Health & Safety

Exposure Assessment: Hydrochloric Acid


Union staff requested an exposure assessment during routine chemical cleaning of lavatory drain lines using Calci-Solv (active ingredient: hydrochloric, or [syn.] muriatic acid). Exposure monitoring revealed variable concentrations of HCl exposure for seven different locations in the facility, however most were above the "ceiling" limit established by OSHA. In some instances, the airborne acid concentration approached the IDLH level for short periods.

Method: Dr�ger 1/a and 50/a short-term indicating tubes

testing 1





First you pour in the acid, then you measure the airborn acidity levels with colorimetric indicating tubes.

Occupational Exposure Limits and Hygienic Values (1999): Hydrochloric Acid (syn. Muriatic Acid):


OSHA PEL (Ceiling*): 5 ppm


NIOSH REL (Ceiling): 5 ppm

IDLH: 50 ppm


ACGIH TLV "Ceiling": 5 ppm

Odor Threshold: for practical purposes, about the same magnitude as the PEL/TLV

IARC Group III (not classified as carcinogenic in humans)

*Note: The "ceiling" exposure is generally defined as the concentration that should not be exceeded during any part of the working exposure.

Test Data:

 TEST 1 - 3-17-99 1000 Men's room Union Basement WB11 - 
    2 Urinals, no fan. Vent over urinals.  16 oz Calci-solve 
    per trap.  Trap vacuumed out before treatment.  12 ppm
    TEST 2 - 3-17-99 1030 Men's room Union Basement WB11 - 
    Remaining 3 Urinals, with auxiliary (EHSRM fan at low rpm) 
    fan on.  Vent over urinals. 16 oz Calci-solve per trap.  
    Trap vacuumed out before treatment.  16-20
    ppm.  Flushes turned off for about 1 hour after treatment. 

    TEST 3 - 3-17-99  1345 Men's room Union W209 - 4 Urinals, 
    no fan.  8 oz Calci-solve per trap.  Trap not vacuumed out 
    before treatment.  4 ppm. Flushes only shut off for 5-10 
    minutes after treatment.  Some fuming still seen.  
    TEST 4 - same as TEST 3, 10 minutes later.  0 ppm. 

    TEST 5 - 3-17-99 1215 Men's room Union Basement WB11 - 
    (1.45 hours after last treatment) 0 ppm. 

    [TEST 6 - 3-17-99 1400 QC test of 0 ppm tubes using 
    concentrated product - definitely a positive response. 
    The entire tube discolors almost instantly.]

    TEST 7 - 3-17-99 1430 (est.) Men's room Union W125 - 
    no fan. 8 oz Calci-solve per trap.  Trap not vacuumed out 
    before treatment.  Very foamy.  After 5 urinals - 10 ppm.  
    [50 ppm at a sampling point very close to source.] W125 
    continued on other side. 2 Urinals.  8 oz. Calci-solve per 
    trap.  Trap not vacuumed out before treatment.  No monitoring. 

    TEST 8 - 3-17-99 1445 (est.) Men's room Union E261 - no fan. 
    8 oz Calci-solve per trap.  Trap not vacuumed out before 
    treatment.  1/8"  Debris and sludge.  2 urinals - 0 ppm, 
    5-10 minutes after pouring product. 

Observations / Questions / Comments:

  • HCl concentrations were highest immediately following the pouring of the liquid down the drain. Some drains produced larger vapor clouds than others (usually the dirtier drains). Airborne concentrations subsided to normal levels in less than 15 minutes.
  • Concentrations were highest near the floor, however acid vapor was also detected at normal breathing zone height.
  • Lavatories should be checked for proper exhaust ventilation rates.
  • Is this chemical process really necessary? Wouldn't a mechanical process work just as well for routine drain maintenance?
  • Unresolved issues:
    • Amount of product to use (e.g., 8 oz or 16 oz) for minimal exposure?

    • Should the traps be dry or wet for minimal exposure?
    • To flush, or not to flush, after adding the product?
    • Is there a reason for the variability in exposure for the various locations?


  • Using a local fan makes exposures worse.
  • Vacuuming the trap out makes exposures worse.
  • Using less product appears to reduce exposures; however, if this results in more frequent application the benefits may be minimal.
  • Dirtier traps, indicated by more foaming, result in higher exposures.
  • The exposure is worst very soon after pouring the product, exposure levels drop quickly.
  • Flushing the traps soon after using the product reduces the exposure levels down significantly.


  • There is some likelihood of chemical spills during the transfer process. According to the MSDS for hydrochloric acid, the recommended personal protective equipment includes:

    • Chemical goggles or face shield.

    • Chemical resistant gloves.
    • Clothing, to avoid skin contact.
    • Respiratory protection based on airborne levels of acid vapor. See the Respiratory Protection Index Page for additional information and requirements.
    • All staff performing this function must be informed of the associated hazards, exposure control techniques, and must demonstrate proficiency with any personal protective equipment used.


Updated November 16, 2007