9.4 Qualitative Exposure Profiling and the AIHA Risk Matrix

Qualitative Exposure Profiling and the AIHA Risk Matrix

Once the workplace is characterised and grouped, each similar exposure group must be given an exposure judgement. Most of those judgements are made qualitatively, before any pump is deployed, and the AIHA risk matrix is what converts them into a prioritised action list.

1. Step 3: Qualitative Hazard and Exposure Profiling

When quantitative sampling data are not yet available, the IH conducts a semi-quantitative risk ranking by assigning a Hazard Rating (HR) and an Exposure Rating (ER) to each SEG.

4.1 Hazard Rating (HR 1 to 4) Scale

The Hazard Rating reflects the intrinsic toxicological potency of the chemical agent, based on published Occupational Exposure Limits (OELs, TLVs, PELs), toxicological endpoints, and GHS classifications:

4.2 Exposure Rating (ER 1 to 4) Scale

The Exposure Rating estimates the magnitude, frequency, and duration of worker contact with the airborne agent, integrating volatility, handling mass, and engineering control efficiency:

$\text{Exposure Potential} \propto \frac{\text{Volatility / Dustiness} \times \text{Quantity Handled} \times \text{Duration}}{\text{Confinement} \times \text{Ventilation Efficiency}}$

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2. The AIHA Exposure Risk Matrix & Prioritization

By cross-tabulating the Hazard Rating (HR) and Exposure Rating (ER), the IH calculates the Risk Priority Rank:

$\mathbf{\text{Risk Priority Rank} = \text{Hazard Rating (HR)} \times \text{Exposure Rating (ER)}}$

+-------------------------------------------------------------------------+
|                         AIHA 4x4 EXPOSURE RISK MATRIX                   |
+-------------------------------------------------------------------------+
|  Hazard Rating                                                          |
|  (Toxicity)                                                             |
|      ^                                                                  |
|      |                                                                  |
|   4  |   Cat 2 (4)        Cat 3 (8)        Cat 4 (12)       Cat 4 (16)  |
|      |   [Medium]         [High]           [CRITICAL]       [CRITICAL]  |
|      |                                                                  |
|   3  |   Cat 2 (3)        Cat 3 (6)        Cat 3 (9)        Cat 4 (12)  |
|      |   [Medium]         [High]           [High]           [CRITICAL]  |
|      |                                                                  |
|   2  |   Cat 1 (2)        Cat 2 (4)        Cat 3 (6)        Cat 3 (8)   |
|      |   [Low]            [Medium]         [High]           [High]      |
|      |                                                                  |
|   1  |   Cat 1 (1)        Cat 1 (2)        Cat 2 (3)        Cat 2 (4)   |
|      |   [Low]            [Low]            [Medium]         [Medium]    |
|      +------------------------------------------------------------->    |
|          ER 1             ER 2             ER 3             ER 4        |
|         (<10% OEL)     (10-50% OEL)     (50-100% OEL)    (>100% OEL)    |
|                                                                         |
|                              Exposure Rating                            |
+-------------------------------------------------------------------------+

Prioritization Categories and Action Protocols

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3. SEG Management of Change (MOC) and Reassessment Triggers

Qualitative and quantitative exposure assessments represent a point-in-time snapshot. An industrial hygiene program must be linked to the facility's Management of Change (MOC) protocol to trigger exposure reassessments.

+-------------------------------------------------------------------------+
|                    MANAGEMENT OF CHANGE (MOC) TRIGGERS                  |
+-------------------------------------------------------------------------+
|                                                                         |
|  RAW MATERIAL SUBSTITUTION   ---> Solvent changes, purity adjustments   |
|  PROCESS EQUIPMENT MODS      ---> Higher throughput, increased pressure |
|  OPERATING TEMPERATURE       ---> Heating a previously ambient bath     |
|  VENTILATION ALTERATIONS     ---> LEV duct additions, fan degradation  |
|  WORK PRACTICE CHANGES       ---> Manual pouring vs automated pumping   |
|  REGULATORY / OEL REDUCTIONS ---> ACGIH TLV lowered, OSHA PEL updated   |
+-------------------------------------------------------------------------+

Periodic Audit Cadence

In the absence of an MOC trigger, SEGs are reassessed based on their assigned risk tier:

• Category 4 SEGs: Audited monthly to quarterly until engineering controls reduce risk to Category 2 or 1.
• Category 3 SEGs: Audited annually.
• Category 2 SEGs: Audited every 2 years.
• Category 1 SEGs: Audited every 3 years.

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4. Worked Step-by-Step Qualitative Profiling Examples

Worked Example 8.2.1: Multi-SEG Qualitative Risk Ranking and Prioritization in a Chemical Formulation Facility

Problem: An industrial hygienist conducts an exposure assessment in a paint and coatings manufacturing plant. The walk-through survey identifies three distinct SEGs:

• SEG 1 (Pigment Weighing & Charging): Operators manually dump 25 kg bags of crystalline silica flour (quartz, OEL = 0.025 mg/m³) into open hopper openings. Process is unventilated, generating visible dust clouds for 4 hours per shift. Handling: open manual.
• SEG 2 (Solvent Blending Tank Cleaning): Maintenance technicians clean vessel interiors using toluene (OEL = 20 ppm). Tank has dedicated local exhaust extraction (Q = 1500 cfm), but cleaning requires open solvent wiping for 45 minutes once per week.
• SEG 3 (Automated Canning & Packaging): Operators oversee an automated, fully enclosed packaging line filling cans with water-based latex resin (OEL = 10 mg/m³). No manual chemical handling; line operates with local canopy hood exhaust.

For each SEG:

1. Assign the Hazard Rating (HR 1–4) and Exposure Rating (ER 1–4) with detailed toxicological and operational justification.
2. Compute the Risk Priority Rank (HR × ER).
3. Assign the AIHA Risk Priority Category (1 to 4) and establish the immediate action protocol.

Solution Steps:

1. Evaluate SEG 1 (Pigment Weighing & Charging - Crystalline Silica):

   • Hazard Rating: Crystalline silica is an IARC Group 1 and ACGIH A2 confirmed human carcinogen (pulmonary silicosis, lung cancer) with an ACGIH TLV of 0.025 mg/m³ (< 0.1 mg/m³). → HR = 4.
   • Exposure Rating: Solid fine dust, open manual dumping, unventilated, visible dust, duration 4 hours/shift (> 50% of shift), estimated exposure > 100% of OEL. → ER = 4.
   • Risk Priority Rank: Rank = 4 × 4 = 16.
   • Risk Category: Category 4 (Critical / Unacceptable Risk).
   • Action Protocol: Immediate stop-work or mandatory supplied-air/P100 respiratory protection; install local exhaust bag-dump hoppers; immediate baseline sampling.

2. Evaluate SEG 2 (Solvent Blending Tank Cleaning - Toluene):

   • Hazard Rating: Toluene has an ACGIH TLV-TWA of 20 ppm (10--100 ppm range), produces moderate CNS depression and reproductive concerns. → HR = 2.
   • Exposure Rating: Volatile solvent (P° = 22 mmHg at 20°C), semi-enclosed tank, active LEV present, short duration (45 min/week), estimated exposure between 10% and 50% of OEL. → ER = 2.
   • Risk Priority Rank: Rank = 2 × 2 = 4.
   • Risk Category: Category 2 (Moderate / Medium Risk).
   • Action Protocol: Routine baseline monitoring (n=3--6 samples); verify LEV airflow and chemical-resistant glove selection; 2-year audit cycle.

3. Evaluate SEG 3 (Automated Canning - Latex Resin):

   • Hazard Rating: Latex resin particulate/mist has an OEL of 10 mg/m³ (nuisance particulate, low systemic toxicity). → HR = 1.
   • Exposure Rating: Fully automated, enclosed canning equipment, dedicated canopy LEV, no direct manual handling, estimated exposure < 10% of OEL. → ER = 1.
   • Risk Priority Rank: Rank = 1 × 1 = 1.
   • Risk Category: Category 1 (Low / De Minimis Risk).
   • Action Protocol: Exposures are acceptable. No quantitative air sampling required; maintain existing preventative maintenance on exhaust; 3-year audit cycle.

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Worked Example 8.2.2: Management of Change (MOC) Exposure Rating Recalculation Following Solvent Substitution

Problem: A metal degreasing operation previously cleaned precision parts in an open ultrasonic tank using 1,1,1-trichloroethane (TCA; OEL = 100 ppm, P° = 100 mmHg at 20°C), which was rated as HR=2, ER=3 (Rank=6, Category 3).

Under an MOC initiative, engineering substitutes TCA with trichloroethylene (TCE), a solvent with OEL = 10 ppm, IARC Group 1 carcinogenicity (P° = 58 mmHg at 20°C). Concurrently, engineering adds a heated vapor degreasing cycle operating at 87°C (where TCE vapor pressure reaches 760 mmHg), but leaves the open tank lip exhaust unchanged (Q = 600 cfm, imperfect capture).

1. Re-evaluate the new Hazard Rating (HR) and Exposure Rating (ER) for the TCE degreasing SEG.
2. Calculate the revised Risk Priority Rank and determine the new AIHA Risk Category.
3. Detail the required IH intervention.

Solution Steps:

1. Determine Revised Hazard Rating (HR):

   • TCE is an IARC Group 1 human carcinogen (renal cell carcinoma, non-Hodgkin lymphoma) and an ACGIH A2 suspected human carcinogen with a TLV-TWA of 10 ppm. Under AIHA hazard profiling, confirmed human carcinogens receive the maximum rating.
   • Revised Hazard Rating: HR = 4.

2. Determine Revised Exposure Rating (ER):

   • Although ambient P° is 58 mmHg, the process operates at 87°C (boiling point), causing P° to reach 760 mmHg (100% saturation above bath).
   • The tank is open, and the existing lip exhaust has not been upgraded to handle boiling vapor thermal buoyancy. Exposure potential is high to extreme (> 100% of the lowered 10 ppm OEL).
   • Revised Exposure Rating: ER = 4.

3. Calculate Revised Risk Priority Rank & Action:

   • Revised Rank = HR × ER = 4 × 4 = 16.
   • Revised Category: Category 4 (Critical / Unacceptable Risk) (escalated from Category 3).
   • Action: The MOC substitution created an unacceptable cancer risk. The IH must mandate an immediate halt to open heated TCE degreasing, require an enclosed vacuum-degreasing system or complete vapor trap chillers, mandate supplied-air respirators during any interim operation, and execute urgent quantitative personal monitoring.