Safety and Health Administration Regulations, 29 CFR 

1910.1000. 

5.3 American Conference of Industrial Hygienists TLVs. 

5.4 Franklin Mill’s Opening Dangerous Systems Procedure 

5.5 Franklin Mill’s Hot Work Procedure. 

5.6 Franklin Mill’s Respiratory Protection Procedure. 

5.7 Franklin Mill’s Emergency Response Procedure. 

5.8 International Paper Technology Non-Condensible Reduced Sulfur Gas 

System Design Guidelines. 





6.0 PROCEDURE 

6.1 NCG Review and Audit 

6.1.1 An analysis to identify where actual and potential NCG hazards 

exist and to assess the need for equipment repair, engineering 

controls, or administrative controls to minimize NCG hazards will 

be conducted. This analysis will be documented using the 

checklist in Appendix A. 

6.1.2 The analysis will be conducted by a team formed by members 

from various departments. Safety, Fibers, Power and Recovery, 

Environmental Engineering and Maintenance employees will be 

considered (although all are not required) for this team. 

6.1.3 The analysis will be updated when new NCG systems are installed 

and when process conditions change on existing NCG systems. 

6.1.4 The analysis will be revalidated at least every five years. 

6.2 Periodic Facility Review 

6.2.1 An annual leak detection and repair audit will be performed by 

Environmental Engineering. 

6.2.1.1 If a leak is detected, repairs must be started within five 

days and completed by 15 days. 

6.2.1.2 Deviations from the required repair schedule must be 

reported to DEQ. 

6.2.2 Operating departments must perform a visual inspection of the 

NCG generation, collection, and incineration systems on a monthly 

basis to ensure the system is properly maintained and the safety 

systems are in-place as designated. These areas include NCG gas 

and condensate systems. 

6.2.3 A review of the NCG procedure will be conducted annually by the 

site Safety Manager to ensure the requirements of the procedure 

are followed as well as to identify any necessary changes to the 

procedure. 

6.2.4 Audit reports and corrective action plans will be maintained for 

three years. 





6.3 Exposure Assessments 

6.3.1 Personal Exposure monitoring will be performed at least once 

every 5 years. 

6.3.2 Area monitoring using OSHA accepted methods will be used to 

perform an initial assessment. 

6.3.3 In addition, personal exposure monitoring using OSHA accepted 

methods will be performed when initial assessment shows 

exposures at or near the occupational exposure limit. 

6.4 Dispersion Modeling 

6.4.1 Dispersion modeling of potential NCG release points may be 

conducted and documented. 

6.4.2 Dispersion modeling data may be updated whenever new systems 

or process changes are implemented that affect potential NCG 

releases. 

6.5 Control of Exposure 

6.5.1 Engineering Controls 

6.5.1.1 Engineering controls will be the primary means of 

controlling NCG hazards and exposures. 

6.5.1.2 Basic types of engineering controls are listed below: 

6.5.1.2.1 Diking acid tanks/container storage. 

6.5.1.2.2 Separating acid and sulfide sewers. 

6.5.1.2.3 Process changes (e.g., neutralization of 

chlorine dioxide salt cake and sewered acid) 

6.5.1.2.4 NCG collection and incineration. 

6.5.1.2.5 Venting sludge press and belt filters. 

6.5.1.2.6 Adjusting NCG vent heights based on 

dispersion modeling of NCG releases. 

6.5.1.3 All new or upgraded NCG systems should conform to the 

latest version of the International Paper Technology Non- 

Condensable Reduced Sulfur Gas System Design 

Guidelines. 





6.5.1.4 A Process Hazard analysis (PHA) of all new or modified 

NCG collection and incineration systems will be 

performed. In addition, a PHA will be completed when 

process conditions change that could significantly affect 

NCG hazards/exposures. 

6.5.1.5 PHA’s will be revalidated every 5 years. 

6.5.1.6 Persons knowledgeable in the process and in PHA 

methods and techniques will conduct the PHA. 

6.5.1.7 Changes to the NCG system will be tracked through a 

formal Management of Change (MOC) process. 

6.5.2 Administrative Controls 

6.5.2.1 Administrative Controls will be used as the secondary 

means of control. 

6.5.2.2 Operating procedures will be established for the 

following: 

6.5.2.2.1 Acid cleaning digesters, liquor heaters, 

evaporators, recovery boiler, green liquor lines 

and mud filters (or any process where sulfidecontaining 

liquids are mixed with acids). 

(Note: there are very specific requirements for 

acid cleaning procedures. 

6.5.2.2.2 Response to NCG vents to the atmosphere. 

6.5.2.2.3 NCG line breaking as listed in the Franklin 

Mill’s Opening Dangerous Systems Procedure. 

6.5.2.2.4 Loading/unloading black liquor soap, brine, 

sodium hydrosulfide and turpentine. (Note: 

there are very specific requirements for 

turpentine) 

6.5.2.2.5 pH adjustment in process sewer. 

6.5.2.2.6 Handling/processing wastewater treatment 

sludge. 

6.5.2.2.7 Using and responding to personal and area 

monitors. 

6.5.2.2.8 Hot work on NCG system as outlined in the 

Franklin Mill Hot Work Procedure. 

6.5.2.2.9 Cleaning any tank containing fiber residue 

(decaying stock is also a source of NCG gas 

release). 





6.5.2.3 Area monitors will be placed in areas with high potential 

for NCG release. Monitors must be calibrated (with 

calibration gas) and maintained per manufacturer’s 

instruction (minimum monthly requirement). Alarms will 

be set based on most protective OEL (e.g. 8 – hour TWA). 

6.5.2.4 Personal monitors will be worn by employees working in 

areas where fixed monitors are inoperable. One monitor is 

adequate for more than one individual as long as they 

remain in reasonably close proximity to each other. 

Employees should check to make sure personal meter is 

functioning properly in clean atmosphere prior to entering 

NCG area. Personal monitors will be calibrated monthly 

(minimum) with calibration gas. Calibration will be 

performed according to the manufacturer’s guidelines. 

6.5.3 Personal Protective Equipment 

6.5.3.1 Personal Protective Equipment (PPE) will be used as a 

tertiary means of control. 

6.5.3.2 All employees working in TRS designated areas will have 

an escape respirator in their possession. 

6.6 Designated NCG Designated Areas 

6.6.1 General Requirements for Working in Area 

6.6.1.1 Entrances to the NCG designated areas may be marked by 

caution signs. These signs will state "Caution - Designated 

TRS area - check in at appropriate control room before 

working in the area. An escape respirator must be in your 

possession.” 

6.6.1.2 NCG Designated Ares include: 

(1) Around any NCG rupture disk or atmospheric vent. 

(2) E set hotwell. 

(3) Any NCG equipment where maintenance or 

troubleshooting is being performed. 

(4) Turpentine decanter and storage tank dike 

(5) Turpentine Storage and Loading Facility 

(6) Acid and process sewer mixing (pH control station) 

(7) LK burner Deck 

(8) RTO 

(9) Sludge building and clarifiers 

(10) Landfill leachate area 





6.6.1.3 Employees who are not assigned daily to the area must 

check in with the appropriate control room. Ask about any 

TRS concentrations in the area and inform the control room 

operators regarding the location and duration of the job 

task. 

6.6.1.4 When the fixed, continuous monitor sensors and/or the 

sensor audio/visual alarms are inoperable or unreliable, 

employees entering the area will be required to use a 

personal hydrogen sulfide monitor. One monitor is 

adequate for more than one individual as long as they 

remain in reasonably close proximity to each other. These 

monitors must be approved for use by the Safety 

Department and properly calibrated. 

6.6.1.5 Employees must have in their possession a minimum of a 

North 7902 organic vapor/acid gas escape respirator. 

6.6.1.6 Employees entering and working in the designated area are 

responsible for informing control room operators and/or 

their supervisor of any unusual concentrations of TRS 

gases noted while in the area. These employees will 

evacuate the TRS area if TRS concentrations are known or 

suspected to be hazardous, and whenever the audio/visual 

alarms are activated. 

6.6.1.7 Upon knowledge of a condition or process upset which has 

or might potentially result in the emission of hazardous 

concentrations of TRS gas, the control room operator will 

initiate notification of those individuals in the TRS area 

who might be exposed to these concentrations. Log book 

entries will be made accordingly. 

6.7 Respiratory Protective Equipment 

6.7.1 Respiratory protection will be used in accordance with the Franklin 

Mill’s Respiratory Protection Procedure. 

6.7.2 Only supplied air respirators may be used to work in known or 

unknown concentrations of NCG. 

6.7.3 Air purifying respirators, such as the North 7902 escape respirator, 

are approved for escape only. 





6.8 Emergency Procedures 

6.8.1 Emergency Procedures are outlined in the Franklin Mill’s 

Emergency Response Plan. 

6.9 Notification of Exposure 

7.0 TRAINING 

6.9.1 Employees who experience adverse health effects from exposure to 

NCG must report to Medical as required in the Franklin Mill’s 

Incident and Injury Reporting Procedure. 

6.9.2 Medical will notify the Safety Manager of all reported NCG 

exposures. 

6.9.3 The Safety Manager will report any significant (explosion, 

hospitalization, etc.), unusual or unexpected sources of exposure 

per Corporate requirement. 

6.9.4 The Safety Manager will investigate all reported NCG exposures 

and will perform monitoring as necessary to assess exposure. 

7.1 All employees working in or around NCG hazards will be trained before 

assignment and annually on the NCG Procedure. 

7.2 Training will include the following: 

7.2.1 Recognition of NCG hazards. 

7.2.2 Applicable operating procedures. 

7.2.3 Health hazards of NCG’s. 

7.2.4 Fire/Explosion hazards of NCG’s. 

7.2.5 Appropriate emergency and evacuation procedures. 

7.2.6 Summary of any monitoring conducted in applicable area. 

7.2.7 Use of personal monitoring equipment. 

7.2.8 Use of emergency respiratory equipment. 

8.0 DOCUMENTATION 

8.1 The NCG Survey (Appendix A) will be updated at least every five years 

and when process changes occur. The NCG Survey will be retained until 

superceded. 

8.2 Documentation related to the annual audits of the NCG procedure will be 

retained for three years. 





8.3 Employee training records will be retained until superseded. 

8.4 Calibration and maintenance data for area monitors will be retained for 

three years (via the work order system). 

8.5 Calibration and maintenance data for personal monitors will be retained 

for three years (currently at S:\Data\Projects\Mill Closure\Safety Notes 

and Inspections\ biosystems calibration log “Year” .xlsx). 

8.6 PHA documentation will be kept for the life of the process. 

8.7 Applicable NCG operating instructions will be retained until superceded. 

8.8 Personal exposure monitoring data will be retained in the affected 

employee’s Medical file for at least 30 years. 

8.9 Area monitoring data will be retained in the Industrial Hygiene files for 30 

years. 

9.0 APPROVAL AND ISSUE 

This procedure is approved by the Franklin Lead Team. 

10.0 REVISION HISTORY 

DATE MODIFICATIONS 

Mar 1, 2011 New 





ATTACHMENT A 

NCG/H2S SURVEY CHECKLIST 





I. SEWERS AND WASTEWATER TREATMENT 

A. P & ID Review 

___ Identify location of sample points where NCGs are likely to evolve (e.g. parshall 

flumes and foam boxes). 

___ If possible, obtain sample results for pH and flows at each sample point for the 

past 30 days (e.g., pH levels less than 9.5 found in sewers which contain sulfides 

(such as spent liquors) have the potential to generate H2S gas). 

___ Identify locations where sulfides and acids may mix in sewers or clarifiers. 

___ Determine if any vents are installed on closed sewers. If vents are installed, 

determine vent height from ground and concentration and flow of NCGs from 

ent. 

___ Determine if acid and sulfide sewers mix at waste treatment. 

___ Determine where acid is added for pH control. 

B. Interview Lab Sample Takers and Wastewater Treatment Operators 

___ Question sample taker and wastewater treatment operators on potential NCG 

areas. 

___ Question sample taker on any swings in pH of sewers. 

C. Survey Sewers 

___ Note location and condition of area monitors that are positioned to monitor 

sewers. 

___ Monitor in areas where sulfide and acid sewers combine. 

___ Monitor open foam boxes and parshall flumes. 

___ Monitor sewer vents, if reachable. 

___ Determine height of sewer vents relative to surrounding work areas. 

D. Survey Wastewater Treatment 

___ Monitor where sewer exits closed sewer and enters waste treatment. 





___ Monitor where sewer streams combine before clarifying (if applicable). 

___ Monitor at splitter box (if applicable). 

___ Determine if the acid storage tank used for pH adjustment is diked to contain the 

contents of the tank or routed to a non-sulfide source. 

___ Monitor while acid is added for pH control. 

___ Monitor top or vent of sludge mix tank (if reachable). 

___ Monitor sludge presses and other sludge processing equipment. 

___ Monitor effluent of sludge processing equipment. 

___ Determine if leachate is collected from the landfill. Request to be taken to the 

collection location to monitor (if applicable). 

II. NCG SYSTEM AND THE LIME KILN 


1. NCGS 

___ Identify all NCG sources for each type of stream. 

___ Identify the location of all rupture disks. 

___ Identify all NCG vents. 

___ Determine vent height, NCG concentration, and flow. 

___ Identify the location of all NCG eductors. 

___ Inquire if any modifications have made to the original installation. 

___ Determine NCG scrubbing media, if applicable. 

___ Determine disposal of NCG scrubbing media. 

___ Identify primary and alternate NCG disposal systems (i.e., incinerator, 

lime kiln, boiler, atmospheric vent). 





___ Determine routing of condensate to sewer. 

___ Identify location of NCG seal pots for condensate. 

___ Identify location of flame arrestors. 

2. Recausticizing 

B. Survey NCGs 

___ Locate acid storage in area for mud filter washing. 

___ Note location and condition of area monitors (e.g., H2S monitors) positioned to 

monitor the NCGS. 

___ Locate all rupture disks and evaluate locations. 

___ Locate all NCG vents and evaluate locations and heights relative to surrounding 

work areas. 

___ Locate flame arrestors and assure each has blank flanges or valving so line can 

be isolated while performing maintenance on flame arrestor. 

___ Assure each flame arrestor has taps on each side for pressure measurement to 

test for pluggage. 

C. Interview Lime Kiln Operator 

___ Question the operator on potential NCG areas. 

___ Determine how an operator knows when a rupture disk is blown. 

___ Question the operator on the response that is made when a disk is blown. 

___ Determine how often a rupture disk is blown. 

___ Determine how often NCG is vented at the kiln and at the source. 

___ Determine if green liquor lines are acid cleaned. What precautions are taken? 

___ Question the operator about H2S coming off the vent of the sodium hydrosulfide 

(NaHS) (or NaSH) storage tank while filling. Determine what precautions are 

taken while filling. 





___ Question operator about H2S exposure during mud filter acid cleaning. 

___ Question the operator on location of area monitors in limekiln area (if 

applicable). 

D. Survey Lime Kiln 

III. PULP MILL 

___ Note location and condition of area H2S monitor (if applicable). 

___ Locate acid storage and determine potential of acid leak combining with a 

sulfide source (i.e. diked tanks, remote drum storage). 

___ Determine if unlabeled acid lines are routed over sulfide sources. 

___ Inspect acid truck unloading pad to assure leaks will not combine with sulfide 

sources (if applicable). 

___ Locate and monitor where spent white liquor NCG scrubbing liquid is injected 

into recausticizing system (if applicable). 


___ Determine source of wash water (i.e. combined condensate, stripped condensate, 

contaminated hot water). 

___ Determine if the chip bin on a continuous digester(s) has a pressure/vacuum 

relief. 

___ Determine if digester flash steam condensate is sewered or used in process. 

___ Identify acid storage/day/cleaning tanks. 

___ Review ClO2 generation to determine route of spent acid (if R-2 or R-8) and 

dissolving of salt cake (i.e. acidic salt cake dissolved in black liquor). 

___ Review turpentine system loading/unloading procedures (if applicable). 

___ Ask for a copy of the written acid cleaning procedures. 

___ Determine if the mill has installed a system to dissolve ClO2 generator salt cake 

in water before mixing with black liquor (if applicable). 





___ Determine if white liquor is used as scrubbing media for the bleach plant 

scrubber and the disposal location for the media. 

B. Interview Pulp Mill Operator 

___ Question the operator on potential NCG areas. 

___ Determine how an operator knows when a NCG rupture disk is blown. 

___ Question the operator on the response that is taken when a disk is blown. 


___ Determine how often NCG vent at the source. 

___ Question the operator on what the pulp mill cleans with acid. 

___ Determine if the acid from acid cleaning is neutralized before sewering. 

___ Question the operator on location of area monitors in pulp mill area (if 

applicable). 

C. Survey Pulp Mill 

___ Determine purpose of all vent stacks and note height. 

___ Note location and condition of area H2S monitors, if applicable. 

Note: Evaporators are covered in the power plant section. 

1. Continuous Digesting 

___ Determine the source of air for the control room. 

___ Monitor top of the chip bin and around the boot. 

___ Monitor around knot conveyor if it enters the chip bin. 

___ Monitor the steaming vessel. 

___ Determine if flash steam condensate goes to a closed or open sewer. 





2. Turpentine System 

___ Determine if gases from the turpentine decanter under-flow are vented 

and assess the location of the vents. 

___ Determine how the underflow is transferred from the decanter. If 

transferred to a tank, assure the tank is sealed. If piped to a sewer, 

assure the sewer is closed and/or sealed. 

___ Locate turpentine condenser and evaluate exposure potential to NCG. 

___ Evaluate the turpentine loading system. Is the loading process 

monitored using an automatic level detection system or is the level 

visually determined. If visually determined, is respiratory protection 

(e.g., air-supplied respirator such as an SCBA) used when operator 

takes a visual reading? Ensure Procedure 5.3 – Turpentine Loading 

and NCG/H2S is being followed. 

___ Monitor the loading process. Is the IP Loading/unloading procedure 

and form used by the operator? The Bulk Chemical loading /unloading 

forms (Truck and Rail) can be found located at: 

http://ipweb.ipaper.com/usdistribution/Rail/HBC.htm 

3. Pulp Washing 

___ Locate the contaminated hot water/stripped condensate tank and 

determine if the overflow is routed to a closed or surface sewer or if it 

is used in washing. 

___ Determine if the conductivity of the wash water is monitored to detect 

evaporator pull-over or inadequate stripping. 

___ Locate the vent to the contaminated hot water, stripped condensate, and 

stripper feed tank and evaluate exposure potential. 

___ Monitor brown stock washers if contaminated hot water/stripped 

condensate is used to wash brown stock. 

___ Locate the vent to the brown stock washers and evaluate exposure 

potential. 

4. Acid Cleaning 

___ Determine if the acid storage tanks for acid cleaning of equipment (i.e., 

liquor heaters) is diked to contain contents or routed to an acid sewer. 

Locate truck/rail car charging valve to acid storage and assess the 

potential of acid mixing with a sulfide source. 





___ Assure acid cleaning tank is diked to contain contents. 

___ Assure acid cleaning tank is vented outside of any work area and that 

tank is sealed during cleaning. 

5. Chlorine Dioxide (CIO2) Generation 

In an R-2 process, spent acid is a byproduct. In an SVP/R-3 and R-8 process 

acid is recycled in the generator. In all three processes (R-2, SVP/R3, and R-8) 

salt cake is a byproduct. The salt cake is usually slurried in water and 

neutralized before mixing with weak liquor or strong black liquor. Spent 

acid/salt cake from a chlorine dioxide generator should not be mixed directly 

with strong black liquor. 

___ Determine type of ClO2 generating process (R-2, SVP/R-3, R-8). 

___ Determine if the acid storage for the ClO2 generator is diked to contain 

contents or routed to an acid sewer if in a sulfide area. Locate truck/rail 

car charging valve to acid storage and assess the potential of acid 

leaking and mixing with a sulfide source. 

___ Determine where spent acid from the ClO2 generator is routed (if 

applicable). 

___ Trace spent acid line and identify all drain valves that would drain to 

sulfide source (if applicable). 

___ Assure spent acid line is labeled (if applicable). 

___ Assure spent acid tank is diked to contain contents or routed to an acid 

sewer (if applicable). 

___ Determine if the spent acid tank overflow is routed to a closed acid 

sewer (if applicable). 

___ Determine if the exhaust on the salt cake filter is pulling a negative 

pressure (if salt cake is mixed with liquor). 

___ Determine if the salt cake slurry tank/mix tank/dissolving tank is 

vented from a work area if salt cake is dissolved directly in black 

liquor. 

___ Determine if the salt cake slurry tank/mix tank/dissolving tank is diked 

to contain contents or routed to an acid sewer if the tank contains black 

liquor. 





IV. POWER & RECOVERY 


___ Determine the route of the overflow for the salt cake slurry tank/mix 

tank/dissolving tank. 

1. Evaporators 

2. Stripper 

___ Identify vents. 

___ Determine if evaporators are acid cleaned. 

___ Review black liquor soap storage/handling procedures. 

___ Determine condensate flows. 

___ Identify vents. 

B. Interview Evaporator Operator 

___ Question the operator on potential H2S areas. 

___ Determine how an operator knows when a rupture disk is blown. 

___ Question the operator on the response when a disk is blown. 


___ Determine how often NCGs vent and at what location. 

___ Question the operator on location of area monitors in evaporator area (if 

applicable). 

C. Survey Evaporator Area 

___ Determine purpose of all vent stacks and note height. 

___ Note location and condition of area H2S monitors, if applicable. 





___ Assure legible NCG (or H2S) warning signs are posted in potential NCG (or 

H2S) areas. 

1. Evaporators 

___ Monitor for leaks around the evaporator hotwells/seal tanks. 

___ Assure the hotwell/seal tank overflow goes to a closed sewer. If not, 

assure an area monitor is in place and that the water trap on the 

overflow is rated at a higher pressure than the NCG rupture disk. 

___ Determine if the hotwell/seal tank NCG by-pass vent to atmosphere is 

located away from a work area. 

___ Assure hotwells/seal tanks are vented to the NCG system. 

___ Check manhole covers to hotwell (if applicable) to assure they are 

bolted, sealed or locked. 

___ Determine if the contaminated/foul condensate lines and tanks are 

routed to a closed sewer. Monitor around the tank(s). 

2. Condensate Stripper (if applicable) 

___ Monitor for leaks around the condensate feed tank, stripper and vent. 

3. Weir Box/Blend Tank/Mix Tank 

4. Boiler 

This list is applicable only if spent acid (usually from CIO2 generator) is added 

to the weir box, blend tank or salt cake mix tank. 

___ Monitor around the tank. 

___ Assure the tank is vented to the NCGs. 

___ Assure the NCGs bypass vent to the atmosphere is located away from a 

work area. 

___ Review acid cleaning procedures for boilers. 





V. PAPER MACHINE 

A. Interview Operator 

___ Question the operators on potential NCG areas (i.e., NCGs from sewers). 

B. Survey Paper Machine 

___ If potential areas are identified by operators. 

VI. WOODYARD/WOOD ROOM 

A. Interview Operator 

___ Question the operators on potential NCG areas (i.e., NCG from sewers). 

B. Survey Woodyard 

___ If potential areas are identified by operators. 





NCG SURVEY DATA COLLECTION FORM 

Site Location: _______________________ Department/Area: _______________________ 

Monitoring Equipment: (Mfg.) _______________ (Model) ____________ (Serial #) ___________ 

Monitor Calibration Date: ______________ Monitoring Performed by: ____________________ 

Date/Time Sample Location Observations 

NCG Level 

(as H2S)* ppm/mg/m 3 

Note: When recording field observations, remember you are looking for potential as well as actual hazards. 

Therefore, record information on the potential for acid and sulfide sources to mix, location of NCG vents, 

frequency and type of employee work activities in areas. For potential hazard observations, mark the NCG 

level (e.g., as H2S and/or methyl mercaptan) column as “NA”.

(NCG's)/HYDROGEN SULFIDE (H2S) - International Paper

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