U.S. Department of Labor t www.osha.gov t (800) 321-OSHA (6742)

Fact Sheet

Shipyard

Employment

Guidelines for Safely Entering and 

Cleaning Vessel Sewage Tanks 

Sewage systems on vessels are known as Marine Sanitation Devices (MSDs) or Collection, Holding and 

Transfer Tanks (CHTs). Cleaning these systems is required for operations such as routine surveys and 

inspections, surface preservation, equipment modification, repairs and maintenance. Entering and cleaning 

sewage tanks, piping and components present specific hazards to workers that put them at risk for injuries 

and illnesses if they are not properly protected (29 CFR 1915.13).

Workers are often exposed to dangerous atmospheres during 

tank opening and venting; manual pumping and stripping; 

breaking or dismantling components and piping; and pressure 

washing, mucking, and scaling (29 CFR 1915.11(b); 1915.12). A 

dangerous atmosphere may expose workers to the risk of death, 

incapacitation, injury, chronic or acute illness, or impaired ability 

to escape unaided from a confined or enclosed space (29 CFR 

1915.11(b)). When working on CHTs/MSDs, special attention 

should be given to good hygiene practices, proper use of personal 

protective equipment and safe confined space entry procedures 

(29 CFR 1915.88; 1915 Subparts B & I).

The information in this document can help prevent exposing 

workers to the known and unknown dangers of handling treated or 

untreated sewage and gray water tanks during tank opening, entry, 

cleaning and related operations. Related components/operations 

include: piping, aeration, vacuuming, settling, and treatment tanks 

and apparatus; sewage-contaminated water tanks or waste oil 

tanks, bilges, or sumps; and valves, pumps, grinders, macerators 

and other contaminated equipment.

Sewage and Gray Water

• Sewage or “black water” includes any wastes contaminated 

by human excrement and other effluent (liquid waste), such as 

from urinals and toilets.

• “Gray water” includes wastewaters uncontaminated by 

human excrement such as liquids from drains, sinks, sculleries, 

drinking fountains, showers, washing water, food wastes, 

laundry waste, etc. 

Common Hazards in Tanks

• Atmospheric hazards include oxygen-deficiency and 

flammable or toxic gases such as methane and hydrogen 

sulfide. Methane gas is colorless, odorless and tasteless, but 

is highly flammable and is considered an asphyxiant. Hydrogen 

sulfide (H2

S) is also colorless and flammable, but it is highly 

odorous and extremely toxic to humans. At approximately 

100–150 ppm of H2

S, the olfactory nerve is paralyzed after 

a few breaths. Within a very short time, the sense of smell 

disappears, giving a false sense that the harmful gas has gone 

away. These gases are detectable only by properly calibrated 

instruments (29 CFR 1915.12).

• Biological hazards include pathogens (e.g., bacteria, 

viruses, protozoa, parasitic worms, fungi) and other infectious 

microorganisms that can cause illnesses such as hepatitis, 

typhoid fever, dysentery and cholera. Inhaling or ingesting 

contaminated mists may result in serious illnesses.

• Physical hazards include slips, trips, and falls due to slippery 

and sloping surfaces; limited access and egress; corroded 

ladder rungs; and obstructions by piping and other structures. 

There is also the risk of receiving punctures and cuts from 

sharp edges (29 CFR 1915.81).

• Mechanical hazards include energized equipment; rotating 

machinery; and waste stream leaks. Before any servicing is 

performed where the energization or startup, or the release 

of hazardous energy may occur, all energy sources must be 

identified and isolated, and the machinery, equipment, or 

system rendered inoperative (29 CFR 1915.89(c)(1)).
• Chemical hazards include sewage treatment agents containing

ammonium compounds, formaldehyde, chlorine products, sodium

hydroxide, odor-control and sewage-biodegrading enzymes,

sanitizers, biocides, cleaning or bleaching agents, pharmaceutical

drugs, hormones and heavy metals.

Note: Other hazards may include inadequate ventilation, 

poor visibility, and heat stress.

Personal Protective Equipment (PPE) & Other 

Recommended Safe Practices

• Although Level A or B protective gear is not required, to avoid

liquid contact with exposed skin, it is recommended that full-body,

impervious suits are worn in addition to using rubber boots,

gloves, hard hats and eye protection (29 CFR 1915 Subpart I).

• Respirator selection is based

on an evaluation of respiratory

hazards in the workplace and

other relevant workplace and

user factors (29 CFR 1915.154;

1910.134(d)); however, during

entry and cleaning inside a large

sewage tank, it is recommended

that workers wear full-face,

supplied-air respirators with an

escape pack.

• During cleaning operations

performed outside a tank,

where the atmosphere is not

Immediately Dangerous to

Life or Health (IDLH), wear

supplied-air or air-purifying

respirator with organic

vapor HEPA (High-Efficiency

Particulate Arresting cartridge)

(29 CFR 1910.134(d)(3)(iv)(B)).

• Have extra flashlights and two-way radios readied for

communication.

• Have a first-aid kit, an eyewash and flushing station, neutralizing

solutions, cleaning equipment, and emergency medical services

readily available (29 CFR 1915.87; 1915.88).

Note: Respirator shown here is 

not equipped with organic vapor 

HEPA cartridge as recommended.

A worker with protective gear.

Note: For more information, see CPL 02-01-049, 29 CFR Part 

1915, Subpart I, Enforcement Guidance for Personal Protective 

Equipment (PPE) in Shipyard Employment, November 4, 2010. 

Immunization

• Ensure routine vaccinations such as for influenza and tetanus

are current. Consult your physician about the need for Hepatitis

A vaccination (NIOSH/CDC).

Training

Workers must be trained to recognize potential hazards, use proper 

work practices and procedures, recognize adverse health effects, 

understand the physical signs and reactions related to exposures, 

and are familiar with appropriate emergency evacuation procedures. 

They must also be trained to select and use the appropriate 

Personal Protective Equipment (PPE) (29 CFR 1915.12(d)(2) - (d)(3)); 

1915.1200). Training may also be required in the following areas:

• Confined Space Entry Procedures;

• Atmospheric Testing;

• Calibration of Gas Detectors;

• Respirator Selection and Fit Testing;

• Ventilation and Engineering Controls;

• HAZMAT or HAZWOPER

Atmospheric Testing Requirements for 

Confined Space Entry & Hot Work

Tank entry must not be permitted if atmospheric conditions are 

found to be Immediately Dangerous to Life or Health (IDLH). IDLH 

means an atmosphere that poses an immediate threat to life or 

is likely to result in acute or immediate severe 

health effects (29 CFR 1915.11). Depending 

on the atmospheric condition, either a shipyard 

competent person or a NFPA-certified Marine 

Chemist is required to test sewage tanks prior 

to entry for cleaning (29 CFR 1915.7; 1915.13). 

Sewage tanks and all piping must be tested 

and visually inspected prior to doing any hot 

work (29 CFR 1915.14) to confirm that:

• Oxygen levels in the tank and around the

work area are maintained between 19.5

and 22.0% by volume;

• Combustible gases are maintained below

10% Lower Explosive Limit (LEL); and

• Hydrogen sulfide gas is maintained at 10

ppm (parts per million) or less.

Test for oxygen, 

combustible gases 

and hydrogen sulfide 

prior to opening tank 

and entering.

Note: For more information, see CPL 02-01-051, 29 CFR Part 

1915, Subpart B, Confined and Enclosed Spaces and Other 

Dangerous Atmospheres in Shipyard Employment, May 20, 2011.

Photo: OSHA

Photo: OSHA
U.S. Department of Labor t www.osha.gov t (800) 321-OSHA (6742)

Control Measures Prior to Tank Opening 

or Pipe Breaking

• Assess and review CHT or MSD systems, components and piping.

• Perform jobsite safety and health analyses and be aware of all

associated risks and hazards. Inform all workers involved of the

risks and hazards determined by the jobsite safety and health

analyses (29 CFR 1915.3(a)).

• Post warning signs and labels (29 CFR 1915.16).

• Secure all toilets, urinals, drains, pumps, and sewage

treatment systems.

• Isolate, close, secure, divert, de-energize, lockout and apply

tags-plus applications to all valves, piping and associated

equipment (29 CFR 1915.89).

Ventilation blower and ducting.

• Strategically place drip pans at pumps, joints, disconnected

piping, tank manholes, clean-outs, drops, etc.

• Follow confined space entry testing and permitting procedures.

If feasible, use sample ports to test for atmospheric

contaminants inside the tank.

• It is recommended that a NFPA-certified Marine Chemist or

shipyard competent person be present when breaching the

sewage system, tank, or piping.

• Cautiously and deliberately remove bolts and nuts off manholes

and piping, while staying alert to any immediate change of

conditions, and be prepared to take necessary action.

• Use appropriate tools and operating procedures.

• Install and use adequate exhaust ventilation devices, ducting,

lighting, and tank-cleaning equipment. Immediately following the

piping being broken or the tank opened, apply or insert ducting

to begin exhaust ventilation. Pipe all exhausts downwind,

overboard, or away from people (29 CFR 1915 Subparts B & D).

• Cover and isolate all work areas with disposable plastic sheeting

to prevent possible contamination.

• Flush tanks and piping systems; pump and drain all residual

products.

• Check for residual pressure or vacuum effects in tanks and piping.

• While remaining outside the tank, continue to test the

atmosphere inside the tank remotely for safe conditions.

• Before beginning tank cleaning operations, while wearing the

appropriate PPE, clothing and respiratory protection, cautiously

enter the tank for an internal inspection.

• Chlorinate or sanitize the tanks and piping systems when

necessary.

Tank Cleaning Procedures

• Perform initial cleaning and any additional pumping or stripping

through the opened manhole access.

• Pressure wash, pump-out and remove all loose materials.

• Manually scrape muck or scale and bag all hardened/calcified

deposits.

• Perform a second pressure wash and remove any remaining

debris before sanitizing all surfaces with bleach or sanitizer.

• Perform final rinses, squeegee, removal, wipe and dry operations.

A cleaned and sanitized sewage tank.

Sewage Disposal

• Dispose of sewage and contaminated liquids, sludge, solids, and

all tank-cleaning wastes at local or state-approved treatment

facilities.

Post-Work Cleanup 

• Remove contaminated clothing and bag for proper disposal or

decontamination.

• Shower or wash face, arms, hands and legs with soap, using a

substantial amount of water.

• Disinfect equipment (e.g., using iodine compounds, bromine,

chlorine, ozone, or their equivalent) and wash contaminated

spaces, decks and bulkheads with detergent, sanitizer, or

bleach (29 CFR 1915.152(d)).

Photo: OSHA

Photo: OSHA
• Dispose of or re-wash rubber boots, gloves, eye goggles, face

shields and respirators with a disinfectant solution (29 CFR

1915.152(e)(v)).

• Wash contaminated clothing separately.

• Do not enter other spaces while still wearing contaminated

clothing.

Confined Space Rescue

When confined space entries are performed, have a trained rescue 

team with the proper rescue equipment available at the job site, 

or notify your designated outside rescue team in advance that 

employees are working in a CHT or MSD so they can prepare to 

respond in the event of an emergency (1915.12(e)).

Regulations / References / Literature

• OSHA’s Permissible Exposure Limits (PELs), 29 CFR 1915.1000

and 29 CFR 1915 Subpart B, D

• State Plans – www.osha.gov/dcsp/osp

• www.osha.gov/SLTC/etools/shipyard

• ACGIH’s Threshold Limit Values (TLVs)

• NIOSH/CDC’s Recommended Exposure Limits (RELs)

• www.epa.gov (Environmental Protection Agency)

• NAVSEA Standard Items 009-88; Navy NSTM 593

“Pollution Control”

• USCG, 33 CFR Part 159 MSD (Marine Sanitation Devices)

• Marine Chemist Association

• www.nfpa.org

• www.aiha.org (American Industrial Hygiene Association)

Workers’ Rights

Workers have the right to:

• Working conditions that do not pose a risk of serious harm.

• Receive information and training (in a language and vocabulary

the worker understands) about workplace hazards, methods

to prevent them, and the OSHA standards that apply to their

workplace.

• Review records of work-related injuries and illnesses.

• File a complaint asking OSHA to inspect their workplace if they

believe there is a serious hazard or that their employer is not

following OSHA’s rules. OSHA will keep all identities confidential.

• Exercise their rights under the law without retaliation, including

reporting an injury or raising health and safety concerns with

their employer or OSHA. If a worker has been retaliated against

for using their rights, they must file a complaint with OSHA as

soon as possible, but no later than 30 days.

For additional information, see OSHA’s Workers page.

How to Contact OSHA

For questions or to get information or advice, to report an 

emergency, fatality, inpatient hospitalization, amputation, or loss 

of an eye, or to file a confidential complaint, contact your nearest 

OSHA office, visit www.osha.gov or call OSHA at 1-800-321-

OSHA (6742), TTY 1-877-889-5627.

This is one in a series of informational fact sheets highlighting OSHA programs, policies or standards. It does not impose any 

new compliance requirements. For a comprehensive list of compliance requirements of OSHA standards or regulations, refer 

to Title 29 of the Code of Federal Regulations. This information will be made available to sensory-impaired individuals upon 

request. The voice phone is (202) 693-1999; teletypewriter (TTY) number: 1-877-889-5627.

DSG FS-3587 03/2013

U.S. Department of Labor t www.osha.gov t (800) 321-OSHA (6742)